MXPA06005217A - Process for colouring ceramic materials - Google Patents

Abstract

The invention relates to a new process for colouring ceramic materials by using aqueous solutions of chromophore ions. In particular, certain types of silica are added to the ceramic mixes which are to be coloured, after which aqueous or organic solutions comprising inorganic salts of Fe (Il) and/or Fe (III), or organic derivatives of Fe (II) and/or Fe (lll) are applied to the surface of the said additive--containing ceramic mixes.

Description

PROCESS TO COLOR CER MICA MATERIALS FIELD OF THE INVENTION The invention relates to a new process for coloring ceramic materials using aqueous solutions of chromophore ions.

BACKGROUND OF THE INVENTION Aqueous or hydroalcoholic solutions based on organic salts and / or chromophore ion complexes have been used for some time to decorate uncooked or partially cooked ceramic materials. Due to its diffusing properties, the coloring solutions penetrate inside the ceramic material from the surface to which they are applied, to develop "in si tu" coloration during the firing of the material. The vertical and lateral diffusion of the color solutions make it possible to obtain aesthetic effects that are highly appreciated by the market, such as smoked tone decorations, chiaroscuro effects and depth effects normally not obtainable using more traditional solid ceramic pigments. By penetrating a few milliliters into the material, these coloring solutions also make it possible to obtain decorated articles which can be maged even after cooking, by means of the Ref .: 172458 removal of its surface layer to form polished or smoothed products, without compromising the appearance of the decoration. The first coloring solutions that find industrial application in the ceramics sector were aqueous solutions of the inorganic salts of some transition metals (as described in German Patent DE 20 12 304); Subsequently, the same chromophore ions were also used in the form of organic salts and / or complexes. By using the available coloring solutions, a clearly broad color range can be obtained. For some time, the person skilled in the art has known that aqueous solutions of organic derivatives of cobalt, chromium and nickel can be used to obtain blue, green or beige colors respectively on the finished product. The search for new colors, which extend the range of colors available through the application of aqueous solutions, is nevertheless constantly on the way. The first direction of the investigation refers to the possibility of using chromophore metals different from those traditionally used to color ceramic materials: for example, European Patent EP-704-411 describes the use of aqueous solutions of organic salts of ruthenium (Ru ) to obtain the black color; German Patent DE 195 19 168 describes the use of aqueous solutions of palladium (Pd) to obtain a gray color and finally European Patent EP-1,105,358 describes the use of solutions of organic derivatives of gold (Au) to obtain colors of pink Violet. In more recent times, the research for new colorations has been directed towards the study of the combined use of color solutions containing chromophore ions and solid additives to be added to ceramic mixtures. By adding particular additives to the raw materials, new and unpredictable colorations can be obtained, since the additive interacts with the chromophore ions to modify the chromatic performance. Thus, for example, European Patent Application EP-888,260 describes a process for obtaining certain new colorations based on the addition of Ti02, Sn02, Zr02 and ZrSi04 to the ceramic mixture, followed by treatment with aqueous dye solutions of chromophore ions. . As a further example, document WO02 / 10092 describes the coloring processes that require the addition of low melting point additives such as zinc oxide or zinc silicate to the ceramic mass, to obtain pink-orange shades on the surface of the ceramic material. Despite the research carried out so far, no coloring process is currently known which uses aqueous dye solutions, that makes possible the development of color tones in the range of coffee-red to pink-orange, in particular of the red-brown tones, which are going to be obtained on the surface and / or inside of the ceramics material . To obtain these colorations it is known from the state of the art to use solid ceramic pigments based on iron, either natural (Gres de Thiviers) or synthesized (Gres de Thiviers sintético). Solid pigments are normally added throughout the entire ceramic mix, so that a brown-red color develops throughout the entire thickness of the article; With this technique only simple decorations with limited aesthetic effects (salt and pepper type) can be obtained. Alternatively, the solid pigments can be applied superficially on the stoneware by silk mesh printing; in this way, decorations similar to those achieved using aqueous dye solutions of soluble compounds can be obtained, but only on the surface of the tiles, without however obtaining the high aesthetic results required by the market and made possible only by the aqueous dye solutions (Smoke effect, chiaroscuro effects and depth penetration). Natural Stoneware of Thiviers contains approximately 90% silicon oxide in the form of quartz and 10% goethite (FeOOH). Various methods for preparing synthetic Thresorware are known in the prior art; of the European Patent Application EP-933,404 it is known for example to prepare a dye which consists of synthetic Thiviers stoneware starting from iron compounds, a powdery matrix which consists of an oxide and / or a silicate (in particular amorphous silicate) and one or more auxiliary substances. According to this process, the iron compound is placed in intimate contact with at least 50% amorphous powder matrix, which has a surface area exceeding 40 m2 / g, possibly in the presence of silicon oil-type auxiliary substances, a variable time between 0.1 and 10 hours. These dyes can be used in a similar way to traditional pigments for the complete coloring of ceramic materials. Alternatively, these can be used as components for the preparation of coloring compositions for surface applications. Even if they are applied to the surface of ceramic material in the form of coloring compositions, the presence of suspended oxides and / or silicates in the composition prevents penetration of the color into the interior of the ceramic mass. Therefore, it is not possible, even using these dyes as dyes applied to the surface of the material, to obtain a red-brown coloration inside the ceramic mass that allows aesthetic results comparable to those obtainable with aqueous ionic solutions. chromophores.Technical problem The technical problem therefore exists in finding a new process for coloring ceramic materials on the surface and / or in the interior, using color solutions containing chromophore ions, which makes possible, after cooking: a) the achievement of colors currently not yet obtainable with this coloring method, b) improved access to colors currently available, but exclusively through the process which has the disadvantage of regulating a strong rebalance of the ceramic mixture, to avoid the fusion capacity excessive caused by low melting point additives.

BRIEF DESCRIPTION OF THE FIGURES Figure 1 is a photograph of a ceramic tile prepared and treated with the method according to the present invention, in particular of Example 3 [for example using 5% wide pore silica gel (Wide Pore silica Meigao Chemicals as an additive to the powder for porcelain stoneware ARKIM, based on the present Application and 2.5% aqueous iron (as ammonium citrate) as staining solution (1 drop; weight 0.047 ± 0.005g, average diameter of color spot formed: 1.3 cm), the tile has been smoothed after development] taken at the limit line of the applied drop of the coloring solution and showing that the ceramic articles obtainable according to the method of the present invention show chromophore microparticles of approximately 1-60 μm, preferably from 5 to 60 μm in diameter, resolvable with an optical microscope of up to 200 amplifications (preferably up to 400 amplifications) operated with external polychromatic light provided through an optical fiber equipped with a "daylight" filter. Figure 2 is a photograph of a ceramic tile prepared on a metallic net and treated with the method according to WO02 / 10092, in particular a tile obtained employing 12,5% ZnO as additive to the powder porcelain stoneware ARKIM referred in the present Application, and 4.4% aqueous chromium (as acetate) as a dye solution (1 drop, weight 0.047 ± 0.005 g, average diameter of the color point formed: 1.3 cm); the tile, due to its lack of uniformity that has not been smoothed after development, taken on the boundary line of the drop applied to the dye solution with an optical microscope to 200 magnifications (preferably up to 400 magnifications) operated with polychromatic external light provided through an optical fiber equipped with a "daylight" filter. Figure 3 is a graphical representation of the values of delta a * and the delta L * values of the coloration tests (smoothed) reported in Table 6 of WO02 / 10092, and of Examples 1-5, 12-47 reported in the present Patent Application. Figure 4 is a graphical representation of the values a * and b * of the staining tests (smoothing) reported in Table 2 of WO02 / 10092, and of Examples 1-5, 12-25 reported in the present Patent Application .

DETAILED DESCRIPTION OF THE INVENTION The above and additional technical problems will appear in the present and then are solved by a new coloring process which makes possible a variation of the resulting color of the iron-based coloring solutions to be obtained on the surface and / or the internal part of the baked ceramic material, characterized by: (a) the addition of the ceramic mixture from 1% to 15% by weight, with respect to the dry ceramic mixture, the precipitated silica and / or silica gel it has an active surface S = IOO m2 / g at the moment of coloring, and the active surface S that is defined by the formula S = A * Gr, where: Gr is the fraction of the particle size -expressed in volumetric percentage- included between 5 and 60 micrometers for the precipitated silica and between 1 and 60 micrometers for silica gel, and A is the surface area of the silica, expressed in m2 / g as measured by the BET method; (b) applying to the surface of the ceramic mixing solutions containing additive comprising iron, in particular aqueous or organic solutions comprising inorganic salts of Fe (II) and / or Fe (III), or organic derivatives of Fe ( II) and / or Fe (III); (c) the resulting color variation that is equal to? E > 6. In the CIELab system the quantity? E expresses the difference between two colors and is defined based on the difference between the coordinates L *, a * and b * of the color of interest (sample) in comparison with the chromatic coordinates of the standard ( std), by the formula? E = [(? L *) 2 + (? a *) 2 + (? b *) 2] 1/2 in which? L * = L * (sample) -L * ( std),? a * = a * (sample) -a * (std) and? b * = b * (sample) -b * (std) The process of the invention makes possible a variation in the color resulting from the solutions Iron-based dyes that are to be obtained, equal to? E > 6, assuming as reference (std) the coloration developed by the same solutions of the same ceramic mixture without the addition of silica. Although normally two colors are visually perceived as different if? E > 1, a difference? E > 6, characterized by a positive delta a * (increase in the degree of red) and a negative contribution delta L * (increase in color intensity), it is in this case necessary to obtain a reddish-brown tone of commercial interest. The variation described above in the chromatic performance is due to the interaction between the iron chromophore ion and the silica, according to the invention, added to the ceramic mixture. On the ceramic material obtained from the mixtures of traditional composition, the color solutions based on iron develop, after firing, a coloration of beige to brown black on the non-smoothed material and various shades from beige to light brown in The interior of the ceramic body, depending on the depth of smoothing or softness, the amount of iron applied which in turn is a function of the amount of solution used, and its iron concentration. The addition of silica according to the process of the present invention to the mixture makes it possible to obtain the coloration of the coffee-red to the pink-orange, in particular of the red-coffee, on the surface, on the non-smoothed ceramic material, and inside the ceramic mass, and therefore on a smoothed product. The present invention also relates to the ceramic mixture containing the precipitated additives or silica gel according to the present invention, as well as the final ceramic article obtainable through the process described herein. Within the color space L * a * b *, L * indicates the brightness and is a value that varies between 0 and 100 (in which 0 represents black and 100 white); a * and b * represent respectively the red (+ a *) / green (-a *) component and the yellow (+ b *) / blue (-b *) component. In terms of difference in the chromatic coordinates, the process according to the invention makes it possible to obtain an? E > 6 which is essentially manifested by:? L * negative, for example, the color obtained on mixtures with silica added according to the invention is "darker" than the reference color, and the? A * positive, for example the The resulting color of the iron solutions on ceramic mixtures with added silica according to the invention has a greater red component. The precipitated silica and the silica gel usable for implementing the invention are characterized by an active surface S = IOO m2 / g defined by the formula S = A * Gr, where S represents that portion of the total surface area (A) that is derived of the percentage fraction of the silica that has the "active particle size" (Gr). As is customary in this technical field, the percentage values of Gr are expressed as volume percentage (% V / V). Example: a silica gel having A = 250 m2 / g and Gr of 50% will have S = 125 m2 / g. The active particle size is between 5 and 60 micrometers for the precipitated silica and between i and 60 micrometers (preferably between 2 and 60 micrometers) for the silica gel. The fraction of the active particle size identifies the silica, which at the time of the treatment of the mixture containing the additive with the coloring solutions, possesses the adequate particle size to interact with said solutions, giving rise to the variation in the resulting color. The variation in the resulting color is uniform for silicas that have active particle size Gr within the indicated range; Precipitated silica and silica gel with a particle size exceeding 60 micrometers give rise to unequal (dotted) color variations, with unsatisfactory aesthetic results. Precipitated silicas with a particle size of less than 5 micrometers and silica gel with a particle size of less than 1 micrometer do not give rise to significant chromatic variations. The particle size referred to is that obtained by a particle size analyzer with laser diffraction detector as established in ISO 13320 (1999), equipped with the wet sampler. The silica samples are usually treated before analysis (for example by stirring, ultrasonic treatment or addition of surfactants) to obtain a stable dispersion of the particles in the solvent used for the determination (in general water). In the case of precipitated silicas and silica gels these treatments break labile tertiary structures (aggregates) and the measured particle size corresponds to that of secondary stable particles (agglomerates). A represents the total surface area of the silica expressed in m2 / g and measured using the B.E.T method. (nitrogen porosimeter). For porous materials, the contribution by the external surface of the particles to the surface area is negligible, and the total surface area coincides almost completely with the internal surface area which is derived from the porosity of the material. Therefore, the greater the total surface area; greater is the porosity of the material. In order to satisfy the condition S = IOO m2 / g, the precipitated silicas and the silica gels usable for implementing the invention must be porous materials, for example these must have a B.E.T. of A = IOO m2 / g which is derived from the internal surface of the pores and at the same time must have adequate particle size, ie a fraction of particle size Gr between nearest to 100% the closest value of the surface area When it exceeds 100 m2 / g. Silicas that have a low surface area due essentially to the outer surface of the particles have S-values less than 100 m2 / g and are suitable for use in the process of the invention. In this respect, they do not possess sufficient porosity and therefore sufficient active surface S, whatever their fraction of active particle size Gr. Even silicas with surface area A > 100 m2 / g, which are essentially derived from the external surface area of the particles, can not be used in the process of the invention. These would have in this respect an extremely fine particle size and a fraction Gr of active, low or zero particle size, and could therefore have an active surface S less than 100 m2 / g. The process of the invention can be implemented by adding the precipitated silica and / or silica gel to the raw materials or to the piece. The first possible mode of the process involves mixing the precipitated silica and / or silica gel with the raw materials upstream of the total production cycle. In this case, as the silicas are subjected to a grinding process together with the raw materials with which they are mixed, the initial particle size of the silicas can be totally or partially greater than 60 microns and the active surface S can initially be less than 100 m2 / g. The grinding does not significantly include the surface area of the silicas, although its particle size distribution strongly influences: during grinding, the particle size is reduced and the Gr fraction of the active particle size is increased. In this way, the value of the active surface S becomes > 100 m2 / g at the time of treating the material containing the additive with the coloring solutions. A second embodiment of the process of the invention involves mixing the precipitated silica and / or silica gel with the piece leaving the mills. In this case, the silicas do not undergo additional grinding processes; for this reason, the active surface S of the precipitated silica and / or the silica gel added to the piece must already be > 100 m2 / g at the moment that is added to the mixture. This means that the initial particle size of the silica must be characterized by a particle size fraction Gr already within the optimum range. To implement the process of the invention, the precipitated silica and / or the silica gel are added to the ceramic mixture in a total amount of between 1% and 15% by weight, preferably between 2% and 10% by weight, more preferably between 3% and 7% by weight of dry silica with respect to the dry ceramic mixture. The addition of an additive to a ceramic mixture should influence as little as possible any of the technical characteristics of the finished product (tile), or the technical characteristics of the mixture itself, in particular its processing capacity (given for example by the viscosity, density, etc); the addition of precipitated silica and / or silica gel in percentages exceeding 15% by weight, allows the process of the invention to be equally implemented, but has disadvantages which render the invention impossible to apply on an industrial scale. For example, the final tensile strength of the uncooked tiles decreases drastically which makes it impossible to automatically decorate the ceramic material containing the additive, and at the same time the shrinkage during cooking increases, compromising the flatness of the tiles. Preferably, the total amount of the silica added to the ceramic mixture is between 2% and 10% by weight, even more preferably between 3% and 7% by weight of the dry silica with respect to the dry ceramic mixture. The addition of silica according to the invention to a mixture of traditional composition may require a reformulation of the mixture itself by adequately modifying the composition by weight of the raw materials, or by adding additives known to the person skilled in the art, such as deflocculators. (for example tripolyphosphates, polyacrylates, silicates, etc. or their mixtures) and binders (polyacrylates), with the aim of maintaining the technical characteristics of the finished product (final tensile strength, shrinkage, flatness, resistance to staining) within values standards Excess tripolyphosphate can reduce the result, and therefore mixtures of sodium silicate / sodium polyacrylates, or other deflocculators, are preferred. In the case where the ceramic article is made of a plurality of different ceramic mixtures subject to no or only partial homogenization one among the other (according to the so-called "malmiscelati" technique which consists of loading the mold of different ceramic mixtures which are not, or are only incompletely mixed one with the other, such as to preserve the volume elements showing the same or substantially the same composition as the constituent mixtures), at least one of the individual mixtures used it should comprise the precipitated silica and / or the silica gel according to the invention in an amount between 1% and 15% by weight, preferably between 2% and 10% by weight, more preferably between 3% and 7% by weight. It is immediately apparent, that in this case, the desired color will be developed, in interaction with the external application pattern of the iron-based coloring solution, only in the surface layers of the ceramic article exposed by the homogeneous volume elements that exist within the complete ceramic body, and comprising the precipitated silica and / or the silica gel according to the invention, at least in the prescribed amounts. In order to carry out the coloring process of the invention, the ceramic materials to which the precipitated silica and / or silica gel have been added are treated with solutions comprising iron, in particular with aqueous solutions or organic inorganic salts of Fe (II) and / or Fe (III), or organic derivatives of Fe (II) and / or Fe (III). Aqueous dye solutions containing from 0.1% to 20% by weight of iron (expressed as elemental Fe) are preferred particles to implement the process of the invention. The inorganic salts (comprising inorganic complex salts) of Fe (II) which can be used to implement the invention are inorganic salts soluble in water or which can be made soluble in water by reaction with mineral acids. Particularly preferred are aqueous dye solutions containing iron (II) ammonium sulfate, iron (II) sulfate, iron (II) chloride, iron (II) perchlorate, potassium hexacyanoferrate (II), hexacyanoferrate (II) of ammonium. Among the inorganic salts of Fe (III) (which comprise complex inorganic salts of Fe (II)) usable to implement the invention, which are likewise soluble in water or which can be made soluble, there is potassium hexacyanoferrate (III) . The organic derivatives of Fe (II) and / or Fe (III) are preferably salts and / or complexes of Fe (II) and / or Fe (III) with organic compounds selected from the group: acetylacetone; ascorbic acid; carboxylic acids of the general formula Ri-COOH and / or a sodium, potassium or ammonium salt thereof, in which R x represents hydrogen, a benzene ring or an alkenyl or alkenyl group of 1 to 9 carbon atoms, possibly substituted with 1 to 6 groups -COOH, -OH-, -NH2 and / or -SH; Amino acids of the general formula and / or the sodium, potassium or ammonium salts thereof, where R2 = -H, -CH3, in which X = -H, -CH3 and Y = -H, -OH where R3 and R may be the same or different from each other and represent hydrogen, an alkyl group of 1 to 4 carbon atoms possibly substituted with -OH, - (CH2) n -COOH groups where n = l-3, - (CH2) m-NH (2_i) - (CHR5-COOH)) k where m = l-6 and k = l or 2, and where R5 = -H, -CH3, which X = -H, -CH3 and Y = -H, -OH.

Said salts and / or organic complexes are commercially available or can be easily prepared by the person skilled in the art by the reaction of an inorganic iron salt and the corresponding acid or carboxylate; its solubility in water can be increased by partially qualifying acid functional groups with ammonia, KOH or NaOH or functional groups with acids. The aqueous solutions of the organic derivatives of Fe (II) and / or Fe (III) obtained in this way can be used as such, as coloring solutions. Non-limiting examples of the colorant solutions which can be used to implement the invention are aqueous solutions of salts and / or organic complexes of Fe (II) and / or Fe (III) with acetic propionic, butyric, lactic, glycolic, osical acids, tartaric, citric, maleic, fumaric, citraconic, gluconic, aminoadipic, aminobutyric, aminocapronic, aminocaprylic, 2-amino-4-hydroxybutyric, aminoisobutyric, levulinic, thioglycolic, salicylic, glycine, ethylenediaminetetraacetic acid (EDTA), acid 1,3- propylenediaminetetraacetic acid, ethylenediamine-N, N'-bis (2-hydroxyphenylacetic acid) (EDDHA), ethylenediamine-N, N'-bis (2-hydroxy-4-methylphenylacetic acid) (EDDHMA), diethylenetriaminepentaacetic acid (DTPA), hydroxyethylene diamine triacetic acid (HEDTA), nitriloacetic acid. In a particularly preferred embodiment of the process according to the invention, an aqueous solution of iron-ammonium citrate containing from 0.3 to 20% by weight of iron (expressed as elemental iron) is used to color the ceramic material which contains the additive. Even more preferably, an aqueous solution of iron-ammonium citrate containing from 1 to 20% by weight of iron (expressed as elemental iron) is used. The aqueous dye solutions used to carry out the process according to the invention can also comprise, to modify the physical characteristics such as density, wetting powder, pH, adsorbance by supports, viscosity and others, one or more appropriate modifiers of the characteristics previously mentioned, such as acids or bases, surfactants, etc. and also, importantly, one or more water-miscible solvents such as: water-soluble alcohols, propylene glycols, ethylene glycols, glycol ethers, etc. The feature of the invention, for example an increase in delta a * and a reduction in delta L *, taking into account that red is one of the fundamental colors, is also extremely useful for obtaining interesting chromatic variations of the colors currently available. Accordingly, dye solutions containing iron, in particular aqueous or organic solutions comprising iron in the form of inorganic salts of Fe (II) and / or Fe (III), or organic derivatives of Fe (II) and / or Fe (III) usable to implement the invention, may also comprise other chromophoric metal ions, in the form of inorganic salts and / or organic derivatives of chromophoric metals, chosen from the metals of the main group as well as the transition metals and lanthanides. actinides, preferably chosen from the group: Co, Ni, Cr, Ru, Au, Mn, Ti, Zn, Zr, Sb, V, W, Pd or their mixtures. The color solutions contain 0.1 to 18.2%, preferably 0.3% to 18.2% by weight of iron (expressed as elemental iron), with a maximum cation concentration of 20%, preferably 19.5%, and an Fe / Me ratio between 15/1 and 1/5, preferably between 13.9 / 1 and 1/5. The coloring process of the ceramic materials according to the invention involves the following operative steps: (a) adding the precipitated silica and / or the silica gel according to the invention to the ceramic mixture to be molded in an amount between 1% and 15% by weight, preferably between 2% and 10% by weight, more preferably between 3% and 7% by weight of dry silica with respect to the dry ceramic mixture; (b) molding the ceramic mixture; (c) drying the molded ceramic material; (d) treating the ceramic material derived from the preceding step with at least 2 g / m2, preferably at least 10 g / m2, of coloring solution; (e) drying the ceramic material derived from the preceding step; (f) cook the ceramic material. The process of the invention is particularly suitable for coloring the ceramic material intended for smoothing or smoothing, preferably porcelain stoneware. Step (a) is achieved by the addition of silica either to the ceramic raw materials before grinding or to the resulting piece of grinding, where after this the piece obtained in this way is atomized in powder form to allow its subsequent molding. Step (b) is carried out on the spray obtained according to step (a), using pressing techniques for ceramic materials currently in use (single, double or multiple load). 0, in the case of the extruded material, step (b) is carried out by extruding a wet paste. Step (c) is usually conducted at temperatures of about 100 ° C to 120 ° C and acts to reduce the water content of ceramic material below the critical level imposed by the characteristics of the rapid firing cycle of the ceramic plants modern This critical level varies according to the ceramic material and the relative firing cycle; by way of example, the residual water content of a porcelain stoneware after drying is generally less than 0.5%. One or more intermediate steps (c ') of the pretreatment of the dried ceramic material can optionally be undertaken between step (c) and step (d), using water or aqueous solutions of mono- or poly-carboxylic acids or their salts . Preferably, the mono- or polycarboxylic acids containing from 1 to 10 carbon atoms, possibly with 1 to 5 hydroxyl, amino or thio substituents in the aliphatic chain, possibly partially or completely salified with ammonium, amines and / or alkali metals and / or alkaline earth metals. Up to 300 g / m2 of the pre-treatment solution are normally applied. Preferably, the pre-treatment is achieved by disc or spray applications. The treatment of the ceramic material as described in step (d) takes place by application techniques known to the person skilled in the art: painting, spraying, disk spraying, printing by flat or rotating silk mesh, printing with cylinders of silicone, digital printing with the drop-on-demand ink system, or magnetic deflection, in order to form designs and decorations that completely or partially cover the treated ceramic surface. According to the application technique used, the coloring solutions must be of different viscosities at the time of use; for this reason, the dye solutions are usually made thick in a paste with suitable thickeners, in general natural gums or starches, or well-known inorganic thickeners. For example, among the first inorganic thickeners, also the mixture of ceramics effectively employed, suspended in appropriate amounts to modify the viscosity of the coloring solution to the desired degree, can be employed. The treatment with dye solutions in step (d) can be achieved by means of one or more successive applications; between two successive applications, the material that is decorated could be left to dry for a variable period of time. Suitable dye solutions for digital printing can be totally or partially water-based, such as the aqueous dye solutions already described above, which can comprise water-miscible solvents, or can be based entirely on organic material, depending on the characteristics of the ink jet head: if the head can not use conductive liquid, the iron-based coloring solutions employed by the present invention have to be formulated using known iron derivatives suitable for use in non-aqueous liquids for example as iron octanoate in aromatic hydrocarbon solvent, as described for example in WO01 / 51573 incorporated by reference herein, or other organic iron derivatives in suitable organic solvents. As the aqueous dye solutions, also the organic dye solutions should contain 0.1% to 20%, preferably 0.3% to 20%, more preferably 1% to 20%, most preferably 1% to 10% by weight of iron (expressed as iron elementary) Optionally, the decorated ceramic material can be further processed by means of one or more intermediate passages (d ') between step (d) and step (e), with water or aqueous solutions of mono- or poly-acids. carboxylic acids or their salts. Preferably, the mono- or polycarboxylic acids or their salts. Preferably, the mono-polycarboxylic acids containing from 1 to 10 carbon atoms, possibly with 1 to 5 hydroxyl, amino or thio substituents in the aliphatic chain, possibly partially or completely salified with ammonium, amines and / or alkali metals and / or alkaline earth metals, in general up to a maximum amount of post-treatment solution of 300 g / m2. The post-treatment solutions may also additionally or exclusively contain inorganic salts such as sodium, potassium or ammonium chloride or fluoride. Preferably the post-treatment is achieved by disc or spray applications or by mesh applications using suitable meshes to deposit the desired amount. The objective of the drying step (e) is the uniform absorption of the coloring solution and can be achieved at temperatures between room temperature, with prolonged periods of balance (approximately 8 hours), or at temperatures of approximately 60-70 ° C, by shorter rolling periods (approximately 60 minutes). The firing cycle in step (f) depends on the type of material treated; In the case of porcelain stoneware, a standard cooking cycle lasts 45 to 65 minutes (from cold to cold) and a maximum cooking temperature of 1200 to 1220 ° C. The process of the invention makes it possible to vary the chromatic performance of the coloring solutions to be obtained, on the surface and / or interior of the decorated ceramic material, to the depth necessary to allow any subsequent machining. Based on the application technique used, the depth can be regulated by adjusting the viscosity of the solution, the amount of iron applied, which in turn is related to the amount deposited and the concentration of iron and on the numbers of pre- and post-treatments carried out. The penetration depth can reach up to 4 mm. The decorated ceramic materials can therefore be subjected, after firing, to subsequent machining by means of satinization, smoothing, polishing or burnishing, according to the desired aesthetic effect, by removing the material from the surface at a depth in general. that exceeds 50 μm. In any case, the depth of penetration is such that even up to 3 mm of material can be removed by machining, this being particularly important on tiles of large size (up to one square meter), and a possible curvature that occurs during cooking gives as a result considerable deviations in flatness at points distant from the center of the curve, thus requiring machining at a greater depth in order to restore flatness. As it is apparent from the above, on top of the new brown-red color provided only by the present invention, it is a marked advantage of the present invention that it achieves its objectives through the use of the specific types of silica described in the present, as additives for the ceramic mass, which are additives that influence as little as possible any of the technical characteristics of the finished product (tile), or the technical characteristics of the mixture itself, in particular its processing capacity ( given for example by viscosity, density, etc.). In contrast to this, the addition of conventional additives such as ZnO and zinc silicate to the ceramic mass exerted a pronounced melting action on the mixture (thus leading to the formation of extended, obligatory glass phases, on the one hand, for the development of color, but which give rise, on the other hand, to molten materials, which partially lose their shape after cooking). Such fusion action gives problems, in the case for example of tiles, since without any countermeasure taken, the planarity of the tiles resulting from the firing of the raw bodies contaminated with ZnO or with zinc silicate is considerably reduced, in particular between the larger the dimensions of the raw bodies. While the melting or melting action could be balanced, to a certain extent, through the addition of refractory materials, it is evident that the more additions will be made, the more difficult it becomes to fully restore the original performance of the ceramic mass. In practice, the addition of refractory materials not only involved additional expenses and additional specific adaptations, but it was also particularly laborious and could almost never be carried out beforehand, since the degree of the balance itself depended on the dimensions of the articles of ceramic that are finally obtained. It is therefore a merit of the present invention to have overcome the prior need to rely on the formation of glass phases within the ceramic material to develop the desired colors. It is an additional merit of the present invention to have obtained a color range substantially contiguous to that obtainable with the method of WO02 / 10092, which includes important new colors, such as red coffee. Above all, it is an advantageous feature of the present invention to have displaced the chromatic iron fingerprint to pronounced, dark, red hues, particularly adapted for mixing with additional chromophores. The diversity in the mechanism of color formation between the method of WO02 / 10092 and the present invention, becomes evident already from the respective displacements in delta L * values obtained, which are diametrically opposed: while with the present invention the positive values of delta a * and the negative values of delta L * are obtained, the method of WO02 / 10092 gives (always with positive delta values a *) values of delta L *. It is also noted that the present invention gives, generally speaking, L * values smaller than WO02 / 10092, which means that the colors of the inventions are darker than those comparatively light and clear from the prior art. Furthermore -always with respect to the difference in the mechanism of color formation- while in the present invention, the discrete microparticles of the desired color are formed within the ceramic mass, which can be resolved under defined conditions of optical observation, no formation of discrete colored particles according to WO02 / 10092 is observed, where the coloration arises, rather, from the formation of the extended colored glass phases, originated by the improvement of the fusion capacity exerted by the ZnO and / or the zinc silicate. The preferred but not exclusive embodiments of the present invention are described in the following examples. These and the additional embodiments of the present invention are encompassed by the appended claims and by any combination of said claims one among the other.

EXAMPLES All the following examples were implemented by the addition of silicas to an atomized porcelain stoneware powder, supplied by ARKIM S.p.A. Cooperativa Cerámica d 'Imola S.p.A., whose composition by weight of oxides before the addition of the additive is as follows: The powder was prepared using a fluidized piece with a mixture of sodium silicate and sodium polyacrylate. Samples and tiles were baked in an industrial oven with a 60 minute porcelain stoneware firing cycle (cold to cold) at a maximum temperature of 1200 ° C. Some samples and tiles were smoothed using diamond wheels at a depth of approximately 0.6 mm. The color measurements were carried out according to the system L * a * b *, using a colorimeter of Dr. Lange, Spectrapen Model (LZM224 -Standard No. 1009). The particle size of the silicas was measured by supplying 0.1 g of silica in distilled water containing 0.05% surfactant (sodium hexametaphosphate or sodium pyrophosphate). The samples were analyzed with a Malvern 2000 particle size analyzer after having been subjected to ultrasonic treatment at maximum power for times ranging from 1 to 30 minutes, depending on the state of initial aggregation of the sample. Surface area measurements by the B.E.T. method were obtained using a nitrogen porosimeter Micromeritis ASAP2010 used on silicas as such. All delta E values that follow refer to the difference in the resulting color between the color solutions applied to the mixture containing additive and aguellas applied to the additive-free mixture.

EXAMPLES 1-5 100 g of atomized ceramic mixture were assorted in water (water ratio: mixture = 1: 2). 5% by weight, with respect to the dry ceramic mixture, of each silica was added under agitation to the obtained piece. The ceramic mixture with the additive was dried in an oven at 100 ° C until its weight was constant, then it was crushed (zero residue on a 1 mm mesh screen), rehydrated to a water content of 5% and It was pressed into test samples of dimensions of 110 x 55 mm. The ceramic material formed was dried in an oven at 100 ° C until a residual water content of less than 0.5% was obtained. The characteristics of the silicas used: The examples were implemented by the application of a drop (weight: 0.047 + 0.005 g, average diameter of the color point formed: 1.3 cm) of the aqueous solution of iron and ammonium citrate which contained 1% iron by weight Sample test samples intended to remain in the rough state, and containing 2.5% iron by weight, on top of test samples intended to be smoothed. The dye solutions were obtained by dissolving the iron and ammonium citrate which contained 28% iron by weight in an aqueous solution of 10% by weight ammonium citrate.

Example SLOW SMOOTH No. L a * b *? E L a * b *? E 1 65.34 11.06 18.61 10.47 71.98 7.25 10.45 10.64 2 61.90 13.45 15.29 14.56 67.81 10.53 11.17 15.96 3 61.04 16.15 18.86 17.25 66.11 10.30 12.32 17.45 4 58.35 16.76 24.61 20.86 64.37 8.67 16.56 19.45 59.55 18.06 16.04 19.28 63.96 12.60 12.90 20.52 STANDARD 73.48 4.75 16.74 81.10 1.90 9.30 additive free EXAMPLES 6-11: COMPARATIVE Test samples of the mixture for the porcelain stoneware were prepared as described in Examples 1-5, adding the silicas with the following characteristics to the atomized ceramic mixture.

The examples were implemented by applying a drop (weight: 0.047 ± 0.005 g) average diameter of the color point formed: 1.3 cm) of the aqueous solution of iron citrate and ammonium as in Examples 1-5.

(*) Dotted surface whose measurement of the values L * a * b * is not indicative, the points have been caused by the excessive dimensions of the silica particles used.

EXAMPLES 12-14 Tiles of 33 x 33 cm were prepared and colored according to the following process: (a) 5% by weight of silica gel from Wide Pore Silica from Meigao Chemicals (Gn = 91.86%; A = 283.7 m2 / g, S = 260.6 m2 / g) was added to the silica of the porcelain stoneware mixture and the mixture containing the additive was atomized to obtain a powder. (b) the powder mixture with silica additive was formed into tiles 33 x 33 cm in size; (c) The tiles were dried in a dryer at a maximum temperature of 120 ° C with a drying site at approximately 60 minutes; (d) Aqueous dye solutions at various concentrations of iron in the form of iron and ammonium citrate, thickened to the correct viscosity by the addition of modified starch for use with 36- or 90-wire meshes, were applied to the ceramic material formed, using silk mesh printing; (d ') the ceramic material was post-treated with an 8% aqueous solution of 1,2,3-trihydroxycarbonyl-sodium propane at 220 g / m2; (e) The decorated ceramic material was dried at room temperature for approximately 6 hours; (f) The tiles were baked in an industrial oven with a cooking cycle of 60 minutes (from cold to cold) and at a maximum temperature of 1200 ° C. After firing the tiles were smoothed to a depth of approximately 0.6 mm. * the meshes of 36 and 90 wires deposit 64.8 and 29.6 cc / cm3, square meter respectively.

EXAMPLES 15-25 Various iron derivatives II and III. The mixture with added silica as described in Examples 1-5 was formed in tiles of dimensions 33 x 33 cm on which 2 drops were applied (average total weight: 0.0094 + 0.005 g, average diameter of the color point formed : 1.8 cm) of each coloring solution. Color solutions containing 1.0% iron by weight (expressed with Fe) were applied to the tiles intended to be rough, while solutions containing 2.5% iron were applied to the tiles intended for smoothing. It was subsequently observed how the tiles were baked in an industrial furnace and smoothed.

Characteristics of the silicas added to the mixture: Trade name: Wide Pore Silica - Meigao Chemicals: Gr = 91.86%; A = 283.7 m2 / g; S = 260 m2 / g (as in the previous example 3).

Coloring solutions used: Example? O. 15 hexacyanoferrate (II) potassium 15 bis hexacyanoferrate (III) potassium 16 iron (II) ammonium sulfate 17 • iron (II) chloride 18 iron (II) sulfate 19 iron (III) sulfate 20 iron oxalate ( III) -ammonium 21 pentetate disodium iron (III) (* Aldrich 27459-5G: disodium salt of iron (III) of diethylenetriamine pentaacetic acid, 98% dihydrate) 22 ascorbate iron (II) 23 iron-ammonium complex of Ethylenediaminetetraacetic acid 24 Iron (II) gluconate: The aqueous coloring solution was obtained during the addition of a 30% aqueous solution of ammonium hydroxide to the iron (II) gluconate until the compound dissolved. 25 iron glycinate hydrochloride: The aqueous coloring solution was prepared by reacting FeCl2 * 4H20 with glycine, EXAMPLES 26-47 On 3 x 33 cm tiles prepared as described in Examples 15-25, 2 drops (total weight = 0.110 ± 0.005 g, average diameter of the color point formed: 1.6 cm) of each coloring solution were applied which contained iron - in the form of iron-ammonium citrate - and other chromophoric metals in the form of the following salts and / or complexes: manganese and ammonium citrate, zinc and ammonium citrate, cobalt and ammonium citrate, citrate vanadium and ammonium, zirconium carbonate and ammonium, ruthenium glycolate, titanium and ammonium lactate, chromium and ammonium citrate, nitrile and ammonium citrate, gold acetylcysteinate. Where it is not expressly indicated, the smoothing was 0.6 - 0.8 mm.

Smoothing variable from 1.8 to 2.2 mm For higher quality, the colors and the L * a * b * of the tests 26-47 are given at once color of the rough support free of additive color of the rough support which contains additive color of the smooth support free of additive color of the smooth support contains additive EXAMPLES 48-53 Tests with individual cations Using the same procedure as in Examples 26-47, solutions containing the individual cations without the iron, were tested to show, comparing them with the results of the mixtures containing iron, the strong influence of the same ones on the chromatic digital fingerprint. The tiles were smoothed to a depth of 0.3 - 0.5 mm. The characteristics of the silica used in the mixture. Commercial name: Wide pore Silica - Meigao Chemicals; Gr = 91.86%; A = 283.7 m2 / g; S = 260 m2 / g.

EXAMPLES 54-58 Tests using the silk mesh application of the 90-wire mesh mixtures Using the same procedure as Examples 12-14, some solutions containing iron and other cations were tested. The compounds used to produce the cations other than iron in the solutions are listed in the description of Examples 26-47.

EXAMPLE 59 (COMPARISON) To investigate the formation of the color according to the present invention and according to WO 02/10092, the chromatic coordinates of the examples (smoothed modalities) cited in WO 02/10092 were compared to the chromatic coordinates of the examples of the present invention (smoothed modalities) cited hereinabove. In the following tables 59 (1) and (II), the respective delta L * values and the delta a * values are described: Table 59 (1): value of delta a * and delta L * according to the invention (taken from the previous respective examples). 15 20 25 Table 59 (11); delta a * and delta L * according to WO 02/10092 (taken from the respective examples of WO 02/10092 cited hereinafter): Co is apparent from Figure 3 (which is a graphical representation of the delta L * and delta a * values of the previous tables 59 (1) and 59 (11)), an analysis of the delta L places * and delta a * according to the smoothed modalities obtainable with the prior art and obtainable according to the present invention shows that the delta a * positive values obtained, for example, for the increase reguerido in the redness, the respective values of delta L * obtained according to the present invention are negative, while those according to the prior art are positive. Rather, in the following Tables 59 (111) and (IV), a comparison of the data of L *, a *, b * was made, always between the smoothed modalities of WO 02/10092 and the smoothed embodiments of the present invention.

Table 59 (111): L * a * b * data according to WO 02/10092 (taken from the respective examples of WO 02/10092 cited hereinabove) Table 59 (IV): Data of L * a * b * according to the present invention (taken from the respective previous examples, cited later in the present) As it is apparent from Figure 4 (which is a graphic representation of the values of a *, b * and L * of the previous tables 59 (111) and 59 (IV)), the analyzes of the colorimetric data given In the present application and in the prior art, for the smoothed modalities, it is confirmed that the present invention allows the achievement of new colors in the range of coffee red to pink orange. This is true in particular for the red-brown colors not obtainable to date, which are suitable in the lower right part of the graphical representation of the a * vs. diagram. b * (Figure 4) showing two point clouds (one of the prior art and the other of the present invention), located in contiguous but nevertheless substantially different areas of the color space. It seems that a virtual line of distinction between the two colors could run from the lower left to the upper right, for example, approximately from (0/0) to (18/30)), thus dividing the pinkest tones of the most orange tones. On top of this, it should be noted that, even if it is not apparent from the two-dimensional graph of Figure 4, the L * values obtained according to the present invention are generally lower than those according to the prior art, which means that the two clouds depicted in Figure 4 are located substantially at different levels with respect to their projection plane shown in Figure 4. The generally lower L * values of the present invention mean, viewed from the eye of a human observer, that the respective colors are darker and more pronounced (for example, "stronger" than the generally clearer colors obtainable above, and thus more adapted for blending with additional chromophores.

EXAMPLE 60: Further comparative investigations by fine-tuning through different parameters, in particular the amount of chromophore ion, the nature of the chromophore ions, the amount of additive and the nature of the additive, both in the specific non-smoothed embodiments of the present invention and of the prior art. Using the same procedure and the powder for identical porcelain stoneware "(supplied by ARKIM) as in examples 1-58 above, and using the silica gel as in example 3 (Gr = 91.86%; A = 283.7 m2 / g, S = 260.6 m2 / g) and / or ZnO as additive, the following investigations shown in the following tables 60 (1) -60 (V) were carried out, In particular, in the following, the amount of ZnO is expressed as percentage by weight of Zn referred to the total ceramic mixture, which comprises aggregated ZnO In the tests according to the invention, aqueous solutions comprising 1% -10% of iron (expressed as elemental iron) were used on ceramic mixtures added with 1.53%, 5.26%, 8.70%, and 14.5% (expressed with respect to the dry ceramic mixture, eg, before mixing) of the silica gel additive as in Example 3. In particular, iron and aqueous ammonium citrate and chromium acetate were used as dye solutions, loaded with the percentages of chromophore ions reported in tables (I) - (IV) below. One or two drops of the coloring solutions (one drop weighing approximately 0.047 ± 0.005 g) were applied, in the same way as reported below. The samples and tiles (of which those containing ZnO were prepared in a metallic net support, to prevent the melting of the tile in the oven, due to the addition that decreases the melting), were cooked, this time, in an oven electric for laboratory with a 50 minute porcelain stoneware firing cycle (from cold to cold) at a maximum temperature of 1205 ° C. All the data reported below (including those according to the invention) have been measured on non-smoothed tiles, since the ZnO-doped patterns were nonetheless deformed to a degree that made it impossible to obtain a sufficiently uniform colored surface after smoothing.

Table 60 (I): Table 60 (11) Table 60 (111) Table 60 (IV) As it is apparent from the above tables, also testing (on non-smoothed modes) the use of different coloring compositions and different additives in varying amounts, the use of the specific silica additives according to the present invention leads to negative values of delta L * (for example of a decrease in L * with respect to the additive-free reference standard), while delta L * values are positive (for example, L * is increased with respect to the free reference standard of additive), if a ZnO additive such as WO 02/10092 is used.

It is noted that in relation to this date, the best known method for carrying out the aforementioned invention is that which is clear from the present description of the invention.

Claims (23)

CLAIMS Having described the invention as above, the content of the following claims is claimed as property:

1. A coloration process for obtaining on the surface and / or inside the baked ceramic material, a variation in the color resulting from the iron-based coloring solutions, characterized by: (a) the addition to the ceramic mixture of 1 % to 15% by weight with respect to the mixture of dry ceramic, precipitated silica and / or silica gel having an active surface S > 100 m2 / g at the moment of coloring, the active surface S is defined by the formula S = A * Gr, where: Gr is the fraction of particle size between 5 and 60 micrometers for the precipitated silica, and between 1 and 60 micrometers for silica gel, and A is the surface area of the silica expressed in m2 / g as measured by the BET method; (b) apply to the surface of the ceramic mixture containing additive, aqueous or organic solutions comprising inorganic salts of Fe (II) and Fe (III), or organic derivatives of Fe (II) and / or Fe (III); (c) the variation in the resulting color is equal to? E > 6.

The process according to claim 1, characterized by adding the ceramic mixture, precipitated silica and / or silica gel in a total amount between 2% and 10% by weight of the dried silica with respect to the dry ceramic mix.

3. The process according to claim 2, characterized by adding the ceramic mixture, precipitated silica and / or silica gel in a total amount between 3% and 7% by weight of the dry silica with respect to the mixture of dry pottery

4. The process for coloring ceramic materials according to claims 1-3, characterized by step (a) is implemented by the addition of precipitated silica and / or silica gel to the raw materials or to the piece.

5. The ceramic mixture containing additive, characterized by being obtained according to step (a) in accordance with one or more of claims 1-4.

6. The coloring process according to one or more of claims 1-4, characterized by using at least one ceramic mixture containing an additive, in accordance with claim 5, in inhomogeneous mixture together with additional ceramic mixtures. .

7. The non-homogeneous mixture of ceramic mixtures, characterized by at least one mixture comprising additives according to claim 5.

8. The process for coloring ceramic materials according to one or more of claims 1-4 or 6, characterized by the ceramic material and containing additive according to claim 5 or 7, is treated with aqueous solutions containing from 0.1% to 20% by weight of iron (expressed as elemental iron) in the form of inorganic salts of Fe (II) and / or Fe (III) or inorganic derivatives of Fe (II) and / or Fe (III).

9. The process for coloring ceramic materials according to one or more of claims 1-4 or 6 or 8, characterized in that the organic derivatives of Fe (II) and / or Fe (III) are salts and / or complexes with organic compounds chosen from the acetylacetone group; ascorbic acid; carboxylic acids of the general formula Rx-COOH and / or a sodium, potassium or ammonium salt thereof, in which Ri represents hydrogen, a benzene ring or an alkenyl or alkenyl group of 1 to 9 carbon atoms, possibly substituted with 1 to 6 groups -COOH, -OH-, -NH2 and / or -SH groups; amino acids of the general formula and / or the sodium, potassium or ammonium salts thereof, where R2 = -H, -CH3, in which X = -H, -CH3 and Y = -H, -OH where R3 and R4 may be the same or different from each other and represent hydrogen, an alkyl group of 1 to 4 carbon atoms possibly substituted with -OH, - (CH2) n -COOH groups where n = l-3, - (CH2) m-NH (2-k) - (CHR5-COOH)) k in which m = l-6 and k = l or 2, and where R5 = -H, -CH3, which X = -H, -CH3 and Y = -H, -OH.

10. The process for coloring ceramic materials according to one or more of claims 1-4 or 6, 8, 9, characterized by coloring the ceramic material containing additive, an aqueous solution of iron ammonium citrate is used. contains 0.3% to 20% by weight of iron (expressed as elemental Fe).

11. The process for coloring ceramic materials according to claim 10, characterized in that to color the ceramic material containing additive, an aqueous solution of iron ammonium citrate containing 1% to 20% by weight of iron is used. (expressed as elemental iron).

12. The process for coloring ceramic materials according to one or more of claims 1-4 or 6 or 8, characterized in that the coloring solutions are aqueous solutions containing iron (II) -ammonium sulfate, iron sulfate (III) ) -ammonium, iron (II) chloride, iron (II) perchlorate, potassium hexacyanoferrate (II), potassium hexacyanoferrate (III), hexacyanoferrate (II) ammonium.

13. The process for coloring ceramic materials according to one or more of the claims 1-4 or 6, 8-12, characterized by the color solutions containing iron in the form of inorganic salts of Fe (II) and / or Fe (III), or organic derivatives of Fe (II) and / or Fe (III) also comprise inorganic salts and / or organic derivatives of the metals selected from the group: Co, Ni, Cr, Ru, Au, Mn, Ti, Zn, Zr, Sb, V, W, PD or their mixtures.

14. The process for coloring ceramic materials according to claim 13, characterized in that the coloring solutions contain 0.1-18.2% by weight of iron (expressed as elemental Fe), with a maximum cationic concentration of 20%, and have a Weight ratio of Fe / Me between 15/1 and 1/5, where in the case of several metals other than iron, Me means the sum in weight of the concentration of the different metals.

15. The process for coloring ceramic materials according to claim 14, characterized in that the dye solutions contain 0.3-18.2% by weight of iron (expressed as elemental iron), with a maximum cationic concentration of 19.5% and have a ratio of Fe / Me weight between 13.9 / 1 and 1/5, where in the case of the different metals different from Fe, Me means the sum in weight of the concentration of the different metals.

16. The process for coloring ceramic materials according to one or more of claims 1-4 or 6, 8-15, characterized by the following operative steps: (a) adding precipitated silica and / or silica gel to the mixture ceramic to be molded in an amount between 1% and 15%, preferably between 2% and 10%, more preferably between 3% and 7% by weight of the dry silica with respect to the dry ceramic mixture; (b) molding the ceramic mixture; (c) drying the molded ceramic material; (d) treating the ceramic material derived from the preceding step with at least 2 g / m2 of coloring solution; (e) drying the ceramic material derived from the preceding step; (f) cook the ceramic material.

17. The process for coloring ceramic materials according to claim 16, characterized in that between step (c) and step (d), one or more intermediate steps (c ') of pre-treatment of the material are carried out. dry using water or aqueous solutions of mono- or poly-carboxylic acids or their salts.

18. The process for coloring ceramic materials according to claim 16 or 17, characterized in that between step (d) and step (e), one or more intermediate steps (d ') of post-treatment of the material are carried out. previously treated with the coloring solution, using water or aqueous solutions of mono- or poly-carboxylic acids or their salts.

19. The process for coloring ceramic materials according to claim 16 or 17, characterized in that between step (d) and step (e), one or more intermediate steps (d ') of post-treatment of the material previously treated with the coloring solution are carried out, using aqueous solutions of inorganic salts.

The process for coloring ceramic materials according to claim 18 and 19, characterized in that the step (d ') is carried out after the treatment with aqueous solutions comprising mono- or poly-carboxylic acids or their salts, as well as as inorganic salts.

21. The total or partially decorated ceramic material characterized in that it is obtained in accordance with one or more of the process variants described in claims 1-4 or 6, 8-20.

22. The ceramic material decorated according to claim 21, characterized in that the surface thereof has been subjected after firing to satinization, smoothing, polishing or burnishing.

23. The decorated ceramic material according to claim 22, characterized in that it is made of porcelain stoneware.