ES2303783B1 - COLOR PROCEDURE IN COMMON GLASSES OF CALCICO SODIUM SILICATE BY THERMAL TREATMENT. - Google Patents

Abstract

Coloring procedure in common glasses of calcium sodium silicate by heat treatment that allows obtaining superficial colorations, transparent or not, in common calcium sodium glasses caused by thermal interaction of the base glass and mirrors or mirrored surfaces.

Description

Coloring procedure in common glasses of calcium sodium silicate by heat treatment.

Technical sector

The application sector of the present invention It is related to the coloration of common silicate glasses calcium sodium for preferably decorative applications or artistic.

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State of the art Colored glasses

A glass is colorless when hitting it white light, all the wavelengths that make up the light are They transmit in the same proportion. However, when the glass absorbs with different intensity and selectively some of the Wavelengths of white light will present an appearance colored, which is nothing more than the sum of the spectral components They pass through the glass. Most of the glasses are colorless, since its components are too. That's why it is necessary to incorporate substances or coloring agents to give rise to to a certain coloration. To these substances or agents responsible for the coloring in the glasses are called chromophores

Colored glasses can be classified according to the degree of dispersion of the chromophores they contain. Following an increasing order of size, chromophores can encompass from those who are in an intimate state of dissolution, with a degree of ionic or molecular dispersion (for example, the coloration due to the presence of iron ions, cobalt, nickel, chrome, etc; 1 nm chromophores size, approximately), to those that form crystalline aggregates of visually appreciable sizes (for example, the color of the Aventurite and hematinone glasses, due to the presence of metallic copper or chromium sesquioxide particles; size of chromophores greater than 100 nm). In an intermediate interval would be the colloidal size dispersions (for example, the coloration due to the presence of copper monoxide colloids, metallic silver, metallic gold, copper sulfoselenide, etc; chromophores size between 1 and 100 nm).

The largest group of chromophores is that of ionic dyes and most colored glasses are thanks to the presence of this type of chromophores. Not however all the shades of the spectrum can be obtained with the ionic chromophores. When the final application of the glasses colored has an artistic or decorative side are required special shades that are not always possible by conventional chromophores-based coloring procedures that dissolve ionically or molecularly in the mass of the glass.

The colored glasses by chromophores in state colloidal or microcrystalline are characterized by containing small clusters of atoms, whether metallic or nonmetallic, in zero oxidation state (elementary state) or in other states of oxidation. In this type of glass, the color evolves by subject them to heat treatment or annealing, unlike what happens in the colored glasses by ions or molecules, in the that the coloration only depends on the oxidation state of the chromophores Glasses colored by colloids or by Microcrystals are usually obtained as colorless or very glass weakly colored after obtaining by conventional fusion, to although there are already some dispersed nuclei in them that They will be responsible for the coloring. These glasses acquire their final coloration when they subsequently undergo a heat treatment and further cooling under conditions controlled. During that heating and cooling it has to reach a temperature range in which atoms or ions have adequate mobility to precipitate over the nuclei and form aggregates of chromophores that will be responsible for the final coloring Since aggregates are almost always formed by chemical species in its reduced oxidation state, it can be consider that this fact is a general characteristic of this group of colored glasses and, therefore, that are usually more or less intense reducing conditions are necessary for the adequate obtaining of the glasses.

Among the colored glasses with colloidal chromophores, the so-called Ruby glasses stand out, which owe their name to the intense red color that they present in different shades, depending on the particular nature of the chromophore and the particular experimental conditions of obtaining the glasses. There are ruby gold, copper and phosphor glasses that owe their coloring to the formation of colloids whose size ranges between 20 and 50 nm and that coexist with isolated microcrystals of 100 to 300 nm. The corresponding phenomenon of coloration in these glasses is due to the combination of two mechanisms: 1) the specific optical absorption of the colloids, and 2) the light scattering caused by the very small colloidal particles, as explained by the theory of Mie (G Mie, "Beiträge zur Optik trüber Medien, speziell kolloidaler Metalläsungen", Ann. Phys. 25 (1908) 3, 377-445).

The color of these glasses depends on the size of the colloids, so that increasing this size also grows the extinction coefficient and the absorption band moves towards longer wavelengths, which produces a more color browned When the diameter of the colloids or microcrystals increases until the wavelength of light is reached visible, in addition to missing the original color an appearance occurs murky that could become opaque for most cases extremes

Ruby coloring takes place through a process that can be divided into three stages: 1) ionic dissolution of the chromophore in the glass, 2) reduction of the chromophore to its state of lower oxidation or elemental state and 3) precipitation of chromophore and aggregation to form colloids or microcrystals.

The preparation of ruby glass mass or roughly thin layers of ruby glass on another base glass is a useful procedure to obtain special colorations, within from the range of red, orange and yellow, which are obtained very hard by conventional coloring procedures with  ionic or molecular type chromophores. The achievement of certain decorations on glass and / or effects on works of art Glass based would be greatly facilitated by coloring controlled by colloids of said glass materials. He interest in ruby glass has presented a historical constant, especially the ruby gold glasses and the ruby copper glasses, due to its attractive intense red color. His time of greatest splendor met in Venice in the late Middle Ages, when not only its color was appreciated but also some supposed magical virtues due to the conjunction of said coloration with the Made of containing gold in its composition.

Ruby gold glasses have been widely investigated In them gold dissolves in the mass of glass as Au + ions and subsequently, due to its high potential electrochemical, reduced to elemental gold during annealing to what is necessary for the glass to contain a reducing compound such as Sb_ {2} O_ {3}. A heat treatment after a temperature close to the softening of the glass favors the aggregation of gold atoms through a dissemination process that eventually leads to the formation of tiny colloids responsible for ruby coloring. He diameter of the colloidal gold particles that give rise to a suitable coloring should be between 0.01 and 0.10 micrometers, preferably between 0.02 and 0.05 micrometers. The colloids below that size do not produce appreciable coloration and above originate a turbidity (Tyndall effect) and a distortion of the red coloration. The necessary concentration of gold to produce ruby glass is between 0.005 and 0.05% by weight.

Obtaining the ruby gold glasses is subject to a series of experimental parameters difficult to check if you want to obtain a certain color, in addition to present the disadvantage of the difficult dispersion of gold in the vitrifiable mixture of the corresponding raw materials of glass.

On the other hand, ruby copper glasses are a Excellent alternative to ruby gold glasses and its color is equally much appreciated. In these glasses the color is produced by the dispersion of colloidal copper particles elemental and copper monoxide. In this type of glass there is the complexity of a redox chemical system in which the metallic copper atoms, the ions of Cu (I) (cuprous) and the Cu (II) ions (cupric). This makes it very difficult to predict the reactions that can occur in the glass when subjected to a  heat treatment that affects redox balances between different oxidation states of copper species. The appearance of the ruby coloration is explained by the dispersion of cuprous oxide in colloidal state. In a parallel way to what occurs in ruby gold glasses, in the first stage of the process copper dissolves in the glass melt and establishes a equilibrium between the three oxidation states of copper (Cu 0, Cu 1+ and Cu 2+). The relative proportion of these three oxidation states is what determines the development of the ruby color Said redox balance depends in turn on the partial pressure of oxygen, temperature and composition of glass

Since copper is less noble than gold, that is, it has a lower redox potential, its solubility in the glass is about forty times larger than gold and in an atmosphere Ordinary (air) dissolves as cupric ions (Cu 2+). The Reduction of these ions to a lower oxidation state requires reducing conditions much more energetic than the case of Ruby gold glasses. This reduction must occur during the glass fusion and is the second critical stage of the process of ruby color Usually and in an empirical way it is known that has resulted in the reduction of Cu 2+ ions to ions Cu 1+ when the blue hue of cuprous ions ceases to appreciate in the melt and begins to notice a weak coloration yellowish When the reduction is too energetic you can reach the formation of Cu 0 at the cost of all the copper present and Ruby color does not manifest after heat treatment of development. This treatment constitutes the third stage of process of obtaining the ruby coloration.

The relations [CuO] / [Cu_ {2} O] 1/2 and [Cu_ {2} O] ^ {1/2} / [Cu] are fundamental parameters in the development of coloration in ruby copper glasses and it depends on the partial pressure of oxygen that must be between 10 -13.5 and 10 -14.0 atmospheres. Under these conditions it produces the partial precipitation of elemental copper and the precipitation in greater proportion of the Cu 2 O that already coexist before developing heat treatment. During treatment developing colloidal aggregation of cuprous oxide occurs segregated from the glass and a growth of the microcrystals of elemental copper up to about 0.2 microns. When the heat treatment is prolonged, said crystals may exceed the size of 1 micrometer and finally coexist with the aggregates colloidal of Cu 2 O.

In practice the minimum concentration of CuO to obtain the ruby color it is estimated at 0.5% in weight. However, the most recommended proportion is 2% in weight. On the other hand, concentrations higher than would result in the appearance of large precipitated crystals, such as They are typical in hematinot glasses. As reducing agents during the melting, carbon dust, acid, is usually used tartaric, sugar or other organic compounds, or silicon, aluminum, tin or silicon carbide powder in proportions of 0.02 to 0.2% by weight.

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For similarity with the golden ruby and gold copper, the glasses that incorporate colloidal silver giving place to a yellow coloring are called ruby silver glasses or yellow ruby glasses. Your coloring is much appreciated, especially for decorative and artistic purposes since the shades that can be achieved are not easily accessible by other coloring procedures or by using ordinary ionic chromophores.

The incorporation of silver compounds in Glass originates the formation of silver colloids. The mechanism consists of a previous dissolution of Ag + ions in the melt of glass and a subsequent precipitation of silver as atoms metallic (Ag 0) that are added to form very small colloids in a similar way to what happens with ruby glasses of gold. In this case, the color obtained can vary. from yellow to reddish brown. The band of absorption presented by ruby silicate silver glasses places at 440 nm, but can travel up to 500 nm, resulting in a red color in the case of phosphate glasses.

Since silver is less noble than gold, the concentration of silver ions in solution that can admit a glass is larger (between 0.05 and 0.5% by weight). During treatment thermal development develops a yellow amber color that It ends up being gray if the treatment is long enough.

Ruby mass coloration does not present many advantages from a practical point of view, especially for Artistic or decorative applications. The procedures of obtaining are very critical, prolonged in time and tedious from the experimental point of view. Much more interesting is the obtaining superficial colorations in various shades of yellows that was already widely used since the Middle Ages to its application in the production of stained glass. Coloring Superficial by cementation is based on diffusion penetration of silver ions across the surface of the glass by a ion exchange mechanism with the alkaline ions of glass. The change is favored because the Ag + ion and the Na + ion They have the same load and a very similar size. The process takes out by dipping the glass in a salt of molten silver or coating the glass with a paste prepared with a material inert (clay) agglomerated with an oil to which the silver compound The proportion of silver can vary between 5 and 20% by weight. Then the glass is subjected to a treatment thermal at a temperature slightly below that of deformation of the glass This process allows the migration of Ag + ions, the progress of which depends, according to the laws of the diffusion of the respective concentrations of the ions that are diffuse, of the temperature and the treatment time. The thicknesses of the colored layers that can be obtained oscillate around 100 micrometers Subsequently the Ag + ions are reduce to elemental silver (Ag 0) by treatment thermal to be carried out in a reducing atmosphere, to facilitate the reduction of silver and its aggregation to colloids that when they grow they give rise to yellow coloration.

This experimental procedure has been used as a decorative technique because it allows to obtain drawings in the surface of the glass pieces and alternate colored areas with colorless areas, removing in these the thin layer colored by carved or acid etched. It is also used to perform recordings, inscriptions, graduation strokes, etc. in glasses laboratory technicians, as well as to produce glass with conductive coatings and glass with reflective films of single face

By a procedure analogous to that described for the silver surface ruby coloration, can also be obtained superficial red copper colorations. First it takes place the diffusion of cuprous ions from a compound of copper dispersed in the paste applied on the glass objects and subsequently its reduction and thermal development of the ruby color This technique is widely used in the News for the decoration of artistic glass with very effects Decorative With copper you can also get a color black surface when precipitated in the form of sulfur. For it the glass is coated with a paste containing about 50 to 75% cupric sulfate and undergoes a first treatment thermal that results in a greenish color. Then the glass is count in a reducing atmosphere to develop coloration black

As previously mentioned, there are other glasses colored by microcrystals that are included in the group of aventurine and hematinot glasses. Can be consider as a particular case of ruby glasses and in them the coloring is due to the presence of crystals of size appreciable that are formed by slow cooling of the vitreous mass. Aventurite copper glasses are characterized red glasses for the metallic reflection and shine that gives them a uniform dispersion of copper crystals in the form of sheets hexagonal, octahedron or rhombohedron with a diameter between 0.1 and 1 mm. They are obtained from compositions glass with a cupric oxide ratio greater than 5% (much greater than in ruby copper glasses). The merger is done in moderately reducing atmosphere. At temperatures above 1100 ° C copper is dissolved in the cuprous glass and iron which is usually added as a reducer, in ferrous form, so that during cooling the balance between these two redox species gives rise to metallic copper and ferric oxide. In this way they form metallic copper crystals that can easily grow by diffusion until reaching the indicated dimensions. Although most of the copper aventurine glasses are formed by crystals of metallic copper, there are also aventurine glass formed by large light red and matte dendritic crystals cuprous oxide that can be obtained from compositions alkaline rich in lead oxide and free of iron oxides and  tin, when melted in a reducing atmosphere and allowed to cool very slowly.

Copper hematinot glasses differ of the copper aventurine in which the copper crystals that they contain are much more numerous and considerably smaller, with a size of about 0.5 micrometers, that is, three orders of smaller magnitude Its dimensions make the glasses opaque but they do not provide metallic reflections. The small size of these crystals are achieved by cooling the glass more quickly, which causes abundant crystalline nuclei to form developed by subjecting the glass to a heat treatment later.

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Glass Staining Techniques

The glass coloring techniques that make use of transparent glasses, colored by immersion in a bathroom, either by casting, or more frequently, extending with brush or more easily by immersion, a veil of color on the Glass surfaces are known for many years. Unfortunately, these techniques do not allow certain shades of colors for special decorative applications or for the production of glass art, especially for the creation of sculptural works. They are summarized below. some techniques already known about special coloring of glasses

According to patent 275372 of the Compagnie Saint Gobain (France) of 1962 it is possible to color glass sheets obtained according to the casting procedure on a tin bath or of molten tin alloy, applying on the face of the sheet of glass that is in contact with the tin or alloy of tin an aqueous solution of an easily reducible metal salt monovalent, and then, after having separated the water by evaporation, taking the glass sheet for a few minutes coated with the saline tank at a temperature of the order of 600 to 700 ° C This avoids the classic cementation process with silver salts, for example, to produce a yellow coloration superficial. It also has the advantage that it is not necessary to carry carry out a heat treatment in a reducing atmosphere to ensure the reduction of metal salt. By this procedure they are obtained colored layers with different shades depending on nature of the salt of the solution used.

According to patent 425129 of Glaverbel-Mecaniver., S.S. (Belgium) of 1974, it You can color or modify the coloring of a glass body causing a substance to diffuse inside the layers surface of the glass body from a contact means, of so that during the formation of said body or after it introduces a reducing agent into the surface of the body; because a treatment medium comprising at least a salt that supplies reducible silver ions by the agent reducing agent and a diluting agent consisting of one or more salts of other metal or metals, with an electrical potential between -600 and +300 mV. The experimental procedure is carried out at a suitable temperature for silver ions to diffuse from the half to the glass body and there be reduced by the aforementioned reducing agent. The color that is obtained by this procedure is based on a mechanism of ionic change and is in the range of yellow.

European patent 88112269.1 of the company Frenzelit Werke GMBH & Co. (Germany) of 1988, on a dyeing procedure of silica glass fibers and articles textiles thus produced explains that this is possible with the help of organic dyes by treating with glass acids possibly decoupling, coloring and eventually application subsequent of a sizing preferably watertight Water.

European patent 91110453.7 of the company PPG Industries, Inc. (USA) of 1992 on transparent glass colored on the edge explains the procedure to produce Highly transparent glass with a light blue border color pure, which presents a pleasant appearance and offers a alternative not previously available for furniture applications and the like The effect is achieved by the use of very large amounts. small iron oxide (proportions less than 0.02% in weight, expressed as Fe 2 O 3, the iron ratio being present in the crystal in the ferrous state, expressed as FeO, with respect to the total amount of iron in the crystal, expressed as Fe 2 O 3, at least 0.4) as the only essential dye. The use of cerium oxide or secondary dyes, such as as cobalt oxide, thus providing a more color pure and maintaining very high visible light transmittance.

Francesco European Patent 99830026.3 Langella (Italy) of 1999 on an industrial procedure of glass coloration and surface concentration of oxides dyes aims at a means and a coloring technique  surface glass of economic type of coupling, by fusion of glass, in economical transparent glass, by means of screen printing, or any other process, of a vitrifiable and transparent coloring composition whose temperature It is close to the melting glass. In this case the object of the  invention consists in avoiding all the inconveniences of previously mentioned techniques and propose a technique that allows separate the concept of melting and lamination of glass paste for the production of flat, transparent, glass corresponding to the color of the glass and, at the same time, propose a technique that guarantees, conveniently, better results, and that provides the possibility to the producing house of colored printed glass, to produce only glass colorless, in order to minimize production costs. Specifically it consists of a technique that provides the possibility of concentrating on the surface part of the glass, an amount of coloring oxide that allows to obtain chromatic results similar to those of colored glasses in paste, and thus apply this procedure downstream of the large facilities of glass fusion and lamination, with great advantages also both from the economic point of view as of the flexibility of production. The technique of flat glass coloring is possible by fixing and concentrating on a glass surface of a thin layer of amalgamated paste consisting of suitable coloring and melting oxides, vitrifiable to the softening temperature or, in summary, melting glass surface.

Object of the invention

The present invention relates to obtaining surface colorations, transparent or not, in common calcium sodium glasses caused by the thermal interaction of the various vitreous materials involved: the base glasses themselves and the mirrors. A mirror is a common glass that includes what is called a mirror layer that contains the chemical elements necessary to provide a highly reflective face when the mirror is viewed from the opposite face.

The interest of the present invention consists in get colorations in the range of yellow, sand and roasted in a superficial way in glasses, without using chromophores Conventional ionics or any other type of glass additions You want to color. On the other hand, it is interesting to take advantage of possibilities of surface coloring procedures that they have been known for many years, in the sense of producing Ruby-colored colloids based on dispersed colloids in a vitreous matrix With this invention colorations are obtained particularly useful in glass decorations with purpose artistic and / or decorative, and is valued in a special way as practical application for the elaboration of sculptural works in glass where the coloring is caused without the contribution of any specific chromophore For this, a procedure has been developed which allows to have superficial ruby-colored colorations in glasses in a simple and easy to control way. Saying procedure is also characterized by taking advantage of the elements potentially chromophores that exist in the mirror layers of the common mirrors that will also be part of the work of glass art

In this way there are a number of advantages Practical order listed below:

one-

be You can get a ruby-colored coloration due to the existence of dispersed colloids in the glass.

2-

the coloration can be obtained in a glass layer instead of Obtain in all its mass, with what the artistic possibilities or of decoration multiply to be able to make drawings, engravings or markings removing the areas of the colored layer that interest

3-

It is not it is necessary to use chromophores additives for glass since the coloration is superficial and can be obtained in a localized way The desired areas.

4-

It is not it is necessary to have different crucibles or any other device to handle the different colors to obtain.

5-

be They can take advantage of common mirrors with a double purpose: use them as a constituent part of the glass work of art and as a source of chromophores for the base glass. Such chromophores are those that are included in the corresponding mirror layer of the mirror.

6-

be they can elaborate sculptural works in a single thermal stage in the which simultaneously integrates the mirror as a constituent part and the desired surface coloration occurs.

7-

he coloring procedure by controlled heat treatment Is it that there are several "thermal" forms? goes to moderate temperatures with consequent savings energetic.

8-

he procedure allows to apply these colorations in pieces of relief or exempt.

9-

he Coloring process is fast and simplifies artistic works  intermediate in obtaining color and texture.

10-

he result of the application of the procedure herein invention defines impossible plastic mass results to obtain by other traditional methods.

eleven-

the coloration obtained differs from those known and can be varied properly manipulating the interactions that consolidate in the vitreous mass in the process of obtaining the artistic work, in your case

12-

he procedure allows to reuse common glass materials from recycling (both base glass and mirrors), so the cost of the starting materials is very reduced.

Explanation of the invention.

The glass coloring process proposed in The present invention is carried out in the following phases:

one.

Preparation of the base glass and the components to integrate.

2.

Programming of the scheme heating-cooling according to the desired color characteristics in an oven or device similar heating.

3.

Baking process

Four.

Rapid temperature drop to the critical zone of glass cooling.

5.

Stable cooling control of the finished piece to room temperature.

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In detail, the indicated phases would be the following:

one)

Preparation of the base glass and the components to be integrated : the preparation of the starting materials that will be integrated into the sculptural work consists of scrupulous cleaning. Said cleaning can be carried out with a degreaser, distilled water, alcohol or ammonia diluted to 70%. In order to ensure proper cleaning, it is advisable to degrease the glass before and after cutting the pieces and fragments to be integrated into the sculptural work. The pieces are cut using conventional glass tools. After the final degreasing, the pieces and fragments of both base and mirror glass are arranged properly, placing the mirrored material, preferably between two pieces of glass (Figure 1) or under a piece of glass, with the lacquer Silver nitrate in contact with said piece of glass. During the handling of the item to be baked and its introduction into the oven, any type of contamination will be avoided, especially contact with common dust. Therefore, it is advisable to perform this stage in a room equipped with a smoke and dust extractor, as well as manipulate the pieces and fragments of glass and the sculptural precursor with gloves, preferably of lint-free fabric or fibers and any other type of waste.

2)

Programming of the heating-cooling scheme according to the desired coloring characteristics : the programming of said scheme (Figure 3) is carried out according to:

to)

the characteristics of the elements (dimensions of the pieces and glass fragments, their thickness and spatial arrangement).

b)

he type of oven to use (chamber dimensions, if available heating in hearth, vault or both and type of system lateral opening, upper or lower, and if gradients occur thermal inside the oven).

3)

Baking process: this process requires a good knowledge of the behavior of the distribution of temperatures inside the oven and whether increasing or decreasing thermal gradients occur. Preferably, an oven without thermal gradients or with a small decreasing thermal gradient (approximately -1 ° C / cm, a maximum of 10 cm) will be used, in the sense of its opening system. During the baking process, the fusion of glass and mirror pieces and fragments takes place until a single integrated element is formed. This element forms the piece of glass itself and is characterized by the rounding of the surfaces (due to the process of thermal softening of the pieces and fragments of glass) and the perfect integration of the components as a result of the adhesion produced between the different pieces and constituent fragments, as a result of the thermo-viscous flow of the glasses (Figure 2). It is essential for the correct fusion that the different pieces and fragments of glass that are thermally compatible with each other. That is, they have the same or similar coefficient of thermal expansion. The value of the thermal expansion coefficients of the glasses and mirrors (of calcium sodium silicate) that are used for the elaboration of the sculptural precursor should preferably be between 8.5x10-6 and 9.0 x 10- 6 K-1 (mean expansion coefficient, measured between 20 ° and 500 ° C). In any case, the difference in the coefficients of thermal expansion of the different glasses and mirrors that are used must be less than 5x10 -7 K-1, in order to guarantee the correct fusion of the different pieces and fragments that compose it.

4)

Rapid lowering of the temperature to the critical cooling zone of the glass : once the temperature necessary for the softening process of the pieces and glass fragments is reached (Figure 3), a rapid lowering of the temperature is caused, in order to avoid the devitrification of the glasses (This temperature is usually around 550 ° C). To do this, it is sufficient to open the oven door for the necessary time, which will vary depending on the maximum temperature reached and the volume of the elements introduced. This opening time represents 1% of the total process time. The phenomenon of devitrification occurs when the glass remains static at high temperatures inside the oven, the most visible consequence being the loss of vitreous properties and amorphous character and the evolution to a crystalline state. Therefore, it is necessary to reduce the time that the glass elements remain at high temperatures.

5)

Stable cooling control of the finished piece : the final period includes the total cooling of the sculptural piece and consequently its thermal and mechanical stabilization. This is achieved according to the final section of the heating-cooling scheme, which, depending on the case, is obtained by thermal inertia until the ambient temperature is reached or by properly programming the cooling times.

Chemical physical mechanism of superficial coloration

The physical mechanism is explained below. surface coloring chemical produced in glasses that integrated into the sculptural work through various examples corresponding to the samples analyzed in the laboratories of the National Center for Metallurgical Research (CSIC).

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1. Analysis of the pieces and fragments of glass and mirror integrated in various sculptural works

The following table shows the results. obtained by x-ray fluorescence of the composition glass chemistry and mirrors integrated in the works Sculptural studied.

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one

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These results indicate that the glasses analyzed, both from the fragments used and base glass, like those from mirrors have a chemical composition corresponding to sodium silicate glasses Conventional calcium As can be seen, the intervals of variability of the contents of the constituent oxides of the glasses are wide enough to show that in the surface coloring process that is developed here invention can be used as starting materials a wide range of conventional glasses of the sodium silicate type calcic.

The chemical composition of the mirrors is evaluated by X-ray scattering energy analysis at through scanning electron microscopy. These analyzes are performed on the surface of the mirror samples on the face where the mirror layer was. The following table shows collect the results obtained.

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2

3

In order to complete the characterization of the mirrors were made X-ray diffractograms of the themselves, which could show the presence of crystalline phases Some examples of the crystalline phases detected are summarized in the following table.

4

These results indicate that the composition The chemistry of the mirrors is based on oxides, simple or mixed, of various metals, since the oxygen contents are high. He calcium appears in the form of calcite and / or vaterite, that is to say as carbonates and their presence is attributed as the basis of the mixture for obtain the mirror, with which the other oxides of metals that play an active role in the function highly mirror reflective. Also, the metallic elements Majority are, for example, Ca, Ti and Ba in mirror 1; Ba, Zn and Pb in mirror 2; and Ca, Ti and Ba in the mirror 5. A study detailed of these chemical compositions reveals the presence of calcium salts (and magnesium in a smaller proportion, except for mirror 2 in which higher content of magnesium than calcium), silicon oxide and aluminum (this last always in smaller proportion), titanium oxide (especially abundant in mirror 1), barium oxide (especially abundant in mirrors 1 and 2), lead oxide (only present in mirrors 2 and 5 and mostly in mirror 2), zinc oxide (with relatively high concentrations in mirrors 1 and 2 and absent in mirror 5), iron oxide (only present in small proportions in the mirror 5), and sulfur and bromine that they can come from the organic phase (polymers, oils, paints) used as a binder for the preparation of mirrors. From this result set can be deduced that the composition chemistry of the mirrored elements is capable of causing a suitable coloring by the procedure described in this invention must contain metal oxides such as titanium, barium, zinc and lead, whether all simultaneously or not. In any case the average overall content of said metals so that the coloring process will be between 16 and 46% by weight, being 30% preferable by weight. The essential element of mirrors, which is the last responsible for activating the desired coloration in sculptural works, it is copper whose presence in very small proportions will determine, under the conditions of oxide-reduction favored by the other oxides of metals present in the mirror, the type coloring mechanism Ruby. In some cases, as in the sample of mirror 4, copper surely it is in very low concentrations below of the detection limit of the X-ray diffraction technique used in its characterization. However, the fact that has produced coloration indicates, undoubtedly, that very tiny copper concentration is sufficient to activate the coloration by forming nanocoloids, as demonstrated in the next section by microscopy observations Transmission electronics

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2. Physical chemical characterization of the particles nanometrics (colloids) responsible for coloring in various sculptural works

The microstructural characterization and morphological of the nanocoloids responsible for the coloration of the sculptural works studied as examples, as well as their Qualitative chemical composition were studied by microscopy Transmission electronics The experimental technique used was the one of direct replica of the colored surfaces, coming from a fresh fracture of the corresponding glass sample, previously attacked gently with hydrofluoric acid vapors diluted (5% in vol.) for 1 min. With the aforementioned technique, had a set of samples for observation in the electron microscope that allowed to take numerous micrographs Increases at which micrographs were taken They varied between 20,000 and 300,000.

In the fields observed and photographed from the various samples studied (in turn belonging to different sculptural works), the coexistence of isolated nanocoloids and nanometric particles grouped irregularly in terms of aggregation level and grouping morphology. In some areas less representative, that is to say that they appear less frequently, observe accumulations of particles that appear as spots of size larger than nanometric. On the contrary there are also little areas  representative where colloids are of a very small size (less than 10 nm) and appear very scattered. Therefore, the arrangement of the particles responsible for coloring in the glass sine conforms to a wide distribution of sizes ranging from 10 to 300 nm, depending on the level of aggregation of the colloids. The largest nanoparticles are formed by grouping of smaller particles. Scientific studies background on superficially colored glasses by Metallic nanocoloids indicate that more yellow colorations pure are due to the presence of nanometric particles that produce absorption in the visible spectrum, around λ = 410 nm. This optical absorption is due to resonance of superficial plasmons of metal colloids. The color that is obtained is all the more pure and intense the more narrow is the size distribution of the nanocoloids involved in the coloring process. That is, if they are generated metal colloids of similar sizes and are arranged in a way as regular as possible on the surface of the glass, either isolated or in addition.

The electron microscopy study of transmission also allowed to analyze the chemical composition qualitative of the nanocoloids responsible for color in the works sculptural These analyzes were performed with an analytical probe X-ray coupled to the electron microscope. The spectra that are obtained from colloids from different samples and different areas demonstrated the presence of Ca, Cu, Al and Fe. Between these detected elements is exclusively the Cu that can form metallic nanocoloids, which in turn activate the coloration by the mechanism of resonance of superficial plasmons.

As described in the section on bibliographic background, copper colloids impart a surface coloration in conventional sodium silicate glasses calcium that can vary between light yellow and deep red, depending on its size and state of aggregation. The coloring is produced by the dispersion of colloidal copper particles elemental and copper monoxide. The control of the generation of copper nanocoloids with the appropriate size and aggregation for produce the desired color in the sculptural works is done through the heat treatment described above.

Description of the figures

Figure 1.- Scheme of preferential placement of the mirror, E, between two pieces of glass, V, on the base of the oven, B.

Figure 2.- Scheme showing the result after in baking. E represents the mirror or mirror surface, V represents pieces of glass and B represents the base of the oven.

Figure 3.- Example scheme heating-cooling of the baking process. T indicates Temperature in ° C and t indicates time in hours.

Claims (6)

1. Procedure of coloration in common glasses of calcium sodium silicate by heat treatment characterized by using mirrors or mirrored surfaces and glass to obtain the appropriate coloration. 2. Glass coloring procedure Common sodium calcium silicate by heat treatment according to previous claim comprising a baking process that allows the fusion of glass and mirror pieces until form a single integrated element. 3. Glass coloring procedure Common sodium calcium silicate by heat treatment according to previous claims comprising the following phases:

to.

Preparation of the base glass and the components to integrate.

b.

Programming of the scheme heating-cooling according to the desired color characteristics in an oven or device similar heating.

C.

Baking process

d.

Rapid temperature drop to the critical zone of glass cooling.

and.

Stable cooling control of the finished piece to room temperature.

4. Procedure for coloring in common glasses of calcium sodium silicate by heat treatment, according to claims 1, 2 or 3, characterized in that a mirror or mirrored surface is placed between two pieces of glass to obtain the appropriate coloration. 5. Procedure of coloring in common glasses of calcium sodium silicate by heat treatment, according to claims 1, 2 or 3 characterized in that a mirror or mirrored surface is placed on a piece of glass, with the silver nitrate lacquer in contact with said piece of glass, to obtain the appropriate coloration. 6. Procedure of coloration in common glasses of calcium sodium silicate by heat treatment, according to any of the preceding claims characterized in that the different pieces of glass used are thermally compatible with each other.