Testing Commercial Ceramic Glazes Over Texture in Electric Kilns

testing ceramic glaze-695

To get the most out of commercial ceramic glazes in your electric kiln, you need to understand the product descriptions on the package. What do the manufacturers mean when they say opaque, semi transparent, or translucent, and do their descriptions match the descriptions in your head? Of course, the best way to find this out is to test, test, test!

Deanna Ranlett has done some of that testing legwork for you and in today’s post, an excerpt from our free download Techniques & Tips for Electric Kilns, she shares the results of testing some commercial ceramic glazes over texture in her electric kiln. – Jennifer Harnetty, editor.


Part of navigating the use of commercial glazes is understanding the phraseology on the jar. Most glaze manufacturers use terms such as opaque, semi-translucent, translucent, transparent, etc., on their labels. But what do those words really mean? How would each affect the surface if you like to sgraffito, add thick slip, use sprigs, carve, or stamp? To answer this question, I designed a test tile with a little of each of these techniques to test cone 04 and cone 6 commercial glazes and to illustrate some important factors to consider when using these glazes.

The test tiles included: sgraffito using Amaco’s LUG-1 Black Underglaze; dots of white slip made with Little Loafers and 5% Zircopax; an incised diagonal pattern; gemstone-shaped sprigs from plaster molds; a row of stamps; and finally a water-etching. It’s important to make a test bar of your desired texture techniques to use when trying out new glazes so you don’t expect one thing from reading the label or looking at a small tile and get a result you aren’t happy with.

I followed the manufacturer’s directions and brushed three coats of glaze on each tile with a soft fan brush, then glaze fired the tiles to cone 04 or cone 6.


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Opaque Ceramic Glazes

Opaque means not letting light through: not transparent.

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Tile #1 Mayco Olive Green FN-021, fired to cone 04: The glaze creates a thick layer of color, almost as if the tile has been coated in paint or dipped into colored rubber. The glaze flows into the incised lines and stamps, and there are only breaks in the glaze where the texture is deep. Even the black underglaze is obscured. This glaze would be ideal if you needed very solid coverage.

Tile #3 Mayco Copper Float SW-129, fired to cone 6: The glaze creates a thick layer of color and added sparkle with copper-like flecks. It has a very interactive surface while being opaque—meaning that all opaque glazes are not alike. This glaze shows a lot more of the texture and highlights the deeper lines while interacting with the black underglaze to create a deep, shimmery black in that area.

Semi-Transparent Ceramic Glazes

Semi-transparent means partially or imperfectly transparent.

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Tile #4 Amaco Robin’s Egg TP-26, fired to cone 04: The glaze is capable of showing a break over deeper stamped and water-etched textures, shows a slight break on the gemstone sprigs, and gives highlights on the slip-trailed dots. However, it’s very cloudy over the black underglaze—not showing much of the black, so it wouldn’t be a good choice for sgraffito work.

Tile #6 Mayco Green Opal SW-253, fired to cone 6: This glaze creates pools of frothy spring green and, while the glaze fills in some of the texture and incised lines, it acts to highlight breaks over texture and slip trailing and also shows the black underglaze very well in the sgraffitoed areas.

Translucent/Transparent Ceramic Glazes

Translucent means clear or allowing light to pass through. This type of glaze is perfect for highlighting fine details.

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Tile #8 Mayco Sky Diamonds CG-975, fired to cone 04: The glaze is showing off each texture to its full advantage, you can see the black underglaze very well and you can also see every facet of the gemstone sprig. It’s worth noting that the physical larger crystal granules you see when applying this glaze pop and pool during firing and you can lose details in those areas. The crystals are the blue and white dots scattered across the fired surface of the tile. You can control this effect to some extent by placing the crystals where you want them when you’re brushing on the glaze.

Tile #10 Mayco Turquoise SW-201, fired to cone 6: This glaze highlights the textures on the tile, isn’t quite as transparent as the Amaco celadon, but still a lovely glaze to use over a variety of textures. The black underglaze is particularly pretty with the turquoise over it.

Deanna Ranlett owns Atlanta Clay in Atlanta, Georgia (http://www.atlclayworks.org/) and MudFire in Decatur, Georgia (www.mudfire.com).

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