Question:
How do I make a plaster mold
Mixing plaster
You will need potting plaster for molds,(it is stronger and finer), for a bucket of plaster you will need to fill the bucket to just under 2/3 water, then, wearing a mask, as plaster is toxic, consistantly shake in handfuls/containerfuls of plaster evenly over the water the plaster will fall and settle. When the plaster is forming islands, ie, lumps of grey surrounded by water), shake the plaster onto the water until all is absorbed and the top of the bucket is covered in plaster. Wait until all plaster has gone grey (there should by this time be no water), then stir with your hand, fingers slightly splayed, and move your wrist from side to side, in order to mix the plaster, (this eliminates air bubbles). When all the plaster has been dissolved it is ready to pour. Tap the bucket all around. If you have some air bubbles on top of the mix, either scum off with a paper towel or spray with a mix of water and metho 10%. Once the plaster is disolved, time is a crucial factor. You must get the bucket poured and rinsed within minutes. For this reason organisation is imperative.
The Plaster, once poured will heat, then it will cool, once cool it is ready to take from the mold.
Making Plaster Molds
Making a Simple Plaster Mold
Plaster molds are used in ceramics to pour multiples of a single object with liquid clay (slip). Making a mold can be a daunting task, depending on its complexity.
Due to the length of this tip, it is placed in the Articles section of this site 'Making a simple plaster mold'
Or go to:
http://www.ceramics-tips.com/RscArticleV.asp?id=375
Adding plaster(start)
Using a cup or scoop, start adding plaster to the water. Sprinkle the plaster out evenly over the whole surface of the water. You don't have to be in a big hurry, but don't work too slowly or the plaster will start to set. Some people prefer to sift the plaster into the water. At first the plaster will sit on the surface of the water very briefly before it disappears beneath the surface of the water. (This is called "slaking".)
Slab flop mould
Slab flop mould:
Anything can be used as a mould, although plaster is preferred, any object can be used.
Roll slab as in introduction, leave it to firm approx 1/2 hour.
Gently insert slab into mould and press against walls, trim excess, and leave till leather hard. Remove from mould and allow to dry. The piece is now ready for bisquing!
Smoothing your mold
Smooth the top of your plaster item with a rib or something like that, and let it set. Clean your bucket and tools at this time.
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