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On the left are pure blue stain brush strokes, on the right are green ones (both painted over a glaze). Clearly, the green is refractory, stiffening the glaze enough to trap bubbles and sit on the surface as a dry, unmelted layer. The blue is the opposite, melting and bleeding profusely into the glaze. Under the glaze, these problems would be magnified (the blue bleeding more, the green causing crawling and blistering). Stains are not ceramic, they are ceramic additives. Stains are not safe for direct food contact. Stains are expensive. Stains don't suspend in water, paint poorly and dry as a lose powder. These stains each need to be added, as a minor percentage, to a ceramic painting medium (one with CMC gum and a mix of ceramic materials tailored to melt to the desired degree and have a compatible chemistry for develop the color (as per manufacturer guidelines).
The logo on the left was rubber-stamped using and ink mix made of only glycerine and Mason 6666 black stain. The glaze is shedding off during firing. Multiple properties needed by a stamping ink are not present here. First, the stain dries as a powder, it has no hardening or bonding properties, glycerine is its only mechanism. Second, it is too concentrated, the black color is so powerful that it bleeds excessively into the overlying glaze. Third, it does not melt during firing so it does not bond with the body below. And, it either develops only a fragile interface with the glaze above, or sheds it off. The piece on the right mixes the stain 50:50 with a glossy transparent glaze, from that it inherits better lays down, accepts the overglaze better and dries harder. Black stains are potent, an 80:20 stain:glaze mix would work even better.
Articles |
An Overview of Ceramic Stains
Understanding the advantages of disadvantages of stains vs. oxide colors is the key to choosing the best approach |
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Glossary |
Overglaze
A method of applying decoration over the glaze surface of ceramics. It can be done before or after the glaze firing. |
Glossary |
Flux
Fluxes are the reason we can fire clay bodies and glazes in common kilns, they make glazes melt and bodies vitrify at lower temperatures. |
Glossary |
Refractory
In the ceramic industry, refractory materials are those that can withstand a high temperature without deforming or melting. Refractories are used to build and furnish kilns. |
Glossary |
Ceramic Stain
Ceramic stains are manufactured powders. They are used as an alternative to employing metal oxide powders and have many advantages. |
Troubles |
Bleeding colors
In ceramics, the edges of overglaze and underglaze color decoration often bleeds into the over or under glaze. How can this be avoided. |
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