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Make a two part reusable mold using plaster
Quote "2) Press in an object well greased" You are suggesting placing the object directly into the wet plaster? This has issues depending on the object being cast. The most obvious issue is the object may just sink into the plaster and be impossible to remove without breaking and therefore ruining the mold. The play-doh is there to help control the mold line.
Hi, I'm going to ale a mold for a bronze casting and am torn about the medium to use. I am casting a finale, a pyramidal shape with a height of about 6 inches, as well as a base width of about 6 inches. I was originally going to cast it using sand, but this method seems far easier, all things considered. Do you think that this plaster method will work with that volume? I think I'll need to make it a three part mold to accommodate the void in it.
I am not sure why you need playdough. Can't you just make the first half mold using plaster? I guess not but I am not sure why. Also, as joemellin says, the need for a "spill guard" is unclear. Why not just use a tupperware (as you did) and keep the bottom intact, grease oil or soap it and prize the first half out of the still intact tupperware container? The way I had envisioned is1) fill a tupperware half full with plaster2) Press in an object well greased. 3) (Thanks to you) Add some straws for pouring and some small objects around the half submerged object for the "lego-like" fit. 4) Wait till solid. Grease/oil/soap again and pour on another half of plaster. I am not sure of the need for the playdough.
I really like your method of creating a seal around each half of the model with play doh. It's so much easier and quicker than trying to cut the shape of the model into a base board and sealing the gaps around the edges after. For small models like that shell though, I would suggest using mold putty to create a mold. It's significantly quicker and easier than using plaster which has a tendency to break when de-molding, espiecally from objects with fine detail like that shell. Plus wax is delicate to begin with so fine detail won't survive a rigid mold being ripped off.Also worth noting with wax is that it will crack with sudden temperature changes. In other words, don't put it in the freezer to dry quicker or it will fall apart when you take it out.
Thanks for the info. I am planning on doing my first pewter pour of a small art object. I have two questions. Is there a special kind of plaster I should use when pouring pewter? and also. Can I pour into a plaster multi-piece mold? Thanks. Gary O
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