Week 10
Assignments: Molding and Casting
group assignment:
• review the safety data sheets for each of your molding and casting materials, then make and compare test casts with each of them
• compare mold making processes
individual assignment:
• • design a mold around the process you'll be using, produce it with a smooth surface finish that does not show the production process toolpath, and use it to cast parts
• extra credit: use more then two mold parts
Ring Nuggets
Molding & Casting — Rings to Stamp Heads
This week, we looked at safety data sheets and instructions for Umu products, which were largely non-toxic and easy to apply. Safety instructions mainly just involved using a ventilated room, like our spray room, and wearing gloves and glasses.
This week, I decided to clone the faces of two of my rings, which used to belong to my dad. I thought that it might be interesting to translate these rings into stamp heads so that the green man’s face could become a textured ink stamp, maybe fitted onto a nice little chunk of aluminum, a small aluminum cylinder for a Christmas present. I started by creating a really simple jig so that they rest flat. This is easy: a popsicle stick, the same ones we’re using for mixing the two-part mix. I used Umu 25, which sets up in 15 minutes and cures within an hour, about 75 minutes. I measured out the dregs from three existing bottles on our table, which left me with a little bit more than what I needed to produce these molds, and so I decided to cast an almondine crystal as well.
I started by submerging the two rings in the majority of the mix up to a seam that captured most of the detail, and then I poured the remainder into a small vessel so that it could set up and produce a base for the almondine crystal to sit on (see the fourth photo). After that, I used the dregs of my dregs to cast a sheet on top of the brick I found, to study the strength of the material in brushed-on application. I’m curious to do this because I ultimately would like to cast an element of street marking—an arrowhead—for one of my lamps, and this was a test to see how possible that is.
Side note: by the end of the project, it was clear that I would need to study the interaction of silicone on silicone casting, silicone on moisture, and silicone in cold atmosphere. The cure time was very different for solid versus thin applications and seemed to be a bit more tacky at the end of a pour where perhaps it was less well mixed along the sides of the pouring vessel.
After all this, I repoured the almondine and let everything sit for a day. I came back and removed the elements, trimming the edges for the rings and then cutting notches down the side of the almondine until I could pull four sides apart and remove the crystal.
Then we dusted the molds with cornstarch and poured in a bismuth–tin alloy that is very heavy and very lovely because it’s low-temp casting, and demolded. The detail came out quite well. You can tell, without a vacuum chamber, that bubbles were rising up and getting caught in the texture of the rings, which means this material definitely works better when you pour over something rather than submerge it.
The only thing I would change is making a more complicated mold so that I could pour over these rings. It makes sense that I didn’t do this now, because it was so easy to get the project done with mostly the desired result by submerging them instead of pouring over them. In addition to casting the rings in the bismuth–tin alloy, I also cast wax into them and may think about how to use these waxes for something else. Finally, I inked and stamped them to see what they might look like without a flexible material.
Finally, I cast a batch of Sorta Clear 37 into the ring molds. This was fine; however, the silicone-on-silicone cure was impeded—everything was tacky and unpleasant—so I’m going to create a hard mold from the soft mold and invert it, so I can cast soft into that to produce the stamp heads I want. I have a feeling the texture of the silicone will be perfect, because it’s more rigid and harder to pour, so an additional molding step is ideal for doing the hard silicone.
