Casting With Silicone
Advantages of Silicone:
It's as useful as latex, but sets a lot more quickly. It can take days to build enough layers of latex to create a mold, but some silicones can be mixed, poured and set within a matter of hours, even minutes depending on what kind of silicone you use. Silicone is generally a lot stronger than latex and will produce more castings on average.
Disadvantages of Silicone:
It's a lot more expensive than latex. The pint I used in my experiments cost me 28.50 including shipping. (And I got it on ebay which is one of the more cheaper places to find it. See my Links Page for a list of online stores which offer silicone for sale.) Another disadvantage: it is made from two chemicals which must be mixed in a 10:1 ratio, meaning you WILL need a scale to measure and mix the silicone.
Don't bother buying an expensive digital scale for mixing silicone - a small plastic food scale will do. I bought mine from Target for 5.99. You can see it in the picture below. (That and the small box I made to place the object that I want to cast. I made the box out of pieces of foamcore (aka foamboard) that I hotglued together.)
Take a small plastic cup and place it on the scale. Pour in as much of the "cake batter-y" part of the silicone that you'll think you'll need. Record the weight (in this case, 200 grams.) Set that cup aside. Next, put another plastic cup onto the scale and pour in the dark-colored catalyst. (It's purple in this case, but it can be blue or some other color, depending on what kind of silicone it is.) Since you used 200 grams of the first substance, you'll need to measure out 20 grams of the catalyst.
Combine the two substances and mix with a plastic utensil. (Do it over a sink. The silicone won't stick to anything but itself, but still, it's not good to slop it anywhere where it might make a mess or be in other people's way.)
Next step: Pouring the Mold...