Overview

For this assignment, we had to create alginate molds of one of our fingers and use those molds to cast a plaster replica of the fingers. After the plaster fingers were produced, we post-processed and finished them to seal off the plaster and give the fingers artistic flair.

Initial Molding and Casting

I started by creating an alginate mold. Alginate is a cheap, seaweed-based material commonly used to create molds of body parts for recreation or teeth for dental devices. We mixed about 30 g of alginate into 125 g of water, then poured it into a silicone cup. I then dipped my finger into the cup and waited. I accidentally overmixed mine, so it didn’t cure properly. However, for the sake of the in-class tutorial I made a cast with the mold anyways.

I mixed 100 g of plaster with 50 g of water, then poured it into the hole left behind by my finger. I inserted a screw into a plastic strip with holes that I then set on top of the plaster. This would allow the finger to be screwed into the wall. I came back the next day to remove the hardened finger from the mold. Because the mold was not properly made, the plaster finger was weirdly lumpy and misshapen.

Second Try

I made a second alginate mold, this time increasing the ratio of alginate to water (20 g alginate and 70 g water) and making sure not to overmix. I dipped the same finger I used the day before and allowed the alginate to cure. Once cured, I mixed 40 g of plaster and 20 g of water (the original amount was too much for one finger), poured the mixture into the mold, and inserted another screw. I came back later in the evening to remove the plaster finger which turned out significantly better than the first attempt. My mold was still intact, so I mixed more plaster and poured it into the same mold, repeating the step to add the screw.

Final Painting

After demolding both fingers, I lightly sanded the rough edges and spray painted them. I started with a layer of grey primer, then added 3 coats of green spray paint (the same green I bought for the metal diamonds homework). Once the green layers dried, I added a clear gloss coat.

Cost Model

Cost Type	Cost	Price	Source	Quantity	Total
Materials	Alginate	$49.39 /3 lbs	Amazon	50 g	$1.82
	Plaster of Paris	$6.64 /4 lbs	Home Depot	200 g	$0.73
	Wood Sticks	$4.99 /200 pcs	Amazon	6 Sticks	$0.15
	Wood Screws (1.25”)	$9.98 /box (184 screws)	Home Depot	3 Screws	$0.16
	Assorted Grit Sandpaper	$7.99 /36 sheets	Amazon	1 Sheet	$0.22
	Primer	$5.98 /can	Home Depot	1 Can	$5.98
	Green Spray Paint	$28.74 /6 cans	Amazon	1 Can	$4.79
	Clear Coat	$5.98 /can	Home Depot	1 Can	$5.98
Labor	Prototyping Engineer	$36 /hr	ZipRecruiter	1 Hour	$36.00
Overhead	Makerspace Access	$40 /month	The Maker Barn	2 Days	$40.00
Total					$95.83

 

For this cost model, I classified materials as consumed items. Equipment such as scales, cups, and spoons that are all reusable were included in the makerspace access fee. Including access to an entire makerspace here was likely overkill because most people have cups and spoons in their homes, and the scale made the process more precise, but was not actually necessary since the instructions on the bags for the alginate and plaster both used volumetric measurements. For the labor, since there was very little labor or prototyping that needed to be done, I included all the work as just 1 hour for a prototyping engineer. Labor and overhead were by far the most expensive part of this assignment, and even those numbers were vastly overestimated. The actual materials only cost $19.83, and that is assuming I used a whole can of each spray paint (which I did not need to do).