Now, why would I want to cast starfish when I can buy real starfish for as little as a buck a piece (or even less)? Well, the fact that these pretty animals are harvested alive for decor purposes just makes me cringe, therefor I don't buy starfish (nor shells or any other sea life). If you feel the same, you'll love this project!
What you'll need is Urethane Mold Rubber (comes in two parts) and Mold Release Spray. I ordered everything from ill Street Composites.
Then you'll need a flat frame or box. Husb made up this simple wood frame. I have three finger starfish that I received as a gift (see Sparkling Glitter Crafts). One of the starfish was a perfect model! Flat and nicely shaped. Oh, and if you can figure out how to make a frame that's starfish shaped, do so! Turned out the square rubber mold was a bit stiff which made it hard to release the cast starfish, so I ended up cutting away lots of material. Why waste rubber mold if you don't have to, right.
Apply plenty of silicon sealer around all the starfish fingers so the rubber urethane mold will not undercut. Try to align with the outermost edge of the starfish, then it will be easy to release the cast starfish. I wish I had done a better job with this!! And as seen in the previous picture, coat everything with mold release spray. Be very generous!
Then, mix the two parts of rubber urethane mold together and pour until starfish is covered. Let dry over night.
Release time! Disassemble your frame.
Update: Becca's question (see comment):
How much did the supplies cost to make the mold?
Mold material $24 and release spray $9. If you plan to cast many starfish, it's well worth it! And the plaster is really inexpensive -coming up next week!