Full Head Casting: Take 1

The largest project in my plan is the full-head casting latex mask. It is done is several parts:  

1. Casting the head into a plaster bust (dry time: one week)

2. Create the clay mock-up

3. Make the second negative mold

4. Make the latex mask using the positive and negative molds

Today I attempted to do the first step: casting a head. Let's just say it did not go as planned. I began by putting a bald cap on my model, cutting the ear holes, and sealing the edges with spirit gum. Unfortunately, it was an ill fitting bald cap so there was some slight puckering that I tried to solve by adding darts. It was not pretty, but they were small defects I could have fixed in the final bust. Then, I completely covered his face, neck, and bald cap in a layer of vaseline to act as a release agent for the alginate. I had the model insert large drinking straws into his nostrils to allow him to continue breathing under the casting.

Next, I began mixing the 3lbs. of alginate. I am using a body-casting grade 8 minute setting alginate. I had pre-measured the powder and water (room temp) in a 1:1 ratio as specified by the manufacturer. I added the water to the powder and mixed until it became a creamy liquid the consistency of cake batter. With a spatula I began applying the alginate in the undercut areas of the face: ears, under the chin, nose, and eyes. By the time I got to the eyes, (2 min) the alginate in my bucket was starting to clump up in a way I have never seen alginate behave before. It looked like a cross between cottage cheese and styrofoam chunks. It became unusable, not sticking to itself or anything else.

I had to abandon my casting attempt because I did not have enough remaining alginate to try again. I am still not sure why the alginate acted in this way and am planning to call the manufacturer tomorrow to discuss what may have happened. I will also do a small test sample with some remaining powder to see if it was user error or possibly a bad batch.

In any case, attempt one has failed. I will try again with a different brand of alginate to see if I can get improved results.

Update: So I have discovered the reason for my alginate fail. My new brand came with more detailed instructions that said to make a test batch because a lot of tap water is not adequate for alginate because it contains too much calcium and phosphorus which will make the alginate clump. Moral of the story: ALWAYS MAKE A TEST BATCH!