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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.
Blend the two types, permanent and washable, with a powdered colorant, 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 be a ceramic stain mix with a melter medium (a glaze or frit).
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).
Glossary |
Stain Medium
It is a mistake to use pure stains for decorating ware. Stains need to be mixed with a ceramic carrier and a working medium to work and fire well. |
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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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