Making terra sigillata

[BHClaysmith]

Terra Sigillata enhanced stoneware vase fired to cone 6 in an electric kiln.

BASIC MIXING INSTRUCTIONS

BASIC SIG
200 grams White ball clay such as Tenn 10 or Kyom4
800 grams water (3 ½ Cups)
10 grams Calgone*

Use hot water and add the Calgone* to dissolve. Add the clay, stir thoroughly and allow to ‘sit’ undisturbed for 2 – 7 days in a tall clear glass or clear plastic jar (A large mouth opening is preferable). The mixture will divide into 3 distinct layers. Use a siphon and go down through the top layer of water to the bottom of the middle layer (which is the Terra Sigillata) and siphon it into a clean container. I then keep some of the top layer of water to add to my sig later in case it gets too thick. Dispose of the bottom clay layer in a responsible manner.
If the sig still seems a little thin (it should be the consistency of light cream) allow it to sit uncovered for a week or two and remove some of the top water before stirring to mix to obtain the proper consistency. Add colorants after decanting and ball mill if possible to retard settling.
“AGED” Terra Sigillata is some of the best! – some artists allow all the water to evaporate from the sig and then store it in powder form, adding water back into it as needed.

*CALGONE is sodium hexametaphosphate.