Making small molds for plaster casting part 1

Awhile back I took Stephanie Lee's plaster workshop online. I've been experimenting with making smallish
molds to use in my work so I thought I'd share what I've learned about 3 mold making materials that don't cost as much as materials dedicated to molding.

Part one will be making the actual mold-what I learned about the materials I tried. Part two will be using the molds to make small, low relief items.

The first material I used was silicon caulk. I used Elmer's Squeez'n Caulk (clear) because I already had it. I'm sure you can find cheaper silicon caulk in larger sizes for less per oz.

                                           
If the object you're using to make the mold (I'll call this the matrix from now on) is metal or painted it will be affected by the silicon (turn green, paint will come off).

If the matrix has a hole in it sew it down to freezer paper. This keeps it stable while you're applying the caulk. Use freezer paper under the silicon mold. It'll be easier to remove when it's dry.

I'd suggest using the clear silicon caulk. It goes down milky white but becomes transparent as it dries, letting you know when it's time to remove the mold. Apply the caulk in several layers, letting each layer dry before applying the next one.

Your mold will be flexible after it dries, making it easier to remove the molded object. This material takes the longest to dry/cure but the flexibility is a big plus for me.

The second mold making material I tried was Das air hardening clay.

I did some online study before using this and one person said it can be baked in a 300 degree oven if it's too thick to air dry. The drying time is several days in a sunny inside location. Mine have been drying for 3 days and still are very cool, a sign that the inside is still damp. For an air dry clay, this takes wonderful detail. I didn't find the reported shrinkage (up to 3% reported by some users) to be a problem. With small molds this could be a problem. It took deep relief with no distortion. The mold is rigid when dry.

It comes out of the package ready to use with no real conditioning. In fact, it's better not to fold it as fold lines are hard to smooth out. I learned online to put it in a ziplock and keep it in the fridge. Completely non
toxic so that's ok.

The next mold making material I used was Sculpy. I have arthritis in two fingers so splurged on 'mold making' sculpy softener along with the large white block so I wouldn't have to condition (knead) it so much.

I cut a piece of each in this proportion; 1/4 conditioner, 3/4 sculpy. ONLY use this for making molds. It's too squishy to use in molds and will get stuck permanently in small areas.

The toxicity of sculpy hasn't been cleared up in my mind. When I bake it I have the toaster oven in front of the window with a fan blowing all fumes out of the house or, better still, put the toaster oven outside when baking it. Also, pick up a used toaster oven at the thrift store and only use it for sculpy-not for food.

Adding the softener made it very easy to condition. It took the matrix with deep relief. There was slight distortion of the mold as I removed it. This material has little shrinkage but must be cooked/cured completely.
So with my 3/8" thick molds I cooked it in two sessions at 275 degrees for 20 minutes each. I think this won't be such a good mold for plaster as the silicon but we'll see. Next, I'll try each mold and share what I've learned.

Here's a great website for polymer clay.