Remember way back when I did a silicon mold of Marla's hand and forearm?
That mold was thing, but seemed okay. The plaster shell on it was very nice, though.
Yesterday I poured two pounds of Evergreen polyurethane rubber into it. This is a thin rubber, with good flow, and a light fruity odour. Hardens up to Shore-A 40, firm yet still flexible.
It seems that I filled the arm up beyond a split in the mold silicon, so a fair amount of rubber leaked into the plaster shell.
Did I mention that polyurethane rubber has intense adhesive properties when applied to anything except silicon? No? Well, it does.
After destroying the plaster shell (sob!) I proceeded to peel the silicon off the rubber. It release very nicely.
However, rolling the wrist back off of the hand proved troublesome. Ultimately, the silicon mold broke taking it off the poly hand...
Further experiments show that the body double silicon has maybe 50% to 75% useful stretch, but needs probably 100% to open the wrist up around the hand.
This strain was further exacerbated by the spotty mold itself. It had many thin spots. It turns out that there were also flaws in the silicon, following two trends.
One is the everpresent bubble, which I can get rid of by more careful application of the silicon.
The other was wet/dry seams. Adding new silicon to a section that has already cured created a number of seams, where the blending was imperfect. To fix this, I'll need to take more care in my application pattern, and to be SURE to have someone manage the material gun so I can focus on application.
The detail, on the non-bubbly or seamed parts, is excellent in both the silicon mold and the poly hand. My next step in this lengthy experiment is to make a solid plaster negative in two parts, a clamshell mold for the hand.
Once I have this, the final, ultimate goal is to cast a silicon Dragon Skin hand/forearm around a set of modified Bucky bones.
This will reproduce last year's experiments with this technique, using these new, better materials and methods.
I'm not getting perfect results yet, but I hope to get at least excellent results on the second pass through... when I make the final props.
Posted by Edwin at June 28, 2004 03:35 PM