Molding/Casting a Finger Hook

I chose my left thumb to mold and cast. In mixing alginate and water, I calculated the 4:1 (by weight) alginate to water mixture to be about 1:1 in volume. After the mixture reached a consistency of something similar to thick cake batter, I sank my thumb into the mold. A couple minutes after, the mixture hardened and started peeling away from my thumb.

Pouring in the plaster

For the plaster/water mixture, the consistency was thinner than the alginate/water consistency for me. While the alginate/water was a mustard yellow color, the plaster was a dark gray color. For the first thumb, I just poured it in. For the second thumb, I gently tapped the cup against the table to see if that would help pop any air bubbles.

Imperfections in finger hooks

I carefully cut the mold and excavated the thumbs. Looking at the two thumbs, I notice that they have an incredible level of detail. Every finger line, as well as my fingerprint, can be seen very clearly and distinctly. One imperfection I noticed is how the top of the thumb nail is chipped. I predict that this is because I slightly curved my thumb, so maybe the plaster didn’t reach the tip of the nail. Or, perhaps my thumb was not held completely steady due to accidentally moving or the natural tremor of our hands. I also noticed that there are small bubbles in the crevices of my thumb, like the sides of the nail or the thumb joint. This could be due to air bubbles in pouring the plaster too fast. Another note I made was that the second thumb where I tapped the cup against the table did result in less air bubbles on the thumb surface.

Some potential issues: I didn’t realize that I shouldn’t leave the plaster for many hours due to it releasing water. I did, and while the thumbs ended up okay, it could’ve affected the internal integrity of the two casts.

First thumb air bubbles:

Second thumb less air bubbles:

Comparison of the two thumbs:

Cost Analysis

Alginate: $35 for 3 lbs. I used 9 oz of alginate –> 81 g.

81 g x (1 lb/ 454 g) x ($35 / 3 lb) = $2.08

Plaster: 2 oz x ($0.13 / 1 oz) = $0.26

 Labor: $15/hr x 2.5 hrs = $37.5

Total cost = $39.84

Conclusion/Insights

Molding and casting with alginate produces a high level of detail. Some concerns include air bubbles, and this could be mitigated by tapping the cup against a surface to make sure the plaster reaches all crevices. Removing the mold from the thumb was a focused process, as the casting might break if taken out too quickly. Overall, it was fascinating to produce two extremely detailed thumb castings using a relatively simple process.