I made a disappointing discovery when I went to use my molds- they've become brittle and are starting to crack! I've had them for about a year or less. I never have had this problem before. At first I thought it was because they were old, but the ones I made in the late spring are the same way as my older ones. I'm wondering if it is the heat and maybe the humidity...? I had been using Sculpty Mold Maker. I plan to switch to a silicone mold material instead and hopefully it will work out better.
I think that they could be created by tinting clear silicone caulking with oil paint then using a piping bag and frosting tips. I'm not sure how it will look when you mix the paint. I imagine that if you use a small amount it will just tint it and if you use more it'll be cloudy/less transparent. This theory is based on tinting white silicone, it should be somewhat the same. I'm going to give it a try and will post the results.