Why you should not paint pure stain powders over glaze

On the left is a pure blue stain, on the right a green one. Obviously, the green is much more refractory. On the other hand, the green just sits on the surface as a dry, unmelted layer. For this type of work, stains need to be mixed into a glaze-like recipe of compatible chemistry (a medium) to create a good, paintable color. The blue is powerful, it would only need to comprise 5-10% of the recipe total. Its medium would need to have a stiffer melt (so the cobalt fluxes it to the desired degree of melt fluidity). A higher percentage of the green stain is needed, perhaps double. It's medium needs much more melt fluidity since the stain is refractory. Of course, only repeated testing would get them just right. Guidelines of the stain manufacturer for chemistry compatibility need to be consulted also (as certain stains will not develop their color unless their glaze medium host has a compatible chemistry). And, to be as paintable as possible, use use a gum-solution/water mix (e.g. 2 parts water to one part gum solution).

Related Pictures

Why it is not a good idea to use straight stain

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 (having 20% kaolin), it lays down better, accepts the overglaze layer better (because it has less glycerine), presents less problems in handling before glazing and it has no issues with the overglaze crawling off during firing. Black stains are potent, a 75:25 stain:glaze mix would work even better.

Links

Articles	An Overview of Ceramic Stains Understanding the advantages of disadvantages of stains vs. oxide colors is the key to choosing the best approach
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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