Book - Chapter 4 - Alginate Molds

Clasping Hands Life Casting by Melissa Hildreth

Melissa had to do a speech on a technical process. After some thought she decided to do it on life casting. Below are the steps she used to create her casting. The model is of her and my hands clasped together.

STEP 1: Deciding what to cast.

Before making a life casting several things need to be thought through. For example, what will you be casting? How are you going to pull the master from the alginate mold? Do you need some form of a mold release? How much work time do you have with the algnate? Will it require a couple of trial runs to insert the master? What kind of casting medium are you going to use? These and other question will arise while you are in the process of deciding what to make your mold of. In this case we are going to make a mold of two hands clasped together. This instance requires a little forethought on how do you get the model out without destroying the soft alginate mold material. What we discovered was that Melissa would have to gently uncurl her fingers from aound mine while slipping her wrist and hand free of the alginate. We practiced this a few times as well to get the feel of the technique.

STEP 2: Prepping the model.

The next thing we did was to examine the model. My hand has lots of hair on it, so to prevent it sticking to the alginate it is given a thin coat of vaseline to slick the hair down. Alginate does not harden to the point that it wil pull the hair out, but there would be no way of replicating the hair with plaster.

STEP 3: Mixing the alginate.

Alginate comes in a powdered form and is available at Walmart and other craft stores. It is not generally sold as alginate but rather in a kit form to make molds of baby's hands or feet, or as a kit to make a plaque of your childs hand like you get from your first grader from school. Buying alginate like this can be cost prohibitive. These little 3 and 4 ounce packages are expensive and it takes a lot of them to do a big project. You can order alginate in larger quatities from suppliers located on the internet, or if you are in good with your dentist, through them. The volume of water required to mix the alginate comes with the product. In this photo you see we used a whisk to mix it. DON'T DO THAT!!! The whisk mixed in an enormous amount of air that left a billion little air holes in the finished mold. If you get air trapped in the mold the end casting may have little nodules sticking off of it. These nodules are easy to clean off with a sharp exacto knife or similar implement. I would suggest mixing the alginate with a spoon and doing so by gently stiring it to help reduce the amount of trapped air. It is worth noting that I don't think it is possible to mix the stuff without getting a little air trapped in it. Mixing time varies by the temperature of the water. Generally speaking, colder water allows more time for the alginate to set up. Warmer water will cause it it set faster. But regardless of the water temperature you have a very limited amount of time to complete the project. I mixed with cold water and I had a work time of about 6 minutes, with warm water it would have been even less. By work time I mean from the time you have it mixed until is has fully set.

STEP 4: Inserting the model into the alginate.

After the alginate is mixed it is time to insert the model. There are a few things to keep in mind when you make a mold of things. 1) You should study the model very carefully. Any undercuts will create a lock in the mold that will prevent you from pulling the model out without breaking the mold. This is particularly true with inanimate objects. 2) When molding something living and moveable like your hand, you have a little more room to work. Think ahead of time what position your model will be in and how can you extract it from the mold without breaking the mold material. Alginate, when it has set up is firm and cool to touch. It is quite moist and will flex a little bit. Melissa tells me that it has the firmness of cream cheese so you have a good idea of what you are playing with. Keep your model in the alginate until it sets. When alginate sets, it will turn from a pink color to white. You can see in the photo above that the material has a light pink tinge of color to it, and you can see from this photo that it has turned white. As I mentioned above, the time it takes to set up is only minutes so you have to work quick and have the details worked out before you mix it up.

STEP 5: Pulling the model from the alginate mold.

When the alginate has fully set you will need to pull the model from the mold. In our case our hands were clasped together and we had to think ahead of time how to get them out without damaging the mold. After some experimentation, we discovered that if Melissa would uncurl her fingers from mine as she pulled her hand free that she could get it out without breaking the mold. After she pulled her hand free I was able to pull mine from the mold. At this point you can breathe a sigh of relief. Good or bad you're done with the mold, and there is nothing more you can do except fill it with some sort of casting medium.

STEP 6: Selecting the casting medium.

There are a lot of materials made that you can cast with. Some are good for one type of application and others are better suited for others. The selection of what you cast with really largely depends on what the mold is made from. Alginate contains a lot of water and the skin is very moist. So what ever medium you choose make sure that water will not react with it. For this application I have selected a gypsum based product called Die Stone. Die Stone is manufactured by Kerr Labs and is used in the dental industry to cast molds made from people's teeth and gums. Dentists use these casts to help them make crowns for their patients. Die Stone, being a gypsum product works very much like its cousin Plaster of Paris. It mixes the same way. The difference however is the strength of the two products. Die Stone is very hard and durable and will resist breakage much better than plaster of paris.

STEP 7: Casting the alginate mold.

There are a number of different methods to mixing gypsum products and different people swear by their method. I like my method as well as the next person likes theirs. I won't swear by it though. It is just how I like to mix it up. I start with some amount of water in a container. I slowly add the dry powder to the water to allow it to soak it up and to reduce the amount of air that I trap into it. I continue to add the powder until I get little islands formed on the top of the surface. When the water can take no more powder I let it sit a minute or so to really soak through. Looking at the picture above you can see the islands of Die Stone on the surface of the water. After giving the powder a chance to soak up the water I gently mix it with a spatula. When the Die Stone has been mixed it is poured into the Alginate mold gently to help prevent trapping any unwanted air. Here you see me pouring the die stone into the mold. When the mold is full, the sides are rapped sharply to bring any trapped air to the surface. Then it is allowed to sit until the Die Stone has fully set up. I let large molds set overnight, although it is ready within a couple of hours of being poured to be removed from the mold.

STEP 8: Demolding the casting.

Once the Die Stone or whatever you are using to cast the mold has fully cured you can demold the casting from it. Alginate is soft and easy to tear. To demold this casting Melissa simply tore the mold away from the finished piece. It is possible to get a few casts from a single mold as long as a few conditions are met. First, the master you are molding must be a simple object with no undercut or it will tear the alginate mold when you try to pull it from it. A work around is to take a sharp knife and cut the mold in such a way as to allow you to take the casting from the mold without tearing it up. When you do this you can slide the mold back into its container and cast another one. The life of alginate is very short. As water evaporates from it, it will shrink. You can get some interesting effects like this as well. Alginate is soft so it needs support when you fill it with your casting medium. If you don't the mold can sag and your finished cast will look different from your original model. Below are several views of the finished casting. Melissa intends on doing a bronze finish on this casting and mounting it on a piece of wood stained cherry and putting it on display in the living room. When it is finished I will put pictures of it here for you to see.

Life casting can open up a whole new world of adventure. You can create casts that are so life like that they are hard to believe. You can cast anything you like with alginate. Try your hand, your foot, your face, you spouse's torso, or anything else you like. Alginate is completely safe to use on any part of your body or any perishable item, like fresh fruit, plants and other items. In the future, I want to try a life cast of a face and when I do, I will put it here for all to see. I hope you have enjoyed this example. Be sure to tell your friends about it and come back occasionally to see what has happened on MY HEAP!