GardenOfImagination demonstrates how to make clay molds. To make clay molds with rubber stamps you can use your scrap clay. First, you need to condition your clay by working it in your hands. This will make it easy to work with and get all of the wrinkles in it. Then roll it into a ball and flatten it out just a tiny bit to get it ready for the rubber stamp. Next, pick out the rubber stamp you wish to use for your mold. Make sure that the clay is spread out to the size that you need. Then take the stamp and push it into the clay. To make sure that you get a good imprint press firmly and slightly rock the stamp back and forth and side to side. Make sure that you do not pick up the stamp until you are sure you are done. Then carefully scrape it up from the surface and cook it. This will make your mold. You can also use other things to make a mold. She used a dome shaped button to make a bowl mold. She did this by rolling the spare clay into a ball. Then flatten it slightly between the flat part of your hands (not too much). Then squish the button in the clay and pull it out. If it is a metal button or object you can cook it in the mold so it doesn't lose any detail. You can also just pull it out and cook it.
When your mold is all done you are free to use it. For a flat mold all you have to do is take a piece of clay and push it into the mold and then pull it out. You should have a detailed shape. Then use a knife to cut the shape out. If you have a mold that is not flat like a bowl shape. She recommends that you put some cornstarch in the mold and then dump it out and blow on the bowl (you can also use mineral oil or clay conditioning oil). This will make it easier to remove the clay from the mold. Another alternative is to put the clay in the mold scoop out any excess and then put it in the fridge (30min) or freezer (15min). Then take it out and the clay will be stiff enough to remove from the mold and bake.