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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).

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Details

A glaze used on lower sections of ceramic and pottery that catches (and stops) runny glazes. Reactive glazes are almost always runny, the interesting surfaces they produce are a consequence of their high melt fluidity. Common functional glazes can be very glossy yet not run at all, they can thus act as a catch to arrest the flow of others. When the color and surface are chosen well their presence can go unnoticed (even on the insides of ware). In many cases, a catch glaze can also act as a liner glaze that not only makes pieces more food-safe but also stops the formation of a lake of thick runny glaze from creating a glaze compression problem.

Related Information

Stop a runny glaze with another glaze!

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Two iron red mugs

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.

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

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Tenmoku stoneware mugs

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

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As runny glaze as its own catcher

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.

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Ancient copper running stopped
Cone 6 iron red with a catcher glaze

By Tony Hansen
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