Reading a topic in Hip Pocket and following the links got me thinking about using silicone for molds with cornstarch for a quick curing agent. Then I saw the article in ModelGeek using latex. The method I made up is quicker and simpler.
I ran across some 1/72 PM Model kits of secret German jets that never made it past the drafting board. I was thinking it would be cool to build a Me P-1111 or a Lippish P.13a. The kits are very basic, and I decided they would be fun to add a few details to. My imagination acted up, and I ended up getting a 1/72 Me 262 B-1a 2 seat night fighter for more parts. When the German Revell kit was opened it was so nice I couldn't bring myself to chopping it up. That's when I remembered silicone molds. Looking through my caulking collection, the only silicone was type II, no cornstarch either. The parts were so small I figured curing time wouldn't be a problem.
First, I made a mold of an instrument panel. I cut up a toothpick and put a few pieces over the first layer of silicone to stiffen it a bit. Then put some more silicone over that. The mold was made while the part was still on the sprue. I tried not to get too much on the back of the part. Since I wasn't in a hurry, I let the mold cure overnight. Note: 2 hours wasn’t long enough to cure a Silicone II mold ¼ inch thick.
The next day the mold with the plastic part was cut from the sprue. The plastic part was left in while trimming excess silicone off the flat back of the part. It turned out to be difficult to trim the silicone. The silicone was so flexible and tough it was hard to shave a clean edge. Maybe put the mold in the freezer to stiffen for trimming? Maybe the Silicone cornstarch mix is a little stiffer? In the end the flexibility was a plus. After mixing a drop of 5 minute epoxy and mushing it into the mold and letting it set for an hour, the epoxy part popped right out of the mold. Even with the undercuts from the sprue and somewhat ragged back it was easy. The epoxy was set but not cured. Trimming off the flash was easy with a hobby knife.
There was another interesting possibility. The part could be curved and bent. Make masters of somewhat 3/D parts flat, then bend them to shape after they come out of the mold. Timing would be important. Another property of the epoxy is that it settles flat in the open top of the mold. You don’t have to worry too much about the back of the casting being smooth. Finally, it is so easy to make tiny parts like instrument panels that 3 or 4 can be made to try painting techniques on, or a backup in case the original part doesn’t turn out well.
The photo shows an instrument panel mold with epoxy in it and 2 cast panels, one painted dark gray. The middle mold has the original part below it. The mold on the right was taken from the side detail of the inside of the cockpit of the above model. Although the photo doesn’t show, some epoxy was pushed into the grooves with most scraped off the surface. Then the mold was placed in the undetailed cockpit below and clamped with a clothes pin. In an hour the Lippish 13 had raised cockpit panel lines on one side.

Tim,

Nice write up, but, um, I don't see any link images.

sorry for my ineptitude. couldn't figure a way to put it with my post. The photo is in my gallery. Wish I could drag and drop!