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).
Stain Ceramic stains are manufactured powders. They are used as an alternative to employing metal oxide powders and have many advantages.
Overglaze A method of applying decoration over the glaze surface of ceramics. It can be done before or after the glaze firing.
Glaze Layering In hobby ceramics and pottery it is common to layer glazes for visual effects. Using brush-on glazes it is easy. But how to do it with dipping glazes? Or apply brush-ons on to dipped base coats?
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.
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.