Funny, I'm really enjoying these posts on polymer clay, sharing 'all my knowledge' (with tongue firmly planted in cheek saying that), and doing research to find more info. But it seems that every time I hit post, I start thinking of more stuff. Either second guessing myself that I completely left something out, or usually, just more, more, more! stuff I can add.
On that note:
A little more on making your own push molds.
Making a mold from more poly clay, is very easy, and you don't have to purchase anything extra, but it won't be nearly as flexible as the silicone kind. You will definitely need to put some sort of talc or powder in the mold because the clay will want to stick to itself. The firm clays hold the shape well, but you could even leave the object you are making the mold from in the clay when you bake the poly clay mold IF it will withstand the oven temperature.
Using the silicone two-part medium to make a mold will make your mold much more flexible, but there is a tricky time frame involved. You mix the two substances together, and within a few minutes (I think it depends on the brand, but about 10) it will start to harden, so you have to be on top of things when you get ready to mix.
Either way you do it, you can make a mold from anything, ANYTHING. Buttons, pendants, silverware patterns, leaves, toys, stuff from gum ball machines, game pieces, sticks, other crafts, cloth, anything you find laying around.
Again, if you make a mold from something that was originally designed by someone else, there is the tricky matter of can you sell it as your own.