As a class, we created molds of our fingers using alginate and filled the mold with plaster. Unfortunately, we left the plaster in the molds for too long, allowing water from the alginate to seep into the plaster and weaken it. Then, when trying to remove the fingers from the mold, the plaster broke.

I had torn apart the mold trying to get the fingers out so it was time to make a new one. A group of us mixed a new batch of alginate according to the instructions, mixing 4 parts water to one part alginate by weight and filling the mixture into silicone cups (each cup had about 75 grams of alginate and 300 grams of water).

I held two fingers in the cups for a few minutes until the alginate solidified. When holding my fingers in the alginate, I was careful to make sure that my fingers were not touching the edges of the cup (so I would get a complete mold) and to keep my fingers as straight as possible so it would be easy to remove the plaster later. Then we mixed 2 parts plaster with 1 part water by volume (using a small cup to measure) and filled the molds with it. I tapped and lightly shook the cup to try to push any air bubbles out of the plaster. Two screws were then partially submerged into the plaster, being held up from sinking fully in by two pieces of tape (one piece for each screw). In the initial casting with the class, I had originally tried using one piece of tape for both screws, but it was difficult to get both the screws positioned properly at the same time. Learning from this, I individually positioned each screw in the mold with separate pieces of tape.

After letting it dry for 2 and a half hours, the fingers were carefully removed by pulling on the screws to create two molded fingers. One of the fingers I used has a scar on it and I wanted to see how well it would transfer to the mold, hence why one of the fingers has a line along it. There were also some small air bubbles on the surfaces of the fingers.

   

I tried making another cast using the same mold, to try to make identical copies since the mold still seemed to be intact. However, one of the fingers broke when trying to remove it and the other one had a lot of marks along the surface. It seems I did scrape up the mold a bunch when removing the first set of fingers. Alginate is too soft and not durable enough to easily make multiple casts with the same mold, in addition to the alginate warping as it dries.

   

So I went ahead with using the original two fingers I had created. Using a knife, I scraped off the extra pieces of plaster on the bottom of the fingers and smoothed out the bottom. I did not sand the surface of the fingers as that would ruin the skin pattern the molds reproduced.

Then I reused the alginate as a stand to hold the fingers. I stuck the fingers into the flat bottom of the alginate mold so that I could easily spray paint around the fingers. As instructed by the directions on the spray paint, I did two light passes of paint over the fingers, waiting a few minutes in between, before letting it dry for at least an hour. I then took the fingers out, covered the screws with tape, and painted the bottoms. I finished with two grey finger hooks of two of my fingers.

Cost Type	Cost	Price	Source	Quantity	Total
Materials	Alginate	$0.65 /oz	Dickblick.com	2.65 oz	$1.72
	Plaster	$1.94 /lb	Homedepot.com	0.09 lb	$0.17
	Silicone cup	$0.90 /cup	Amazon.com	1 cup	$0.90
	Spray paint	$6.19 /can	Target.com	0.1 can	$0.62
Labor	Molder/Caster	$15.75 /hr	Recruiter.com	0.5 hr	$7.87
	Spray Painter	$17 /hr	Ziprecruiter.com	0.25 hr	$4.25
	Prototyping Engineer (You!)	$39 /hr	Salary.com	0	0
Overhead	Facility Cost (Machine Time) (Power Drill w/ mixer)	$4 /hr	Homedepot.com	0.16 hr	$0.64
	Quality Control	$20.72 /hr	Indeed.com	0.25 hr	$5.18
Design	Engineering and Development		Covered in Prototyping Engineer		$0
	Iterations	Multiply total cost		x3
Misc.	Waste and Scrap		Covered in iterations, each iteration used about as much material as needed

For one pair of fingers: $21.35

Total Cost: $64.05