NOT the George Costanza kind, the RTV silicone kind. I was feeling pretty chuffed to have made my own mold of the Hirst starship walls and was cranking them out at an impressive rate. Now I see that my mold shrank quite a bit, and they're about 1/16" too short.
That's a decrease of 1/32" per inch, about .0312 inches per linear inch. In the picture, you can see a casting placed over a master and flush on the left side. I used Alumilite Quick-Set RTV silicone, picked up at Hobby Lobby at a half-price sale. I talked to Carol in their customer support, and it's apparently rated for .6% linear shrinkage, or .006 in./in. (all of this assuming my math is correct). I don't know what went wrong, but I'm hoping Alumilite can give some tips to prevent it.
In the meantime, I placed an order for a quart of Smooth-On OOMOO 30 RTV Silicone, which is rated for .0025 in./in. I need to make another mold anyway...I think I'm going to do 1/2" walls around halls and rooms built on 1" square boundries. That means I need to make some 1/2" wide pieces at the same rate as the walls, so I will need at the very least another mold of them, or more than likely, a new, hopefully more accurate mold, incorporating both.
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