Originally Posted by raspero
This is fascinating. The molding is not so far from what I do, but yet very different—working in fired clay and concrete. It's a different world.
Some seem to like fiberglass for mother molds, I don't, I normally just use whatever casting plaster I use for casts, used to be Hydrocal but the past few years I use a rival brand to USG called Densite, and it's stronger and harder. But lately when I get a shipment of Densite I order 2-4 bags of pottery plaster to use for shells, it's goes a little further per pound and it's slightly lighter.
I also took the second fired panel out of the kiln, they are coming out good, no cracks or warp but I'm finding two issues, one is, setting them directly on the floor of the kiln is not allowing that area of the sculpture on the edge, going in about an inch or so develope the same color as the rest, it's slightly lighter. So to correct that I'm going to place them on some posts laid flat so they are about 1-1/2" off the floor of the kiln.
The other issue was even reducing the temperature from 2079º to 2060º I'm tending to get the brown color more instead of the red, a ∆1 I put in on th emiddle shelf actually bent over, so it would seem the kiln is firing hotter than what it's set at, so i've made a small adjustment to the firing schedule, reducing the temperature 10 degrees to 2050º and changing the 10 minute hold to 5 minutes:
R1: 90º/H to 200º
Hold for 9 hours @ 200º
R2: 60º/H to 1200º
R3: 100º/H to 1860º
R4: 60º/H to 2050º
Hold for 5 minutes
Next firing I do I'll see how that change works out, I guess I will get some ∆1 cones and some ∆01 cones and start monitoring to see. The 01 should bend way over and 1 should not bend, if it does it's getting hotter than I want.