| Yes, Murphys can be used. If you a doing
a lot of moldmaking, I would suggest a jar of "plastilube" (from Aardvark Clay)
or a similar soap. It doesn't have the detergents that Murphy's does, it's just formulated
to seal the plaster. You can also use motor oil, I understand, but haven't tried this. I
have used Murphy's in a pinch and I would suggest thinning it maybe with 1/3 water, that
seems to help encourage the Murphy's to lay better on the plaster, otherwise it's kind of
goopy.
When soaping, you must be VERY DRY with your soaping sponge or brush. If you use a very wet sponge, or allow the soap to lay in the deep crevasses, the soap will seal some of the plaster under the sculpture. You can be sure that the plaster is well soaped when it looks somewhat shiny and water droplets don't absorb into it. Just drop a few drops of water from your fingertips on the sealed plaster, and the same onto some unsealed plaster, for comparison. Then you will always know what the sealed plaster looks and acts like. Three coats, wiped off in between with a damp sponge, will assure you of a good surface. And make sure not to scratch the surface, or really handle it, after soaping or you'd better soap again. Undersoaping will cause the mold to stick together and you will have plaster that stays stuck to the other side. Oversoaping will cause the soap to creep under the sculpture, or the rubber master, and there will be shiny edges and shiny surfaces within the negative of the mold, and since the plaster is sealed it will not absorb water from the slip. You can very gently scrape away the seal, it is only on the surface. Better not to oversoap, though. Good luck! Joanie
Editor's note: Here's another short post on the fine art of mold soaping, it just seemed right to put it here. MHCeramists Molds are only soaped when they are first made, to keep the plaster pieces from sticking to each other. Never use anything on the inside of the molds, except for clean water if you must wash away some clay. Even then, only use a slightly damp cloth or sponge. So assemble your clean molds, band them
tightly, make sure your slip is not too thick or too thin. Pour into the hole with a
consistent Keep topping the hole up, until it begins to form a "skin" or wall of thicker slip around the sides. When that skin is the thickness you want it to be, invert the mold and pour the still liquid slip away. Sometimes you have to get up into there with a tool, and remove some of the hardened slip, so that the rest flows out. See previous post for more detailed instructions, and good luck! Joanie |
