After a few minutes, they would wriggle their hands free, and the operator of the booth would pour a plaster compound into the mold, and have the customer return in 30 minutes for the finished piece.
My coworker didn't pay to have his hand cast, but instead did a little research online, and for Christmas obtained all the materials and did casts for all his nieces and nephews.
Since that time I've wanted to do it for my children, but for various reasons never did so. I decided I would try this out for mother's day - if I make four molds, one for each child, then make three castings from each mold I would have enough for a complete set of four for their mother and each grandmother.
This is a Mother's day present I can really sink my hands into!
Step 1: Requirements and Preparation
AlginateThis molding compound forms a rubbery elastomer within minutes of mixing with water. Captures impressive detail, while being flexible enough to prevent entrapment of the hand. It dries and shrinks over time, so it's not suitable for more than a few castings. I used ALG-390 from Special Effect Supply Corporation, which is a 3 minute set alginate.
Casting PlasterMany plasters are available for casting, you can even use the inexpensive local plaster you find in any hardware store. I used a particular formula called Hydrostone which features high strength, and high detail. This also came from FX Supply, as item HYD, and is a 20 minute set plaster.
Mold containersI used 1/2 gallon jugs, 1/2 gallon juice bottles, and 2 liter pop bottles. The only difference was that when I needed to cut away the mold, the plastic juice bottle and 2 liter bottles were a little harder to cut.
Hot waterA cold mold is uncomfortable, so start with hot water. By the time you get it mixed it should be at a comfortably warm temperature.
Machine screws and nutsIf you don't want to break the mold, you have to have something sticking out of the casting once it's hardened in order to pull it out. Can also be used to mount the finished piece onto another project.
Small pieces of cardboardUsed to hold the screws in place while the casting cures.
MixerI used a cordless drill and one egg beater. A regular mixer should work, and for large batches a jiffy mixer (paint mixing drill attachment) is recommended. Don't plan on mixing this by hand as there isn't enough time. Also note that the plaster is abrasive and may damage the beater.
ScaleThese materials settle and compress so they should be mixed by weight. However, the working range of the mixture is pretty good, and in a crunch I believe suitable result can be obtained from volume measurements which will be detailed below. I'm using a postal scale that can measure in tenths of ounces up to 10 pounds, which is the range needed for small hand molds and casts.
Containers & cupsYou'll want to stage your materials, measuring both the water and powder into separate containers, and then mix them together. Therefore you'll need containers suitable for holding the pre-measured materials. The cups are useful for scooping powder out of the supply buckets.
Watch or TimerYou'll need to time the molding process fairly carefully to obtain good results, so keep a timer handy. When you're elbow deep in any project it can be hard to accurately judge time.
Box knifeUsed to cut the molding container top off, and later cut the container away from the mold when you want to break the mold.
Long sharp knifeI found it necessary to cut and level the top of the mold so the cardboard holding the screws was level. A knife long enough to cut all the way through prevents tearing the mold.
ScissorsUsed to cut the top off the molding container, and is more convenient than the box cutter for some containers once the cut is started.
Pocket multi-toolUsed for a variety of tasks, depending on your skill and the tool it may replace several of the other tools.
Plastic forks, paper towelsNot necessary, but you may want them on hand for various tasks, such as scraping hardened molding and casting materials off various surfaces, cleaning spills, etc.
Please note that while the materials are not generally toxic (check with your supplier), you should not use any of these tools for food later.
Tool/Material layoutYou'll need a full table for your first time. It can be done in a smaller space, but room to work is helpful as you may be worried about time during the molding stage, and looking for a spot to set the water pitcher is a distraction.
A chair for the person whose hand is being molded is nice. People tend to shift their weight frequently when standing, which can cause a mold to be damaged while setting.
A utility sink is useful for later cleanup.
Assistants: This can be done alone, though in my case I had four eager assistants helping me by taking pictures, holding containers during mixing, and providing opportunities to practice my collision avoidance and balance during the process.