I used the same oil-based clay as for sculpting. I probably should have used some water-based clay. The oil clay stuck to the model and took a lot of cleanup between mold halves. Thank you for the talcum tip. I will do that next time, as I very often get some edge bubbles. I did have an assistant bumping the sides of the mold as I poured, and tipping the mold back and forth periodically. Due to the odd shape of the model, I feared for a few potential bubble spots.
I'm about ready to de-mold the casting. I will see if the bumping worked.
~ Vonnor