Saggar firing was originally developed to protect wares from ash-slagging and flame-flashing in wood firings, but in contemporary use, with clean-burning gas firings, the process is used in exactly the opposite way: to contain fumes around a pot so that the pot to picks up color from the fumes. Saggars are the lidded containers used to contain and isolate pots during a saggar firing. Most often, saggars are made from coarse sculpture clays that can withstand repeated heating and cooling. But some potters make aluminum foil saggars that do the trick quite nicely.
Today, in an excerpt from her book Low Firing and Burnishing, Sumi Von Dassow explains how potter Edgeworth Barnes fires his pottery in aluminum foil saggars with great results. - Jennifer Harnetty, editor.
Edgeworth Barnes uses one part each of copper sulfate, fine sea salt, cottonseed meal, baking soda, and 1/2 part each copper carbonate and titanium dioxide in his saggars. For larger pots he mixes these materials with water to create an evil-looking bubbling liquid he calls "swamp juice" and brushes this juice directly onto the saggar to avoid having all the chemicals concentrated only near the bottom of the pot. He also uses coarse steel wool, copper wire and seaweed. For saggars for larger pots he suggests using two shallow bowls for the top and bottom of the saggar, and adjusting the height of the saggar by placing rings of thrown clay between the bowls. He punches holes in the rims of his saggars to allow airflow, and fires to 1600 degrees F (870 degrees C) in about an hour.
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Inexpensive is emphasized, as ferric chloride is caustic and toxic. It will ruin good brushes, eat away at metal parts on a spray gun, and corrode your metal banding wheel if it comes into contact with it. If you choose to spray ferric chloride, you must wear gloves, goggles and a face mask and spray in a well-ventilated area. Despite all these serious disclaimers, ferric chloride is fairly commonly used because it reliably yields spectacular pink to orange colors.
After all the pots are coated with the ferric chloride, Barnes mixes up the same swamp juice in a shallow bowl with just enough water to make the mixture froth. Once this has bubbled up and increased in volume he touches the pot to the bubbling mass. This leaves a lacy deposit on the surface where it contacts the pot. The swamp juice can also be brushed or splashed onto the pot. The saggar is made with foil that has been crinkled up and then spread back out. He scatters a little coarse steel wool, raw cotton and wood chips on the foil. Next he places moistened seaweed over these materials. Copper wire or pieces of copper dish scrubber can also be added to the mix. Next the pot is placed, usually top down, onto all these items.
More seaweed, cotton, wood chips and steel wool are then placed over the pot. Finally, the foil is wrapped around to cover the pot and pressed into close contact. The operative words here are "a little" of each of these materials -- too much combustible material can result in solid black pots if the foil doesn't burn away.
The pots are tumble-stacked in a kiln and fired to 1260 degrees F (680 degrees C - about cone 017), at which point much of the foil will have vaporized. It is important to do this outside away from people and homes! Ferric chloride and the other materials will create very toxic smoke as they burn.