GB1577081A - Decoratively glazed ceramic articles - Google Patents

Abstract

Effect or reaction glazes have been produced with the aid of additives in the form of pigment agglomerates by pasting finely ground pigment particles with a hydrophilic liquid and subsequently suspending the paste in the base glaze. Screen-printing media are particularly suitable as hydrophilic liquids. With the aid of this process, the artist is provided with a means of producing, in ceramics, novel designs in glazes containing embedded crystals which also have corresponding aesthetic properties.

Description

(54) DECORATIVELY GLAZED CERAMIC ARTICLES (71) We, ROSENTHAL AG., a German Company, of 8672 Selb, Postfach 1520, Germany, do hereby declare the invention, for which we pray that a patent may be granted to us and the method by which it is to be performed, to be particularly described in and by the following statement: This invention relates to methods of decorating ceramic articles with glazes which are fired on at high temperature. Depending on the intended use of the articles, their glaze decorations should not only be hygienic, but should also impart a suitable beauty to the surroundings.

Decorative ceramic articles can be obtained with transparent, opaque, matt and crystalline glazes. Special effects are achieved when various types of glazes and colours lie completely or partially on top of one another, and these are therefore also called effect glazes. In contrast, glazes reacting particularly strongly with one another which are often pre-fritted, are also described as reaction glazes.

There are other glazes, coloured predominantly by iron oxide, which are often used in modern artistic ceramics. The frequently varying colourings and surfaces of such glazes, that is those containing iron oxide, are due to variations in the level of the iron oxide contents, the composition of the glaze, the nature of the firing and the way in which the glaze is applied. The iron oxide is incorporated in the glaze as a colouring constituent, colour tones of yellow, red and green to black being obtained. Moreover, in the manufacture of white ware, so-called iron spots or specks are formed by iron compounds which are irregularly distributed in the glaze as coarse grains. Such specks may also be produced by colouring or staining silicates, titanates, or silicon carbide compounds.They are generally undesirable in the manufacture of crockery or pottery, however, affected articles being regarded as rejects.

Such specks have nevertheless recently become of interest for decorative purposes.

Thus, it has already been proposed in German Laid-open Pending Patent Application 2 318 241 to add iron particles or other metal particles to the body materials of ceramic articles, the fired body then being coated with a suitable transparent glaze so that the ceramic article is given a decorative appearance. Another possibility is to add raw materials which melt out of the ceramic body, in particular raw materials which have a high iron oxide content such as, for example, lava, basalt, pyrite, or slags. These raw materials must not, however, be finely ground.

All these glazes are influenced by every variation in the firing temperature, in the mixture and also to the method of application. Consequently, these glazes are by nature very unstable and this often leads to a varying appearance of the surface of the glaze as regards colour and texture. Industrial application of such glazes with consistent results over a lengthy period is thus not generally possible.

The problem underlying the invention, therefore, is to produce ceramic articles decorated with aesthetically pleasing glazes which are fired onto the body at high temperature. More particularly, the problem is to suspend colouring agglomerates in the form of drops or flakes in a normal aqueous glaze so that they do not dissolve, but are distributed uniformly therein and appear in the fired glaze as coloured interspersions. The fired glaze should be particularly suitable for ceramic articles which are hollow.

A method of decorating a ceramic article, according to the present invention, comprises forming one or more finely ground colouring substances into a paste with a hydrophilic liquid, stirring the paste into an aqueous glaze so that the paste breaks up to form a suspension of agglomerates which amount to between 0.1% to 50% by weight of the aqueous glaze, applying the aqueous glaze with its agglomerate suspension to a ceramic article and firing, the agglomerates then appearing as a non-homogeneous distribution of coloured interspersions in the fired glaze.

It will be appreciated that altering the amount of the agglomerates in the aqueous glaze will lead to different decor effects. It is possible, for example, to obtain agglomerates each with a size of up to 10 mm. Indeed, the interspersions may then merge to produce striae in the fired glaze. It will also be appreciated that the aqueous glaze with its agglomerate suspension may be applied by immersion, spraying or any other convenient method.

In addition to cheapness, the hydrophilic liquid should have specific hydrophilic technical characteristics - certain screen printing media, for example, being very suitable in that they even enable different glaze suspensions to be kept dispersed from one another.

Further features and advantages of the present invention will appear from the following description of an Example thereof.

Finely ground colouring substances, such as previously dried glazes, are made into a paste with a hydrophilic liquid. This paste is then suspended as agglomerates of drop or flake form in a conventional aqueous glaze.

The ratio of the hydrophilic liquid to the colour carrier, and the viscosity of the paste to be stirred in, determine the shape and the size of the agglomerates in the aqueous glaze.

The intensity of stirring also affects the size of the agglomerates, and thus the size of the interspersions, longer stirring resulting in smaller agglomerates. In addition, the higher the proportion of the hydrophilic liquid, the smaller the agglomerates become. Conversely, the smaller the proportion of the hydrophilic liquid, the larger the agglomerates become - with about 10 mm appearing to be the upper limit.

Colouring substances can be divided basically into three groups:1. Those which have the same melting temperature as, or a somewhat lower melting temperature than, the aqueous glaze. Such substances result in interspersions with blended indefinite contours giving a flow glaze effect. In particular, frits or colour fluxes should be mentioned here, as well as specially prepared colouring substances obtained by adding fluxing materials to stains. These fluxing materials may be feldspars, glazes and frits. In this way the result is achieved that the interspersions are suitable for the firing temperature of the aqueous glaze and lead to a smooth surface on the ceramic article.

2. Those with a higher melting temperature than the aqueous glaze, which are thus not dissolved or are only partially dissolved at the glaze firing temperature. In this case more sharply defined boundaries are obtained for the interspersions which lead to the glazed surface being less smooth. As colouring substances under this group come in particular metallic oxides, spinels and ceramic stains, either alone or in combination.

3. Those which react chemically with the aqueous glaze at the glaze firing temperature and, reinforced thereby, produce interesting surface effects known as reaction glaze effects. In this case, materials which are not necessarily coloured before their reaction during firing with the aqueous glaze such as titanium oxide, calc-spar and silicon carbide should particularly be mentioned.

The hydrophilic liquids may be special oils which are employed primarily for other duties. What is important is that they are not water-repellent i.e. that they are able to wet and envelop a dry colour carrier powder well so that a more or less viscous paste can be mixed. Moreover, the adhesion of the hydrophilic liquid to the colouring substances must remain greater than the adhesion to the water of the aqueous glaze, after the paste has been stirred into the latter, so that the agglomerates in the aqueous glaze are preserved and do not coagulate with one another.

The production of an interspersion glaze in accordance with the above Example is effected by first preparing an aqueous glaze in conventional manner for the normal glaze firing temperature ranges. The weight per litre, the fineness of grinding, and the settling behaviour, are determined in accordance with normal industrial glazes. The colour of this glaze forms the base or ground colour in which the interspersions are to appear later in variable amounts, colours and/or sizes on the ceramic body after the firing. The forming of the one or more finely ground dry colouring substances into a paste is effected with a hydrophilic liquid, for example Blythe screen printing oil 63/15. The stirring of the paste into the aqueous glaze may be effected manually or by means of a stirrer. Moreover, as many different colour pastes as desired may be introduced into the same aqueous glaze. The finished glaze mixture is then worked up normally, before being applied to a ceramic article and then fired.

An infinity of decorative possibilities for ceramic articles is obtained in accordance with the present invention, especially in the fields of crockery, utensils and gift articles.

Depending on the particular field of application and aesthetic taste, the desired or required effect can be modified within wide limits by varying the composition. The demands of artists for more novel decorative media are moreover met with the abovedescribed interspersion glazes. Besides this, such glazes are not only simple, but are also cheap to produce since above all no great, technical complexity is required. Moreover, a means of replacing the so-called flow glazes is placed in the hands of the technician. Flow glazes, in fact, have the disadvantage - as the name already indicates - that during the firing they often flow down onto the firing support. Such an occurrence then generally results in rejects.Above all, however, the same aesthetic effects as with effect and reaction glazes can be achieved without having to apply a plurality of glaze suspensions beside and over one another. In this way, the application technique becomes simple and cheap.

WHAT WE CLAIM IS: 1. A method of decorating a ceram article comprising forming one or more finely ground colouring substances into a paste with a hydrophilic liquid, stirring the paste into an aqueous glaze so that the paste breaks up to form a suspension of agglomerates which amount to between 0.1% to 50% by weight of the aqueous glaze, applying the aqueous glaze with its agglomerate suspension to a ceramic article and firing, the agglomerates then appearing as a nonhomogeneous distribution of coloured interspersions in the fired glaze.

2. A method according to claim 1, in which said colouring substances are at least partially constituted by metallic oxides, spinels and/or ceramic stains.

3. A method according to either preceding claim, in which said colouring substances are at least partially constituted by reactive materials which react chemically with the aqueous glaze during firing to form the coloured interspersions.

4. A method according to claim 3, in which the reactive materials are titanium oxide, calc-spar and/or silicon carbide.

5. A method according to any preceding claim, in which said colouring substances are at least partially constituted by materials having generally the same melting temperature as the aqueous glaze.

6. A method according to claim 5, in which the materials having generally the same melting temperature as the aqueous glaze are colour fluxes, frits and/or stained glazes.

7. A method according to any preceding claim, in which said hydrophilic liquid is constituted by a screen printing oil.

8. A method according to any preceding claim, in which said agglomerates each has a size of up to 10 mm.

9. A method according to claim 1 and substantially as hereinbefore described.

10. A ceramic article when decorated by a method in accordance with any precedig

Claims (1)

1. claim.