you make the mix yourself.. 50% pottery plaster and 50% silica flour..you can get it from a pottery supply store.. . mix the 2 together dry, then add water.. Its always best to mix up more wet plaster than you need than less when your ready to pour..
If I was to cast up a Tin that had had patterns on 2 sides, I would make up a prototype out of plasticene(sp?) (plastic clay) it would look like a tin on a lollypop also find a gromet you like for the nose and tail and place them in the clay this will make space in the final mold to place a grommet.. the lollypop handle would be the gateway to pour the molten tin into. I would then take the proto and make a 2part silicone mold of the proto. Then I would make 3 or 4 rubber models of the proto... Now from here, I would make a square form out of wood or something and i would suspend the rubber tins in the middle of the box.(spray the tins with cooking spray or silicone spray as a mold release, ) now i would mix up some plaster/silica mix and pour in the plaster until the level came up halfway on the sides of the tins.. Let that harden up till it gets slightly hard and then with a spoon or something make some half round holes in corners of the plaster... after a few hours it should be rock hard.. now take some of that cooking spray or vasaline and coat the layer of plaster and pour in some more plaster- when its hard, carefully take the plaster out of the form, and split them apart carefully. then remove the rubber tin protos- now you have a tin mold- if you wanted to go comando, you could substitute the plaster for casting wax and make a wax mold- then send it of to a foundery and have a mold made out of bronze- it would cost a couple hundred $$ but your great great great grandkids could use it
for a butterfish mold, you could get away with a one piece mold... this would be really easy compared to the 2 piece method, make a plastic clay butterfish- flat on oneside and a keel shape on the other make sure there are no undercuts(dont forget the gromit)- lay it on a flat surface, keel side up and build a little box around it. pour some straight plaster around it and let it harden up.. when hard, scrape out the clay carefully, and make 3 or 4 rubber prototypes.. Then take your 4 protos and lay the flat sides on a flat surface.. make a box around those- now pour in your 50/50 plaster silica mix- this will be your final mold. lift it up and pull out the rubber protos-
Now for casting tin into the plaster molds, you'll want to coat the cavities with a light coating of talcum powder and you might have to do 2 or 3 pourings to heat up the plaster enough to get a good one- and for heavens sake, be patient and let your plaster molds dry out for a few weeks in a dry place so there is zero moisture in them.. hot tin and lead dont like moisture.. you could even dry the mold out in your oven at 200 degrees for a few hours for safe measure -
i hope someone does this and sends me some tins
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