Published May 1, 2019
Ceramic artist Joan Carcia delights in the fact that she never quite knows how each of her saggar-fired vessels will turn out. She can influence the results, but there is always an element of surprise in the outcome. That is the most exciting part, she says.
This week, we will take a look at how Carcia uses terra sigillata, vegetation, oxides and salts to make her vividly colored work. - Jennifer Poellot Harnetty, editor
I handbuild my saggars using coils or slabs. I find the best saggars are about 2 inches wider and 2-3 inches deeper than the piece being fired. This allows for 1 inch of packing material around the piece and 1-1 1/2 inches at the bottom and top. Often, I will put one pot within another, letting the larger pot act as a saggar for the smaller pot. For large saggars I make the wall about 1/2 inch thick. Smaller saggars can have a thinner wall. Saggars built from raku clay last longer, and saggars built in the same shape as the piece enhance the outcome.
The materials I use when packing saggars are green hay, salt-marsh hay, sawdust, seaweed, straw, salt, and sometimes flower stems and petals. I mix the salt-marsh hay and sawdust with copper carbonate, cobalt carbonate, yellow ochre and iron oxide. I put a bed of materials on the bottom of the saggar and place small crucibles (made of clay) containing salt around the bottom. Then I either place the pot in and gently put other materials around the side of the pot, or wrap and tie materials in place around the pot using copper wire, reed or even string and then place it into the saggar. Materials are then placed on top and the saggar is covered.
I fire the saggars in a gas kiln, raising the temperature slowly as the materials burn. The fumes produced during the firing get absorbed into the porous pot, and the results are the colorful visual designs and tactile markings on the pots. It should take about 6 1/2 hours to get to the desired temperature of Cone 012, firing in oxidation. Reduction takes place within the saggars as combustible materials use the available oxygen.
This recipe (see ingredients below) makes about 1 cup of white terra sigillata. Mix it in a 1-gallon container with a lid. Mix the trisodium phosphate into the water, then add the clay slowly over a period of 15-20 minutes, letting each addition slake down before adding more. After all the clay has been added, let it sit for about half an hour, then vigorously mix with a spatula for about two minutes. Then put the lid on the jar and shake it vigorously for another two or three minutes. Next, place it in a spot where it will not get moved for two weeks.
After two weeks, siphon off the clear water on top. Then, using a turkey baster, siphon the next layer (terra sigillata) and put it into a jar for using. Throw out the sediment that is left at the bottom. The terra sigillata should be like skim milk in consistency. If it is too thick, you can add a little water.
I apply this terra sigillata to bone-dry pots with a soft brush, overlapping my strokes. I put two or three coats on and burnish the pot either after each coat or after the final coat with a soft cloth. It is important to stir the terra sigillata mixture to keep it in suspension during application. I bisque my pots to Cone 08 before firing in the gas kiln.
More images of Joan Carcia's work can be seen at www.jcarcia.com.
**First published in 2008.