compatability between Art clay and coe 90 glass

[cstrang]

I've fusing dichro and bullseye coe 90 regularly and have just begun trying to make bails with low-fire slow-dry art clay 650.  Are there any reports about compatibility issues between the art clay and coe 90 glass?  

I fired the glass first, then made bails/wraps for the glass pieces. I dried and fired the art clay according to the package directions for the low-fire schedule (dry 20 minutes at 250F, ramp to 1350, soak 30 minutes, slow cool down for glass annealing) . The glass fractured after cooling, at the metal/glass junction on all four pieces.

Thinking that I might have just the clay wrapped too tightly, I re-fired all 4 pieces at a full fuse schedule –which was also within the range of the high fire schedule on the package directions (slow ramp to 900F, soak at 1450F for 5 min, slow cool). Because the pieces were ~1/4" thick, under 2" square, and cool down through 900F takes more than 10 min, i didn't do a separate annealing soak for either firing.  If it was an issue with shrinkage the second firing should have taken care of it, since the metal should have shrunk in the first fring.

The glass re-fused during the second firing, but 3 of the 4 pieces fractured again as I was buffing them.  This hasn’t been an issue when a friend has worked with the PMC 3. Should i just switch to PMC 3?  Does anyone have suggestions about firing schedules that will avoid glass fracturing?

[Metalman]

I have done a fair amount of ACS and glass firing. Ultimately - I do not think that the silver clays are 'compatible' with the glass. That said, I have had good luck with glass and ACS fired together. I usually fire a footing using overlay paste on the glass [1st firing]. 

Then I build my clay fitting/finding/etc., and attach with paste [& usually some overlay paste] then fire again [2nd firing].  Frequently - at this point there are a few repairs to be done at the glass/silver interface - but they are in the clay [not the glass].  So - I repair and fire a 3rd time - usually good at this point.

I think that if you build with large areas of contact - you will have expansion/contraction problems which are usually what we refer to as compatibility problems.  I have found that if I set the design up for contact or point fusing [does that make sense?] then the glass and the ACS do just fine.

I cannot address the PMC3 question as I have not used the product.