Last week, we learned how to do molding and casting, and this was my first experience. We aimed to use our fingers as a model to make a wall hook. We followed Dr. Wettergreen and TA’s instructions and started the work.

My first step was to make an alginate mold of my fingers. Below are the steps I followed:

• I took a silicone cup and added 33g of alginate powder.
• I added 125g water into my silicone cup and mixed alginate and water together by using a popsicle stick.
• After mixing thoroughly, I put my left index and middle fingers into the mixed alginate.
• Kept my fingers in the alginate for five minutes until the alginate solidified.
• Pulled out my fingers and the finger mold was complete.

The second part of the process was casting. Here are my steps:

• I installed two screws on the jig and put this into the finger mold cup I just made so that the screws fit into the hole of the fingers. At this step, I found that I put my finger too close to the edge of the cup, so when I put the jig into the cup, the shape of my fingers was slightly deformed because the jig stretched the rim of the silicone cup.
• Mixed plaster of Paris and water in a 2:1 ratio. As I wasn’t sure how much plaster I would need, I added 35ml of water to another smaller silicone cup and then added the plaster powder until the proportions were correct.
• Mixed the plaster using another popsicle stick. At this point, I had about 70ml of plaster to add to my finger mold.
• The last step was to add plaster to my finger mold and wait a day for it to set. At this point, I realized I had prepared too much plaster, and nearly half a cup was left.
• Below are pictures of the powder and cups we used:
  

One day later, it was time for de-molding. I thought this was the most challenging part. Before I started de-molding, I met some classmates who failed to de-mold and caused the finger model to break.

• I took the alginate out of the cup as carefully as possible.
• I slowly pushed aside the alginate and successfully removed my finger model, but it was still wet and felt fragile.
• I put the finger model on paper to dry, but my finger model fell off the screws. I thought my screws were too close to the edge of the finger model, so there wasn’t enough plaster to hold the screws in place on the fingers. The good news was that my finger model had a clear texture, except for some tiny bubbles.
• Below are pictures of my finger model after de-molding:
  

Post-processing:

• I super glued my fingers back onto the screws.
• I chose a color spray paint called French lilac to paint my fingers because I think this purple color is gorgeous. I sprayed the color spray twice to ensure that every angle was evenly colored.
• Finally, I sprayed it with a clear spray to give my finger wall hooks a nice shine.
• Below are pictures of post-processing and my final product:
  

I learned a few things in this course.

• Maybe because of the rainy day, the plaster model we took out the next day felt wet and fragile.
• My plaster model has bubbles. Maybe it’s because I let too many bubbles in while mixing it. Next time, perhaps I can tap it before pouring the plaster to let the bubbles out first.
• Next time, I can check the position of the screws and jigs first and then put my fingers in the right position to make the mold to avoid pulling and deformation.

The cost analysis table:

Cost Type	Cost	Price	Source	Quantity	Total
Materials	Silicone Cup	$8.99/2Pcs	Amazon.com	2	$8.99
	Screws	$7.21/50Pcs	Amazon.com	2	$0.2884
	Jigs	$2.35/10Pcs	Ebay.com	1	$0.235
	Alginate	$18.25/1.75lb	Amazon.com	0.073 lb	$0.7613
	Plaster	$11.79/2lb	Amazon.com	0.154 lb	$0.9078
	Spray Paints (Purple, Clear Coat)	$5.98/12Oz	Amazon.com	1 Oz of purple, and 1 Oz of clear	$0.9967
	popsicle sticks	$4.99/200Pcs	Amazon.com	2 pieces	$0.0499
Labor	Prototyping Engineer (Me!)	$36/hour	ZipRecruiter.com	2 hours	$72
Overhead	Outdoor	$0	None	–	$0
Misc.	Waste and Scrap	$0.66/Gal= $0.17/L	Houstontx.gov	0.2L	$0.034
Total	$84.2631

Picture of our clean workspace: