Molding and Casting: The Index Finger

In this project, we learn how to use molding and casting techniques to create wall hooks of our own fingers. This project makes use of unique material properties as well as the principle of creating and using molds to replicate existing shapes in a plaster/concrete form.

The creation of each hook requires two general steps: “negative” mold creation and “positive” casting. To create our molds, we used a peculiar powder called alginate, which, when mixed with water, formed a gooey liquid. After stirring the liquid alginate, we placed our fingers into the liquid and waited for it to dry sufficiently. Then, we were able to carefully remove our finger from our mold. The casting process involved mixing the plaster with water and pouring it into the mold of our finger. The finishing touch to creating the wall hook was placing a screw into the plaster so that it would dry alongside the cast of the finger.

Plaster Finger

When starting my first mold and cast, I followed the procedure closely by mixing the alginate, creating the mold of my index finger, and then pouring in liquid plaster. I let this dry for a little over an hour, and when I removed the alginate, it looked very nice! I was surprised with the amount of detail that the mold would have, and even more surprised that the detail carried over into the plaster cast. The plaster hardened into a slightly rough, white material, but it was detailed enough to clearly show my fingernail and some skin details.

cement Fingers

Later, I wanted to create another successful cast of the same index finger. This new alginate was slightly different, and I also used cement rather than the plaster. Because I was less familiar with these different materials, I chose to make two more molds to allow for some iteration. My second mold worked well, but I encountered some difficulty with the cement

being too thick to pour into the mold. When pouring the cement, I specifically noticed that some air was getting trapped beneath it inside the mold. To alleviate this, I was able to use a popsicle stick to stir within the mold and release some of the bubbles. After 90 minutes, I opened up the mold and made two observations. First, the cement had not dried at all like the plaster, so the finger broke very quickly. However, I was pleased to see that I had removed almost all of the air bubbles before.

I approached the second cement finger with a better understanding of the materials. I completed the mold, and I mixed the cement with more water until it reached a more liquid viscosity. This better allowed me to pour into the mold without forming air bubbles. Then, I let this one dry for 7 hours. I opened this mold much more gently, but alas, this finger was also broken in half. While the extra drying time had certainly allowed the cement to harden, the moisture inside the alginate still made the cast fragile. Otherwise, I was happy with the quality of the finger itself, and I was glad that my second iteration with cement was better than my first.

Cost Analysis

Plaster of Paris (one finger):

5 ounces, $0.042 per ounce: $0.21

Alginate (three molds):

10 ounces, $0.73 per ounce: $7.30

Cement (two fingers):

10 ounces, $0.15 per ounce: $1.50

Total:

The cost of materials came out to $9.01 for the three casts.

 

-Kenton Roberts