Broken glass

[Backwoods Savage]

This is part of an email I received from a friend who live a long ways from me. I sent off my first thoughts to him but wondered of someone else might also have some thoughts different from what I told him. Here is part of the email:

"I broke my fireplace door window a couple weeks ago. The new glass that I replaced had to be tempered for a week. He mentioned after a week it should be fine. When I got home tonight it was cracked. I noticed the metal that holds the window in is the only place that cracked or the glass cracked I should say. Do you think the metal gets hotter then the fire and it cracked the glass? It appears maybe the rope that separated the glass from the metal was about a 1/4 inch off of the the glass too which allowed for more glass on metal. Hope this makes sense. I'm completely frustrated right now. Waited a week for new glass. Ran small fires for a week to temper the glass and now it breaks. "

Sounds to me like a poor fit for sure but what about this tempering for a week?

 

[Corey]

This is part of an email I received from a friend who live a long ways from me. I sent off my first thoughts to him but wondered of someone else might also have some thoughts different from what I told him. Here is part of the email:

"I broke my fireplace door window a couple weeks ago. The new glass that I replaced had to be tempered for a week. He mentioned after a week it should be fine. When I got home tonight it was cracked. I noticed the metal that holds the window in is the only place that cracked or the glass cracked I should say. Do you think the metal gets hotter then the fire and it cracked the glass? It appears maybe the rope that separated the glass from the metal was about a 1/4 inch off of the the glass too which allowed for more glass on metal. Hope this makes sense. I'm completely frustrated right now. Waited a week for new glass. Ran small fires for a week to temper the glass and now it breaks. "

Sounds to me like a poor fit for sure but what about this tempering for a week?

I think he got the wrong glass. A fire in a fireplace will not effectively 'temper' any normal glass. This requires a strict heating and cooling regimen that will not be met by a couple of fires in a fireplace. True tempered glass (which should be a minimum requirement) would not crack - if anything at all, it would shatter into thousands of small bits. If he had true transparent ceramic (which would be ideal) there would be no need for any tempering fire. It will take the heat right out of the box, and really, the minor amount of heat a fireplace screen sees is nothing for ceramic.

One way to tell should be to look at the edge of the glass against a white background (sheet of paper, etc) If the edge of the glass looks green and it cracked, that is the wrong glass - normal annealed glass. If it is green and shattered into tiny bits, that is tempered glass. If it is relatively clear, that is transparent ceramic. In the latter two cases tempered or ceramic, it 'might' be an issue with poor fit or the glass being clamped too hard, but those don't really fit with the description.