silicon mold Q?

[rosanna gusler]

i made some silicon molds of shells and starfish with silicone caulk. i have been using bo-shield (a waxy lubricant that i had laying around) to lube them before pouring with plaster/alumina. this is working ok but do i really need to do this step? rosanna

[Jenna]

I spray my silicone patterns with some rubbing alcohol right before I pour (evaporates quickly). The 'wetness' helps the plaster flow across the silicone and not trap any bubbles as you pour. the alcohol lowers the surface tension of the water in your investment helping to break any small bubbles suspended in the plaster from mixing. You can also give a light spritz to the top (mold base) of the plaster and you'll find that this will flatten out the base of the mold making much easier to level during firing.
This is a fairly recent discovery for me but all the molds(60+) that I've fired seem to be completely unaffected by the alcohol. (so far)
Hope this helps.