Hi, I'm a newby at all this. My grandmother died a couple of years ago and left me 2500 plaster molds and a huge kiln. I almost ruined a small mold by attempting to use plaster of paris. I was able to use a wet cloth to get some off but what was left on top of the mold hardened and wouldnt come off.
I just received my first ceramic slip (1) I poured it into the mold let set for thirty minutes and dumped all the liquid. (2) waited 1 hour when I separated the mold the clay that formed separated also and was still very wet I had to clean the mold again. NO Luck!

I tried again this time I waited overnight before I tried to seperate the mold still no luck the slip stuck to the mold and I had to very carfully rewet and remove all of what I had poured. Any tips on this????

I really like plaster of paris is there any way I can use them with these molds?

Make sure your mold is clean before banding to pour. Open the mold to clear away any dust or debree with a soft brush. Place the mold flat side down and band with rubber mold bands or a mold strap with buckle. To test the mold for pouring, after banding with rubber bands, set the mold hole side up and place fingers in pouiring hole. Try to pull the mold apart with normal pressure. If the mold separates easily, the mold needs more bands or tighter bands. A mold requiring one half gallon or more of slip to fill should be banded with a mold strap.

When the mold is banded properly, fill the mold to the top with liquid clay slip. Do this while moving the slip in a circular or back and forth motion. This will help to prevent hard spots from forming which is where the slip hits the mold at the same spot and starts to set up first. Hard spots have a tendency to keep glaze from applying properly.

After you get the mold filled, it will start to absorb moisture from the slip. As the moisture is drawn from the slip your casting is starting to develope. Check the thickness of the casting with a wooden or plastic mold knife, sometimes called a lucy. Dip the tool into the center of the pouring hole into the slip. Pull the tool against the side of the spare or casting pour hole cutting into the casting. Pull the tool up keeping light pressure against the spare hole. As the tool is taken out the clean part that shows on the tool is the thickness of your casting. A simple method of determining how thick to let the casting setup has been around for ages. It references to nickels and dimes. Most pieces would have a thickness of two nickels placed on top of one another. An object, such as a Christmas tree base, that has to support itself and something else, the tree, needs to be thicker. About four nickels. Thinner items such as ornaments need to be thinner. A dime thickness would be good for this instance.

Once the casting reaches the thickness you desire, pour the excess slip out slowly. If the mold has a small pour hole and a gurgle sounds when dumping the mold, pour it slower so the casting does not pull away from the wall of the mold and collapse. When the mold is completely drained place it up side down (pour hole down) until it completely stops dripping. Turn mold hole side up and let start to dry. When the casting has dried to a damp feel (no longer wet), trim the spare (excess clay) from the pouring hole being careful not to disturb the casting. Unless the top of the casting has a great deal of detail and shape, you can gently loosen the spare from the sides of the mold with the lucy tool. Then, gently pull the spare in towards the center and up, and it will usually break at the end of the spare. You can now take the lucy tool and cut the jagged edges of the spare for a clean casting.


After the casting has had a chance to dry some, remove the bands or strap. Now place your thumbs in the pouring hole and gently separate the mold. When the mold has been separated a little, lift the top half of the mold straight up, and quickly turn the lifted piece over. The inside of the mold is now facing up. Sometimes the casting will remain in the mold half that is lifted. That's why we turn it over quickly. Grab the half of the mold that has the casting. Hold it in one hand and gently hit the mold on the sides using your other hand or rubber mallet until the casting releases from the mold. Once the casting releases, place the mold and casting on table. Using both hands gently grasp the casting and place on clean surface. At this stage your casting is leather ware and is very soft. Be careful not to distort it. Let it set until it is bone dry. The dried piece is greenware.

To clean the casting use a cleaning tool and remove the mold seams from the piece. Be careful not to gouge. Then, if the piece is plain, without detail, wipe down gently with a damp sponge to remove scratches and smooth out. If the greenware is detailed, try not to remove it while cleaning. Using a sponge on a detailed area could very well remove the detail, so we avoid sponging detail. Use the cleaning tool (finger nail) to put the detail back if removed.


http://www.dalzellceramics.com/ceramics/howtopour.htm

Thanks for the tips, I just tried it, works (although I slipped on the floor, on slippery slip, be careful).

Hi, I just stumbled upon your question via a google search. I am currently a student at The School of the Art Institute of Chicago. Plaster of paris is AMAZING, and there are several different ways to work with it, although not as popular as plaster is brittle, and tends to mar with age . If you have one of the 2500 molds your grandmother left you, that you don't care about too terribly; you can pour plaster into it and get a plaster positive, but it may very well destroy any chances of getting accurate images in slipcast porcelain. The easiest way is to use some sort of mold release, liquid dish soap, a commercial mold release, murphy's oil soap, etc. Wipe this mold release WITHIN THE INSIDE OF THE MOLD THOROUGHLY. Mix a little plaster, and pour it in. You should be able to de-mold in a matter of 20 minutes max. To finish, allow Plaster cast to dry until bone hard, and chaulky. Seal with clear coat, or don't. Bone appetite.

Thank you so much for providing these useful tips. I think this will help me some time soon.

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