How to Make a Stone Casting - Head/Shoulders
If you want a sturdy lifecast, then a stone material is a good choice. It's strong enough to take quite a bit of abuse, it's heavy enough to stand on it's own without needing to be fastened to your work table, and yet if you make it hollow, it won't be too heavy to move around or store. Ultracal or Hydrocal are good stone choices. I don't recommend plaster because it is far too soft.
For this tutorial, I am going to use the plaster bandage mold that was created in the head/shoulders lifecasting tutorial.
First you start with a mold. Make sure that the two halves of the mold have been fastened tightly together. I use plaster bandages, making sure to seal all of the seams. Allow the plaster time to set and harden, so it won't come loose. The seams must be stong, or they may come apart or leak when you fill the mold.
Place the mold upside down in a 5-gallon bucket or a sturdy crate. Place some old towels or other material in the bucket to cushion the top of the head, and to keep the mold centered in the bucket. It is also a good idea to cover the floor area where you are going to work with a plastic painter's tarp, since spills and splatters are an inevitable part of working with stone products.
Coat the inside of the mold with a release agent. This step is very important! If you do not coat every area inside the mold, the stone will stick to your plaster and you won't be able to seperate the two. Make sure to coat inside every nook and cranny, and use a bit of release to fill the hairline cracks of the seam lines to help reduce their size. Vaseline is cheap and readily available, but it also makes your job slightly more difficult because the liqid stone mix will run right off of it like water off an oil slick. A high quality mold wax or mold release are somewhat easier to work with in the long run, but will still cause you a bit of trouble. It's just something we have to deal with. If you aren't sure if a release agent will work well, do a small test to find out. Better to spend some time doing a test than to fill your mold and discover that you can't remove the mold from the casting afterwards!
Cut up some burlap. I use strips, usually 2 inch by 5 inch, or 4 inch squares. You will need a pretty big stack, so be sure to cut plenty. Anything you don't use now can be used for the next project, so don't worry about cutting too much.
Mix enough Utracal (or Hydrocal, etc) to almost fill the head area of your mold. I use a flexible 1-gallon plastic bucket (the kind that budget ice cream comes in). I fill it with 2 or 3 inches of warm water, and then slowly sift the Ultracal into the bucket. DO NOT STIR the powder into the water! Let it keep soaking up the water and sinking to the bottom. Eventually the water will become saturated with the powder, and then the powder will begin staying on the water surface. Reduce the amount of powder that you are sifting into the bucket, but keep slowly sifting in powder until a 'dry lake bed' effect begins to form on the top. At that point, let it sit for a few more minutes. If a wet area forms around the outer edges of the bucket, sift a bit more powder to soak up the water.
Wait several minutes, and then stir the Ultracal mix. Use your hand (preferably with gloves on to keep it from drying out your skin), and break up any clumps you find with your fingers.
Pour the Ultracal mixture into the head of the mold. The warm water will help it to set up faster. What you need to do now is use your hand to scoop ultracal out of the head area and spread it across the neck and shoulder areas of the mold. It will be difficult at first, because the Ultracal will run right off the release slickened plaster. But as the Ultracal begins to set up, it will get thicker and will begin sticking to the side walls of the mold.
Continue scooping Ultracal out of the bottom of the mold and spreading it until there is an even layer of Ultracal over the entire inside surface of the mold. Try to avoid trapping air pockets as you work. This is the inside of your mold, so it doesn't have to be pretty. Just make sure to give it as even a coating as you can.
After the first coat of Ultracal has begun to set up, mix a second batch. Use cold water this time to give yourself more working time before it begins to set. This time, you will dip pieces of burlap into the mix and then spread them across the inside of the mold, very much like the way you dipped and applied the plaster bandages earlier. The burlap will make the lifecast stronger, and will help hold the Ultracal together if it ever gets cracked. I try to cover the entire inside of the casting with 3 or 4 pieces of Ultracal-soaked burlap. I put extra layers in the neck and around the base, where all of the stone's weight will be resting.
Place a plastic bag over the casting and leave it there for a couple hours. As the Ultracal cures, it will begin to heat up... which in turn evaporates the water. Much like concrete, the final casting will be stronger if you retain the moisture level for a while.
Remove the plastic bag and allow the Ultracal to set for a few more hours. It can be removed from the bucket now, but it's better to play things safe and just let it sit. The longer you let it rest, the stronger the casting will be. I often let Ultracal molds sit overnight before I put any stress on them. Better safe than sorry!
Take the casting and mold out of the bucket, and cut the seal that is holding the two halves of the mold together. Then, if you coated the inside well, the plaster bandage mold can be pulled off in large pieces. If you missed putting release on any spots it will stick in those places, and you'll have to pull hard to get the mold off.
Clean off any bits of plaster bandage, wipe away any release that was left on the Ultracal, and use a plaster file to scrape away any seam lines... and you should have an exact replica of the person you made the lifecast of!
Before you begin sculpting on your lifecast, it is a good idea to use a plaster rasp or file to smooth the bottom edge of the casting so that it will have a flat bottom. You don't want it to rock or tip while you're working on a sculpture! Professionals often use a bit of Ultracal to give their lifecasts a perfectly smooth base, not only to make it look very finished, but also to avoid any rough places that might scratch them when they're carrying the cast around their studios.