Basic priciples:

By using a liquid that hardens either through evaporation or through chemical reaction, you can make a container shaped (almost) exactly like the object you want to make a copy of. Or rather, a negative of your object, like making footprints in cement. This is called a mold. Then, you can take that container and fill it with another liquid that hardens. As long as the two solids can be separated (usually a difference in elasticity is helpful here), you can have an exact replica of your object, with minor defects from air bubbles or material flaws. In this assignment, molds were made from my fingers, using alginate, then filled with plaster and a wood screw so it could be used as a wall hook.

First attempt:

In my first attempt, I actually accidentally used plaster instead of alginate to take the negative of my finger. Fortunately, one of my peers caught my mistake before I had my hand plastered to a disposable cup.

Second attempt:

Next, I made sure to use alginate, but my plaster was too liquid. I added more plaster powder, but I either added the plaster too late or tried to extract the mold too quickly (it had only been 30 minutes).

third attempt:

This time I read the plaster instructions very carefully and even added a bit of extra plaster powder. I waited two hours before extracting the plaster, and it worked! I wish I had made the mold bigger.

fourth attempt:

For this one, I had to use the darker plaster since the original container was empty. I was worried that it would have different rations because the bag was torn over the instructions. Luckily, the ratio used before (2 plaster to one water) worked fine, though it was a little thicker at the beginning. I had to drop the mold lightly on the table to make sure the plaster was fully filling the mold. But it was my cleanest mold so far, with few bubbles.

Cost analysis:

I tried to use the small rubber cups of alginate for my molds. Alginate is $7 for 13 oz.

Each mold took 1.5 oz of alginate, or $ 0.81. In total, I used $2.42 worth of alginate. Note that the first attempt used no alginate.

I probably used too much plaster for the first mold. Plaster is $7 for 4 lbs. This means that it is $0.28 per fluid oz.

first attempt: 5 oz

second: 3 oz

third: 1 oz

fourth: 2 oz

for a total of 11 oz or $3.08.

I spent 10 minutes on each molding/casting. Using my rate of $21 an hour, I spent .75 hours or $15.75.

So before labor that’s a total of $5.50, and after labor $21.25.