calculating the weight of glass for pot melts.
- February 5, 2014 at 11:00 pm #10091
I am trying to make pot melts and I am using the following formula (all metric):
volume x 2.5 = weight. Example: 12 in circle, 6mm thick:
12 in = 30.48 cm (area = 15.24 squared x pi (3.14) = 752.44 sq. cm) x .6 = 437.57 cu. cm.
437.57 x 2.5 (specific gravity of bullseye glass) = 1,094 gms.
I put slightly more in the pots due to left over and followed the Fused Glass.org pot melt schedule (top process temp 1700 degrees) and I got about 2/3 or less of the 12 ring filled.
What did I do wrong? I am planning to use a lot of scrap glass for pot melts and I don’t want to waste it.February 7, 2014 at 3:21 pm #13247JeaniceParticipant
1094g is correct. Maybe the error happened when you weighed the glass? Is there a way you can calculate how much glass was left over in your pot? Think I read somewhere to add 5% to 10% extra glass to account for the glass that remains in the pot.
Hope this helps. Hopefully someone else with more pot melt experience will come along.February 7, 2014 at 5:19 pm #13248betncaParticipant
I don’t have an answer but you are not alone. I have done three pot melts and had the same results that you did. I double- checked everything including my scales. I thought I might need new scales but that wasn’t the problem.February 8, 2014 at 10:44 pm #13249AnonymousInactive
How thick is the pot melt in the middle? It takes a while for glass to fully spread to a full 12 inches. If the glass is even a little thicker than 6mm that would explain it not being 12 inches across.
When I make pot melts I include a 30 minute hold at 1500° F on the way down.
Helios Kiln Glass Studio
PaulTarlow.comFebruary 10, 2014 at 8:23 pm #13250
I’ll try that.March 5, 2014 at 4:51 pm #13251
I tried again with similar non-acceptable results. I put about 25% more glass into the pot, fired at 1700 for 90 minutes, 1500 for 60 minutes, 900 for 3 hours and continued to cool slowly. I measured enough glass to have between 8 – 9cm. I also got tons and tons of bubbles. I don’t want to give up but I just don’t know what else to do.March 8, 2014 at 8:44 pm #13252Stephen RichardParticipantMarch 9, 2014 at 3:49 pm #13253betncaParticipant
I have had the same problem on 3 melts so haven’t done any more. What math formula did you use? I thought maybe my scales were off. Do you have a particular way of arranging the glass to weigh it?March 10, 2014 at 8:31 am #13254Stephen RichardParticipantMarch 10, 2014 at 4:19 pm #13255
I tried again with french vanilla, white, medium amber, and clear and weighed just about 1700 gms. I had a “stopper” in the dam so that I would have a hole in the glass (3.5 inches in a 12 inch dam) which I later filled with a piece made with murrini. 500-1700-2hrs, full-1500-1 hr, full-900-3hrs, 100-800-0, 200-700-0, 300-100-stop. I have a beautiful piece of glass although the stainless steel dam was warped. I re-fired at a full fuse with the extra piece, and although the edges need a lot of coldworking, the end result is more than I hoped for.
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