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My sister had a baby. She sent me the baby's footprint pressed into plaster. I would like to use a silica mold material I got from C&R Loo and fill the footprint to be used as a mold. I'm wondering if the silica mold will release from the plaster casting or do I need some type of separator?

Hell yes you need a separator!
When making a plaster to plaster(type) mold, I separate the two parts with a layer of vaseline that has been thinned w/ mineral spirits (I think). The thinner evaporates and leaves a nice thin layer of grease. Two layers just in case I missed a spot on the first layer.
You might want to practice once on something not so precious until you feel like you've got it because if you mess up, Plaster tends to stick to plaster and then both parts are destroyed if you try to separate them...

If you are new to working with plaster, it is very much worth your time and money to go to a ceramics supply store and get a simple book on making plaster molds and read it. It will save you many times its cost in time, frustration, clean up, materials and real money. Just looking at the pictures will help a lot.

Think of how many ways you can go wrong with a material that turns from a liquid into a rock. You can turn your clothes into rocks, your drain pipes into rocks, your tools, your skin, your lawn, ....

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Will take both of your advice. Fortunately, I had my sister send me a couple of samples, so I can afford to lose one.

Thanks again,
Mira

I use Murphy Oil Soap (as the separator) which can be found at any large supermarket. It has worked for me....and the price is right. Let me know if you try it.

PAM, yes Pam, and actually the generics work as well. The advantage is that with vaseline straight, you will pick up the smear marks.