Tips for Safe Plaster Casting and Molds

Working with plaster is a messy business. You should expect to get dirty, and need to plan out the process with all of your tools on hand for a smooth operation. When working, it is best to try to keep anything you may need within arm's length for easy accessibility. Here are some lessons from experience when plaster casting:

Use lots of Vaseline! Particularly when casting flesh, do NOT skimp on the Vaseline. It is there to act as a barrier between the plaster and your skin. As the plaster dries, it gets very warm, sometimes hot, and can easily burn your skin and pull off hairs if they are not slicked down. Vaseline will protect you from such occurrences. Along with this, it is best to have lotion on hand for when you are finished. Multiple castings of the same skin can cause burns and dryness over a period of time. Keep your skin hydrated.

When casting your own hand, practice setting up so that you can reach everything with the other hand. Also keep a large pile of loose towels nearby, so if you need a clean hand, you can quickly rub off. My setup is like this: Cup of warm water, empty bowl for mixing plaster, multiple disposable spoons, towels, Vaseline, plastic sheeting (under everything), Bluette (for casting after molding), visible clock, bag of plaster, Plastilina (oil-based clay), paintbrush (not your good ones!)hammer and flathead screwdriver.

When casting, it is very helpful to consider the structure of the cast around the piece. Be wary of sections that may be too complicated that can break when removing the cast. Sometimes, it is easier to build a mold in multiple parts to avoid this. This is also important when casting thin, delicate areas and objects. which may break if either a. The plaster is not dry/not strong enough/not mixed well, or b. The piece could not withstand the actual breaking open of the mold, and snapped at the blow.

If your piece breaks cleanly after opening the mold, you have a few options if you do not want to re-cast the piece. If it is small enough that the bond will hold, score on both sides of the break in opposite directions, like a checkerboard. Mix a small cup of plaster; keep it slightly thin, but not watery. Put a clean layer of this new plaster on both sides of the break, and hold together until dry.

If your piece breaks at a larger area and you need a stronger hold, it needs to be reinforced from the inside. This same method is also used to affix two separate casts together into one piece. First, drill or carve a hole into each side of the reinforced areas. Make sure you have on hand a sturdy piece of metal; piping, heavy duty wire, etc, depending on your needs. Check that the piece fitting on the inside matches with your holes cleanly. Now, follow the same directions as above and score the two sides and mix a new batch of plaster. Fill the holes and cover both sides with plaster, place the reinforcement inside, and hold firm until dry. Let seepage occur; this will assist in hiding the seam. When complete, you will most likely have to sand this down. If the seam or break is still showing, you can review this step and add extra plaster, dry, and sand down again until it no longer shows.

The Plastilina mentioned above is crucial when creating molds with multiple sections. The oil-based clay is inexpensive, reusable, and will not stick to the plaster. For the first piece of the mold, form the Plastilina in the shape of the desired piece on the object. This will keep the plaster in place while drying, and can be removed after the plaster is dry.

The Bluette is used specifically when casting a plaster piece from a plaster mold. Any food coloring should work, I prefer Bluette as it is sold in large bottles, and is relatively inexpensive. A lot goes a long way. After completing your mold, mix some plaster very thinly, and add some Bluette to give it a tint. Use a paintbrush to paint around the edges of the mold, and let dry. Afterwards, place a layer of Vaseline over the Bluette inside the mold which will allow the casting to separate once dry. Proceed with casting, and when your cast has dried, you will be clearly able to see the blue line at the seam, which will make it much easier to remove the piece from the mold without breaking either. Place the flathead directly on the line, and tap with the hammer gently.

And last but not least, listen to your intuition. If the plaster is getting to hot for your skin, take it off. If you do not think you put on enough Vaseline, do the steps over. Wash and moisturize your hands on a regular basis, even if you are casting an inanimate object. Plaster casting can affect your skin slowly over time, so make sure you take care of yourself and your work. Like so many have said before; Check twice, do once!