There's a thread on a cake forum about making food safe molds from homemade ingredients...It drove me crazy when it first started because there was so much debate on it about what recipe would work. The thing is, that kind of stuff has been used for decades (if not longer) to make molds and prosthetics. I know, because we used to use gelatin to make molds way back in the dark ages when I was in high school theater. You don't need to experiment with recipes, they already exist and they're easy to use.
I did a quick search and found this tutorial on instructables.com. It goes over how to use gelatin, glycerine, honey and water to make molds and prosthetics. Take a look and tell me that this isn't simple: Gelatin Molds
There was a company that used to make a similar kind of thing that I purchased from years ago. It looks like this:
The benefit of this kind of thing is that it's made from ingredients that are readily available at the grocery store. You can also melt the molds and re-use the material again, so as long as you keep it clean you only need to make it once.
However...There's a definite downside to it, which is why we theater people all got super excited when they started developing skin-safe mold materials and we didn't have to use this gelatin garbage anymore.
First, it's just kind of gross. It smells nasty when you're working with it, and it has a creepy texture to it.
If you can get over that (and it's not such a big deal, but I don't like gelatin in general) you have to keep in mind that this stuff is re-meltable, Which means that it will melt. It can be used for cold applications like fondant and gumpaste, but you can't use it for isomalt or things like resins that will heat up when it's curing. It will melt the detail right off of the cast mold, which is fairly counterproductive.
Last, it's a pourable medium, so you run more of a risk of getting air bubbles and other imperfections in the molds than you would with a putty silicone. It takes some practice to learn how to make an error-free mold. (Then there's the issue of having to have the actual item in the actual correct size to mold, but that's another story.)
It's also not cheap to make. Yes, you can re-use it, but it takes a decent amount of gelatin to make a large-ish piece, and that isn't cheap. I'm always kind of surprised when I see how much gelatin costs. And it takes a fair amount of glycerine, too.
If you're going to make your own molds, I'd recommend using the two-part putty that you can get at the craft store, and use a discount coupon to get it. The silicone molds are more permanent and you can use them with isomalt without worrying about melting them. But knowing how to make the gelatin ones is handy, so bookmark the instructables site and write that recipe down!
Actually, here it is:
1 part honey
1 part water
2 parts gelatin (not the sheet kind)
2 parts glycerine
Using small cups or a measuring cup (start small, maybe 1/4 to 1/2 cup) fill it with gelatin crystals.
Take the same size measuring cup and fill it half full with warm water. Pour the honey in to fill the cup, then put it in a pyrex measuring cup or a microwaveable bowl.
Fill the same size measuring cup with glycerine and pour it into the pyrex cup.
Put the pyrex cup into the microwave and heat it for about 15-20 seconds to dissolve the liquids. Stir well. The liquid should be warm but not boiling hot for the next step. (If you boil gelatin you can destroy it's ability to gel correctly)
Add the gelatin to the pyrex cup and put it in the microwave for about 15-20 seconds. Stir to dissolve the crystals. If they don't dissolve completely put it back in the microwave for ten-second increments to heat, stirring after each heating. DO NOT let the gelatin boil!!!!!
Put the whole thing in the fridge for at least 4-5 hours, until it cools down completely and solidifies. At this point you can take it out of the cup by prying it out, and you'll be able to store it in a plastic bag in the fridge until you need it. To use, reheat it using short bursts in the microwave, then pour it around or over the item to be molded. Make sure it cools down COMPLETELY before removing the item from it.
Kara Buntin owns A Cake To Remember LLC, online cake supplies at www.acaketoremember.com and www.acaketoremember.etsy.com