Glad you sorted it out.
If you're casting in latex, then a stone or plaster mold is ideal. The porosity allows you to dwell the latex to build up a thickness. Use a non-porous mold, and you'll have to build up thin layers a little at a time, which is always kind of a bummer.
If you're doing silicone, keep in mind you'll want to stick with tin silicone so as not to have the presence of latex inhibit a platinum. You could still cast that in a stone mold, or pretty much anything else, provided you release the master accordingly. The downside of gypsum is that it degrades faster than other materials, so if you were to need a bunch of castings in silicone, you might go for something more durable, but expense often comes into play, too, so it really comes down to your needs and preferences.
