Lichens and Lizards and Leopards, Oh My! Reticulated Glaze Recipes For Wild Ceramic Surfaces


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Although glaze crawling – when glaze recedes away from an area in the firing, leaving bare clay – is often considered to be a glaze defect that should be avoided, many ceramic artists use this so-called defect quite effectively as an intentional decorative element. Glazes are sometimes formulated to intentionally crawl and create reticulated surfaces resembling lichens, leopard coats, or lizard skin.

Here, Robin Hopper presents a slip recipe and a base glaze recipe for such an effect, and gives examples of this slip and glaze combination with various ceramic colorants added. – Jennifer Poellot Harnetty, Editor.


Glaze Crawling, On Purpose

A group of specialized glazes have come into favor in the last 15 years: glazes that show patterns of heavy crawling, or reticulation, with patterns that look similar to lichens, lizard skin, and leopard skin depending on the glaze base, underglaze coatings, and temperature of firing. The same glaze may give very different results at a variety of temperatures.

Putting the reticulation glazes over a colored slip allows the top glaze to move and the visible cracks to be colored between “islands” of glaze. Any colored slip will do, but one of the most interesting is usually black.

Black Slip Recipe Glaze Material

Ball Clay          35%

Barnard Clay   45

Feldspar           10

Silica                 10

Total               100%

With the following reticulation glazes applied heavily over the slip and fired at cones 04, 6, and 10, and with added colorants, a wide range of textural possibilities can be developed (see images below). The main requirement in the glaze is a heavy saturation of magnesium carbonate.

Base Glaze Recipe
Glaze Material Percentage
Soda Feldspar 29.0%
Magnesium Carbonate 30.0
Ferro Frit 3134 9.6
Ferro Frit 3195 5.7
Talc 7.6
Kaolin 18.1
Total 100.0%

Add: Zinc Oxide5.7%

Note: This glaze should not be used on surfaces that come into contact with food.

You will note in the photographs below that the overglaze fuses greatly at the higher temperature (Cone 9), giving smooth surfaces, whereas, at the lower temperatures (Cone 6), the glaze will be either beaded or dry and crispy like dried mud. Similar results can often be achieved by putting many matt glazes over glazes that are much more fluid. The more fluid glaze will generally start to melt earlier during the firing, encouraging fissures to develop in the matt glaze surface. So-called leopard skin glazes are usually done this way. The reticulation glaze may be colored with any colorants and stains.


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This tile features the above base glaze and slip with a 5% addition of Blythe Yellow Stain 14 H 236. Fired in oxidation to Cone 6


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This tile features the above base glaze and slip with a 5% addition of Chromium Oxide. Fired in oxidation to Cone 6.


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This tile features the above base glaze and slip with a 4% addition of Cobalt Carbonate. Fired in reduction to Cone 9.

Most of these glazes have been applied over a simple black slip in order to intensify the color of the covering glaze. Any black slip would be suitable to use. The one used here is from the formula above. Other colored background slips greatly extend the possibilities of palette. Firing these glazes at a wide variety of temperatures from cone 04 to cone 10 also greatly extends the possibilities.


**First published in September 2013
Comments
  • Hi! The recipe does not indicate if the slip is put on the raw clay and then biscuited before glazing or applied to the biscuited pot and the glaze applied on top of the slip. Can anyone clear up this point? Thanks, Ken

  • Usually, I would put a thicker than avg coat of black slip, bisque fire, then crawl glaze and re-fire. The evaporation of the high elemental water content in magnesium is what causes it to separate when the kiln heats up. Tip: Dip with tongs, wipe off bottom, and pack directly onto kiln shelf. You don’t want to touch the glaze with anything once it has been dipped. It tends to show prints, defects, ect easily. One other idea: I sprayed or dipped another glaze, then dipped in the crawl, I got some real neat crawl/slide results!

  • Thanks Stephanie, A very full answer and it is good to know why an effect takes place as well as how to achieve it. Ken

  • Subscriber T.

    Hi!
    This is really great. We don’t get Barnard Clay so is there a substitute for it?

    Thanks
    Seema

  • Melinda C.

    If it is on the underside of a low bowl, for example, any trouble with spitting, or falling onto the kiln shelf?

  • karen E.

    Hi this glaze looks really exciting cant wait to try it. Ive been looking for a substitute for barnard clay as we dont have any in NZ. I use a white slip over Feenys BRT raku clay made of china clay (kaolin) and ball clay and fritt 3134. Im not sure if this slip will be ok if I add some copper oxide or black stain to it and use that any suggestions
    would be super helpful 🙂

  • azadeh d.

    hi, I use ready glaze, a kind of pbo frits, I tried to make this texture but I could not, maelp may you help me for combination?also may help for reduction, I made one kind of cu reduction , dard ana mat red, and also made tourqusie from cu and co , and slips but I can not make good extenshin for this glaze?

  • susan r.

    Hi!i agree….Im guessing that slip is essential for the crawling glaze to work? Is this correct? I’m guessing that the slip is put on and then biscuited pot and the crawling glaze applied on top of the slip. Is this right?

  • It works just as well over bisqued terra sigillata. I make it from OM4 or Newman’s Red. Add any colourants you like.

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