by Australian Ceramics Clay Stuff

Fifteen years ago I became obsessed with soaking objects in terra sigillata and black firing them. I created The Bears and The Black Books using this technique. The works raised questions about memory, transformation, petrification and mummification, and became a kind of manifesto for things to come.



Clay body                         1.5kg dry material
Frit 4110                           1kg dry material
Terra sigillata                    1.5Lt liquid (see recipe below)
Pine wood shavings         500g pet shop quality

Suggested firing temp: 1050 –1100°C

1. Break clay into small chunks (about the size of a 10 cent coin) and dry out completely.
2. Place dry clay pieces in a container and add the terra sigillata mixture you prepared earlier and leave to slake for at least 12 hours. (see recipe below)
3. Wearing protective clothing, rubber gloves and a safety mask, gently mix wood shavings and frit into the slaked mixture.
4. The mixture should be thick with a consistency like sticky rice.
5. Rest the mixture for another 12 hours so the wood shavings can soak up the frit, clay and terra sigillata. Then mix well.
6. Test small samples of the mixture and fire to recommended temperatures. If the tests seem too brittle, add more frit or try firing to a slightly higher temperature.
7. After testing the mix you’re ready to experiment!


1. Remove all plastic and metal components from your bear.
2. Make an incision in your bear and remove all acrylic stuffing.

3. Now stuff your bear through the incision you made with the prepared clay mixture and stitch up incisions and openings. (My big bears are stuffed solid and can reach thicknesses up to 25cm.)

4. Dry the bears in the kiln by heating the chamber to 100°C. Hold at that temperature until bone dry.
5. Using a syringe fill any air pockets between the fabric and clay ‘stuffing’ and build up the surface by applying layers of the terra sigillata you made previously. (see recipe below)


All firings take place in a gas kiln. Good ventilation is necessary.

Temperature 1050–1100°C

1. The day before firing, preheat bone-dry bears very slowly to 400°C so wood shavings have burned off. This gives better results in the final firing.
2. The final firing is conducted slowly with burners turned to the lowest level possible with the primary air closed nearly all the way.
3. Fire slowly to achieve a top temperature of 1080°C–1100°C over 8 hours.

Temperature 900–950°C

1. Place half a kiln brick at the bottom of a 25 litre metal drum (saggar). Use a drum with a lid and ensure any plastic or rubber seals are removed.
2. Fill the drum with wood shavings up to the level of the brick.
3. Place a fragment of old kiln shelf on the brick to create a shelf space.
4. Tumble stack bone-dry bears. Secure the drum tightly with lid and place in the kiln.
5. Weigh the lid down with a kiln shelf or kiln brick (about 1kg is sufficient).
6. Fire kiln to 900–950°C over five hours.

1. Hardwood shavings create a pewter or graphite like appearance.
2. Pinewood creates a jet black finish on the objects.
3. Experiment by placing different plant materials in the metal tin e.g. bamboo and leaves to create different effects.

All commercial clays, ball clays and found clays can be used to produce terra sigillata. For this recipe, use a transparent 5 litre plastic container with a lid.

1kg dry clay
2.5lt water
25ml sodium silicate

1. Add small pieces of dry clay to the water and leave to slake for 24 hours.
2. Stir well and pass the clay slip mixture through an 80 mesh sieve.
3. Dissolve sodium silicate in 100ml of warm water and add to clay slip.
4. Mix clay slip and sodium silicate well and let mixture rest for another 24 hours.
5. Check that the mixture has separated into different layers. (Sometimes the top layer will be clear water, the layer below this is the terra sigillata. The layers below the terra sigillata may have a slip-like consistency or resemble a sand- or grog-like material. If your mixture has not separated into layers, dissolve 5ml of sodium silicate in 25ml of warm water, mix well and add to the clay slip, then rest the mixture again for 24 hours.)
6. Use a large syringe to gently remove the layer of terra sigillata. (The top of the terra sigillata layer will give the best results. As you move further down the layer, the terra sigillata will be of a lesser quality.)
7. Apply terra sigillata to bone dry objects by dipping, brushing, pouring or spraying.
8. When the terra sigillata is touch dry, buff the surface with your hands, cotton cloth, fine wool, silk, or a fine plastic bag to enhance the sheen.
9. Fire your piece according to the firing temperature or cone of your clay body.

Terra sigillata from stoneware clays can be fired in earthenware, midfire and stoneware temperatures and all atmospheres. My ‘Outback Red’ clay creates beautiful finishes when fired at different temperatures and in different atmospheres, including black-smoke firing and woodfiring. Prepare test tiles and fire them in different temperatures and atmospheres.

Apply layers of terra sigillata on your piece to increase the sheen, or apply a light coat of terra sigillata to bisque ware.

Terracotta clays will only give good results in lower temperatures, while the general rule is that you achieve the highest degree of sheen at lower temperatures. At higher temperatures the level of sheen will decrease. Terra sigillata begins to vitrify at cone 5–6 and will give a satin finish up to cone 10 in reduction and oxidation.

One of the most common problems with terra sigillata is that it tends to peel off during the drying process or after firing. Never let terra sigillata form into pools or droplets as these will shrink and fall off.

Test the fit. The different shrinkage rates between the terra sigillata and clay body is the most common problem when working with terra sigillata. The right application is the only solution to fix this problem. Some clays will allow multiple layers, and some clays will allow only a very light coat of terra sigillata. Testing, testing, and testing is the only safe way to get good results.  

Walter Auer

The Australian Ceramics Association
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