The common suggestion is to mix sodium bicarbonate baking soda with CA, but this is a chemical reaction and can generate heat and cure quickly. The talcum powder (gypsum based) doesn't produce a chemical reaction - it just adds bulk. You have to mix the CA in well, since the surface tension will keep it from mixing at first. The thickness of the putty can be adjusted by changing the amount of talc or CA. When it hardens, the putty has a similar hardness to styrene.
Tested has a great video on this: https://www.youtube.com/watch?v=NA2XJ7PTT3M
Thanks Frank, much appreciated.
