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I've been firing dichroic/fused glass along with PMC and have been getting a brown scummy discoloration in the glass - this seems to happen in 2 ways:
1) when firing glass in direct contact with the pmc the discoloration is where the glass & pmc meet
2) when firing glass in the same firing but not in direct contact the glass will get a ring of brownish discoloration about 1/3 of the way from the edge to center of the glass

I'm going to try firing the pmc first then re-firing with the glass attached, but meanwhile I'm curious - does anyone know whay this may be happening? I wonder if the binder that burns off as the pmc is fired gets into the glass through the air? Should I avoid firing the 2 together?

Thanks for helping!

hi!
when i took a pmc class, i was told that the pmc interacts with regular "clear" glass and that to avoid this it was necessary to use a specific be clear to avoid this discoloration. sorry, i don't remember the be # for this glass, but a pmc dealer should be able to provide you with this info.
which pmc are you using? if it's not the one for use with glass, you may be having to fire too hot or too long (for the pmc to do its thing). resulting in discoloration for glass.
are you firing the two together for a fuse + setting in one step? my understanding is that you should be firing the glass first, then second firing with glass in the pmc.
because of its shrinkage, it you're using pmc to create the setting for the piece, like a bezel that surrounds and holds the glass, you have to fire the two together for the pmc to shrink into place around the glass. fire glass first so you know shape/size, then apply and design the pmc around the glass then second fire.
could it be that you're getting oil or ?? from your hands on the glass before firing?
hope some of this helps. also, check pmc website for lots of tips.
linn

rshepher wrote:I've been firing dichroic/fused glass along with PMC and have been getting a brown scummy discoloration in the glass - this seems to happen in 2 ways:
1) when firing glass in direct contact with the pmc the discoloration is where the glass & pmc meet
2) when firing glass in the same firing but not in direct contact the glass will get a ring of brownish discoloration about 1/3 of the way from the edge to center of the glass

I'm going to try firing the pmc first then re-firing with the glass attached, but meanwhile I'm curious - does anyone know whay this may be happening? I wonder if the binder that burns off as the pmc is fired gets into the glass through the air? Should I avoid firing the 2 together?

Thanks for helping!

i've been playing with pmc a bit here and there - linn is correct in that often crystal clear be is best when making fused pieces to use with pmc, pmc 3 is the best version to use with glass and fusing the glass first then adding the pmc and firing it to that specific temp is the best way to do this - have you bought any pmc books? the one for working with glass and pmc is the one by mary ann devos....
D