Weak areas on irid side after mold/fire polishing that created holes.

[tomodachidesigns]

I decided to use scrap dichroic glass with irid side down, topped with clear glass, then fused in a dam mold. After, I cut my glass and fire polished them, everything looked great, except that I noticed weak spots in the irid side and which created a shallow hole.  My question is, does the irid side become brittle after a few firings?  If so, should I use clear glass on the bottom of the mold and this would correct the problem?  Love to hear your theories.  Thanks!

[Stephen Richard]

I need some more information.  I do not know what you mean by “week spots in the irid side.”  Could you expand on this with a description?

The iridised and dichoric coatings do not become brittle, but do “crinkle” more on subsequent firings as the coating does not expand and contract in the same way glass does.

Stephen Richard

blogs at: http://www.verrier-glass.blogspot.com/ and  http://www.glasstips.blogspot.com/

[tomodachidesigns]

Stephen-  I don’t think it’s a crinkle.  If I were to press on the irid side after a couple of firings, it would create shallow hole. (like a crater)  If I knew how to post a picture, it would be easier to explain.  Let me know what you think.  Thanks for responding.

Paulette

[Stephen Richard]

I have re-read your original post.  I bet that you are using thinfire as a separator.  This gives exactly the result you described in the second post.  The irridisation reacts with the thinfire to produce this cratering, so you must never fire irridised glass in contact with thinfire.

Stephen Richard

blogs at: http://www.verrier-glass.blogspot.com/ and  http://www.glasstips.blogspot.com/

[Anonymous]

Actually, you can fire irid on Thin Fire one time without problems.  It is the 2nd (and subsequent) firings that will cause the bubbling between the glass and irid.

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Paul
FusedGlass.Org
Helios Kiln Glass Studio
PaulTarlow.com

 

[Stephen Richard]

I must have done something wrong. It happened to me on the first firing.

Stephen Richard

blogs at: http://www.verrier-glass.blogspot.com/ and  http://www.glasstips.blogspot.com/

[Anonymous]

Not sure – but we fire Bullseye irid down on Thinfire all the time without an issue – we just don’t do it twice.

Are you using Bullseye glass and their shelf paper?

Also, what’s under the shelf paper (shelf, fiber paper, fiber board?)

Lastly, what temp are you fusing at?

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Paul
FusedGlass.Org
Helios Kiln Glass Studio
PaulTarlow.com

 

[tomodachidesigns]

I am using the thinfire and bullseye thin in the mold then placed on top of the shelf and firing at 1470 for my initial firing. After cutting out my designs, I polish fire at 1250, since 1200 just doesn’t do the job to my satisfaction. So after your comments, I’m just wondering if I could use non irid glass as the base, topped with irid/dichro glass, then a clear cap. This shouldn’t make my piece brittle, right? Thank you so much for your input.  Paulette

[Stephen Richard]

Firing Bullseye on Thinfire above sand or ceramic shelf to 804C

Stephen Richard

blogs at: http://www.verrier-glass.blogspot.com/ and  http://www.glasstips.blogspot.com/

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