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Stains

We make no attempt to classify or compile stains available here, there are too many. Individual stain manufacturers offer huge ranges of different colors and color systems (the same color can often be made using different combinations of oxides, each having its own advantages and disadvantages). While there is a limit to how many separate colors can be made, there is not limit to the number of tones! The printed color charts from these companies can be intimidating to say the least and the companies have problems keeping their charts up-to-date with new products. While many substitution charts are available for frits from different manufacturers, the sheer number and range of stains makes this much more difficult. Remember, in ceramics, color as about chemistry, not just of the stain, but of the host glaze it is blended into, so things are a lot more complicated. In addition, new advances add new complexities (e.g. ink jet printing requires very high stability against disolution in the glaze melt, for example brown or yellow brown pigments having spinel structure and pink, turquoise, yellow, green stains having zircon structure, these are more stable than even silica or alumina).

It is difficult for manufacturers to match printed colors with the actual color of the stain, it is not unusual to have a stain fire darker than another when the printed color chart shows it to be lighter. Everyone knows that the same stain will fire differently in different glaze bases so nailing down an absolutely standard color on a data sheet is impractical. Some manufacturers offer product literature to explain the types of glazes (including the chemistry) each stain is intended for and they have technical staff on hand to assist customers. The technical staff in some companies will deal directly with small manufacturers or even individual potters. Other companies have very little support materials and sell only through their agents who explain the products to large manufacturing firms. The chemistry of many stains is widely known whereas the makeup of others is a closely guarded secret. While a chemical analysis can be done on a stain this may tell only part of the story since the sintered particles may have a physical structure that is a product of the way they were fired or other processing steps.

Stains offer many advantages over raw oxide colors (less toxic, color reliability, compatibility with various glaze chemistries and they do not have an LOI). Companies have developed numbering systems for their stains and over the years these numbers can change. Suppliers or even manufacturers often blend (and further process, e.g. grinding) products they buy from stain producers and sell them under new names for specific markets. The particle size of stains is often important to the task at hand. Some stains are washed with acid solutions. Quality control at all stages of production is obviously very important to maintain the color. There is a wide range of qualities of stains available (again quality generally refers to consistent particle dynamics and chemistry). The manufacturers using older equipment and processing methods have greater problems maintaining quality. Other companies have modern equipment but have not fully learned the importance of quality, sometimes a supplier will act as an agent (and even blender) between a manufacturer and users to assure quality.

The production of stains entails the usage of often toxic materials. Some manufacturers are taking advantage of less stringent environmental and workplace hazard regulations in third world countries to produce stains cheaper but sometimes with greater human cost to the local people and their land.

Links

Articles Formulating a Clear Glaze Compatible with Chrome-Tin Stains
In ceramics color is often a matter of chemistry, that is, the host glaze must be compatible and have a sympathetic chemistry for the stain being added. Chrome-tin stains are a classic example.
Articles Getting the Glaze Color You Want: Working With Stains
There are many things to know about to make the best use of stains, but one often ignored aspect is the relationship between glaze color and chemistry. If you want to control color you need to know about stains and chemistry.
Articles An Overview of Ceramic Stains
Understanding the advantages of disadvantages of stains vs. oxide colors is the key to choosing the best approach
Articles Glaze and Body Pigments and Stains in the Ceramic Tile Industry
A complete discussion of how ceramic pigments and stains are manufactured and used in the tile industry. It includes theory, types, colors, opacification, processing, particles size, testing information.
Hazards Zirconium Encapsulated Stains
Glossary Encapsulated Stains
This is a type of stain manufacture that enables the use of metal oxides (like cadmium) under temperature conditions in which they would normally fail.
Glossary Ceramic Stain
Ceramic stains are manufactured powders. They are used as an alternative to employing metal oxide powders and have many advantages.
Glossary LOI
Loss on Ignition is a number that appears on the data sheets of ceramic materials. It refers to the amount of weight the material loses as it decomposes to release water vapor and various gases during firing.

By Tony Hansen


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