Making up this assignment was a lot more difficult than I expected. First, locating the alginate was a trip of itself – after a couple of days of checking with Lab Techs about trying to find some, I asked Adulfo where to find it, and I’m embarrassed to say I should have checked under the ENGI 210 work tables first. It’s also where I found the quick-dry cement (“quick-dry” my butt, but we’ll get to that later).
Attempt 1
Making the mold was surprisingly easier than my initial anticipation. After making the alginate mixture (1:1 ratio of alginate to water), I stuck my left pointer finger to mold so that I could still use my right hand to multitask. It must have been weird for the TAs to watch a student walk around with their finger in a cup while checking on Carvey’s progress. After removing my finger from the first mold, I mixed a second batch to make the next mold, following the same process.
Once both molds were ready, I mixed the cement with a 2:1 ratio of cement to water as listed in the instructions, then poured the cement into the mold (in hindsight, the liquid-y consistency should have been a clue that this would take longer to set than I expected). I think if I made a smaller batch of cement and poured only enough to fit the finger mold instead of covering the top of the mold, the product of this first attempt may have gone better. I then inserted the screws at the top of the mold.
The result of this mold was such a crumbly mess, the fingers fell apart as I tried to demold it. Not the conclusion I was expecting for attempt one.
Attempt 2
For this attempt, I tried to learn from my blunders. I used a bigger container and stuck two fingers in the alginate simultaneously, using the rock-on symbol. For the cement, I eyeballed the ratio this time and made sure that the mixture had a much thicker viscosity in hopes that the fingers would set faster. I also made a much smaller batch and made sure to pour only enough to fit the molds (no overflow this time). I then waited 14 hours before attempting to demold the fingers.
At this point the cement felt hard and seemed like it had set, but the nails fell out. For demolding, I used a xacto knife this time to shave off chunks in an attempt to not disturb the fingers.
The cross-section makes the alginate mold look like cake
The first finger split in two, and quite honestly looked like poop pellets. I did have a little more success with the second finger, but not by much.
First finger – the poop pellets
Second finger – some improvements, though I wished the nails actually stayed in
After reading other students’ posts about their struggles and mishaps, I felt immensely better about my failures. In the future, I’d probably choose a different brand and type of cement.
Cost Analysis
– Labor: 2.5 hours at $15/hr = $37.50
– Alginate: $49.99 for 3 lbs., 1 lbs. used = $16.66
– Concrete: $5.25 for 50 lbs., 1lbs. used = $0.10
– Other materials: paper towels, nails, popsicle sticks, etc. = ~$1
Total cost: $55.26
