terra sig

[Iforgot]

Hey world,

 

Does anyone have a good Terra sig recipie that is mesured in grams?

 

 

 

Thanks!

Darrel

[bciskepottery]

from Sumi von Dassow

 

White terra sigillata

 

2.1 kg (2 litres/3.7 pints) water

 

1 kg (2.2 lb) OM4 ball clay

 

25 g Darvan 7 or Darvan 811

 

 

Red terra sigillata

 

2.2 kg (2.2 litres/3.9 pints) water

 

1 kg (2.2 lb) Newman Red Clay

 

30 g Darvan 7 or Darvan 811

 

 

· Measure water into large glass or clear plastic jar with a wide mouth.

 

· Add Darvan and stir.

 

· Add clay and shake vigorously. Leave undisturbed for three hours

 

· After three hours, you will see a layer of sludge at the bottom of the container. Siphon off the liquid portion above the layer of sludge. Be careful you don’t pick up any of the sludge. After siphoning, discard the bottom layer of sludge.

 

· Try the terra sigillata on a dry test tile. If it doesn’t give an adequate shine or still feels gritty when you rub it with your fingers, let the terra sigillata sit for another 12 to 24 hours. Siphon again and discard the new sludge. One sign that you have a bad batch of terra sigillata is if it soaks in and dries quickly.

 

· If there are dark specks in the terra sigillata, put it through a 200-mesh sieve. Even if there are not dark specks, it won’t hurt to screen it anyway. It should be about the right consistency to use right away (a specific gravity of 1.15) but if you want it thicker, let it evaporate for a day or two.

 

· Apply two or three coats to bone-dry ware, allow to dry just until the surface isn’t wet, and burnish with fingers, a soft cloth (cotton tee shirt), nylon stocking, chamois-leather, car-polishing mitt, a plastic bag (dry cleaning bag). Don’t touch the wet surface (wear latex or nitrile gloves) and make sure your polishing cloth is very clean. For the greatest shine, apply three thin coats, polishing between coats.

 

· For colors, add oxides or stains after settling. If you add too much, the terra sigillata won’t burnish as well because these materials have a larger particle size than terra sigillata (ball milling the oxides and stains can make the particles finer).

 

 

Then, again, using a pound to gram converter on the internet, any recipe can be easily recalculated.

 

 

[yedrow]

Can you substitute sodium silicate for the Darvan, and if so, at what ratio?

 

Joel.

[Chris Campbell]

Copying this from Vince Pitelka's online recipe ....

 

Preparing the Deflocculant

 

The secret of refining a proper terra sigillata is to settle out all but the very finest particles. A deflocculant is a chemical additive that causes particles in aqueous suspension to repel one another, and it is a critical part of the terra sig process. Only a tiny amount of deflocculant is needed, and adding additional is counterproductive, so be very careful with your math and your measuring. Soda ash (sodium carbonate) and sodium silicate both work as deflocculants, but for reasons that no one seems to understand, a combination of the two work best in terra sig.

 

The amount of deflocculant is figured as a percentage of the dry weight of clay to be used. To a small amount of hot water, add 0.25% (1/4 of 1%) soda ash (sodium carbonate) and 0.25% sodium silicate. A hand blender will make short work of dissolving the chemicals. The sodium silicate comes as a liquid, but just measure the weight as if it were a solid.

[yedrow]

Thank you Chris!