I see ads in FSM for a mold-making material called ComposiMold, that sounds pretty neat. Has anyone tried this stuff?
I was curious about it too, so I did some searching on the YouTubes. I found this guy, and he has a lot of trouble with bubbles.
I wonder if the bubbles are from the mold material itself or the design of the mold. I had to work a lot with mold design before I got rid of bubbles in the castings, but I think I have learned now how to do it properly. Were the bubbles he had trouble with in the mold itself, or in the castings made from the mold?
If you watch the last five minutes of the video, he opens the mold and sees all the bubbles. The mold is too poor to even bother making a casting.
It looks to me like the Composimold is just too viscous to work on an intricate master.
Not so good! The interesting thing about silicone is that while it looks viscous when you pour it, it certainly nestles down well in the details! Only problems with silicone are cost and somewhat limited shelf life. 'Course, one of the ads for the Composimold said “no shelf life.” I figured that was just an odd way of saying it. To me long shelf life is good, no shelf life means it goes bad as soon as you open the container 
That IS an odd way of describing it. Soulds like it’s bad before you buy it. 
I was really hopeful when I first learned about Composimold, thought it could save a lot of money.