Stop a runny glaze with another glaze!

This iron red cone 6 glaze, G3948A (similar to Amaco Ancient Copper), is applied thickly and runs during firing. With no countermeasures, it ends up on the kiln shelf (like the one on the left). Since this glaze breaks-to-black where thin on the edges of contours, glazing the base black seems like a natural match. The base of this was first dipped in G3914A black, up to about 1 cm (1/2 in). I then waxed over all of the black up to within 1-2mm of its edge. Then I applied the iron red by dipping in the normal way for liner glazing mugs. For this thickness of the brown the black melt is able to catch and stop it within 5mm or less.

Related Pictures

Iron red on porcelain and a red burning stoneware

This is the G3948A recipe fired to cone 6 using our standard C6DHSC schedule. The color "breaks" to black where thinner around contours so it seemed like a natural that the inside glaze should be G3914A Alberta Slip black. The contour of the foot ring is important or the glaze will run onto the kiln shelf. My standard fluted ring foot is working well. Perhaps a better option would be to glaze the bottom inch or so with the black as a catch glaze.

High melt fluidity is required to achieve the visual effect of this glaze

This is G3948A, an iron red cone 6 reactive glaze (similar to several commercially available products). The reason for the variegated surface is the high fluidity of the melt. Adequate thickness is also important, enabling it to run downward to some extent. That means this is not actually over-fired. Using it thus requires consideration of the running behavior, accommodating it in the shape of the ware on which it is used. Obviously, using this on the insides of pieces would result in pooling at the base, which would likely produce glaze compression, cracking the piece during cooling. Use on the outsides may require a catch glaze.

A way to prevent a tenmoku glaze from running onto your kiln shelves

Tenmoku reduction fired glazes can be so beautiful yet few people use them. One reason is the melt fluidity - runs stick pieces to the kiln shelf. While the melt fluidity is the key to the appearance it is also the curse. These glazes also pool on inside bottoms producing glaze compression issues. And they stretch thin over rims roughening them with any grit from the body or glaze materials. The running onto the shelf issue at least does have a simple solution: The GR10-A base as a catcher glaze on the outside bottoms and a liner on the inside (and even optionally wrapping over the rim). I use a dipping glaze version of it for the insides and a brushing glaze version for the bases (and up the side walls about 1cm). The tenmokus GR10-K1 (left) and GA10-B (right) can be applied thickly and it’s no problem, 5-10 mm of catcher glaze is all it takes to stop the running.

Use the same runny glaze as its own catch glaze

This is G3948A, a super runny cone 6 iron red glaze. The clay body is M340. This glaze has to be runny, applied thickly enough, be held at temperature and cooled slowly to achieve this visual effect. When applied at the needed thickness it will run off the ware onto the kiln shelf during firing. Why has that not happened? A catcher glaze on the lower section. In this case, the catcher is the same glaze. On the left, the bottom half of the mug has just been dipped into the glaze quickly, giving a layer that is too thin to achieve the red effect. That dried within a few seconds and enabled pushing the top half down into the dipping glaze for twice as long (the inside has a liner glaze and is waxed up to the rim). The upper section glaze is guaranteed to run and the bottom is not thick enough to run. The result is complete blurring of the dividing line and coverage that looks natural and flawless.

Links

Glossary	Catch Glaze A catch glaze of the lower section of a piece of ceramic or pottery is often needed to arrest the flow of reactive runny glazes (so they do not run down on to the kiln shelf).
Glossary	Fluid Melt Glazes Fluid melt glazes and over-melting, over fired, to the point that they run down off ware. This feature enables the development of super-floss and cyrstallization.

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