Thank you!
Yeah, mixing hot is a good tip.
Really looking forward to your friend's answer – advice from someone who tried it is highly appreciated.
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I've ran into this (haven't tried it yet though):
20 lbs. microcrystalline wax
1¼ gal. #10 weight oil
7 lbs. plain automotive grease
50 lbs. gritless dry clay powder (Such as Kentucky ball clay, or Gordon clay)
Melt wax, oil, and grease together in an electric frying kettle; stir clay in slowly once melted. Pour into shallow microwave-safe plastic containers, or into a wet plaster mold.
from “Sculpture Casting,” by Kowal and Meilach, ~1972
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I should convert it to metric, but apart from that:
Microcrystalline wax – i wonder what's that and how much different it is from parafine
Regular "10W-30" should work as 10 weight oil
Plain automotive grease – "solidol" should work
For clay – pretty much any fine clay (non-chamotte) will do.
I'll keep posted if i try anything of this.