The blue is melting and bleeding profusely into the glaze. The green is the opposite - refractory, stiffening the glaze enough to trap bubbles and sit on the surface as a dry, unmelted layer. 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 considered safe for direct food contact. Stains are expensive. Stains don't suspend in water, paint poorly and dry as a loose powder.
Both of these (and others) need to be added, as a minor percentage, to a ceramic carrier (one with CMC gum and a mix of ceramic materials tailored to melt to the desired degree and have a compatible chemistry to develop the color (as per manufacturer guidelines).

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One well known artist blends these the two types, permanent and washable, with a powdered ceramic pigment, in the proportions appropriate to get as much hardness as possible but not so much that it is difficult to clean up the screen. The powder should not be a pure ceramic stain, it should bee mixed with a melter medium so it fires to an adequate degree and similar thermal expansion as the body.

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The logo on the left was rubber-stamped using an ink mix made of Mason 6666 black stain in a glycerine carrier. During firing, the glaze is shedding off. The stain is refractory yet still bleeding excessively into the overlying glaze. Further, it does not melt during firing, so it does not glass-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 stamps better, inherits better lay down, accepts the overglaze better, and dries harder.

This picture has its own page with more detail, click here to see it.
This flaking is happening at the interface between the body and orange commercial underglaze (the firing is cone 05). The reason is simple.
Pure stains contribute only one ceramic property: Color! Commercial underglazes sold in jars dilute stains into a recipe of materials, a powder medium, designed to impart the missing properties. However, suppliers like to quote products as suitable over a wide range (e.g. cone 06-6). Of course, at cone 06, they have almost no glass development for bonding to the body and at cone 6 they may well be melted. In this case, the stain used is refractory and a high percentage is needed. So the bond with the body is very poor. A thick layer coupled with an incompatible thermal expansion can make the underglaze/glaze layer pop right off.
Is a DIY version possible? Imagine if you created a powder medium (e.g. L3685Z3) containing enough frit to counter the refractory character of the stain and develop the needed glass to bond with the body. That would solve this problem.
| 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. Or can be sintered into super materials. |
| Glossary |
Stain Medium
A stain medium (or ceramic medium) is a mix of powdered ceramic materials that impart ceramic properties that stain powders lack in themselves (e.g. ability to form a hard ceramic that fits the underlying body or overlying glaze. |
| Glossary |
Ceramic Stain
Ceramic stains are engineered crystalline pigment powders. They are used as an alternative to employing metal oxide 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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