Friday, April 20, 2012

Webmaster Marshall Ketchum adds more comment on heat checks

Alan

The subject of “heat checks” can take several turns. While they are most often noticed where handles are applied they can occur anywhere two pieces of hot glass were attached. A heat check does not need to occur while the piece is still in the factory it can occur days or weeks or longer afterwords. It depends entirely on how well the temperature coefficients of the glass matched when attached and how accurately the annealing process was determined and followed. The poorer the coefficient match or the poorer the annealing process then the more likely that heat checks or outright breakage will occur. Heat checks can be different from actual damage cracks. I had a couple of 3551 parfaits that had heat checks where the foot was attached and could only be seen by looking down the length of the parfait. The heat check could be seen because its index of refraction was different from the glass but it was buried within the glass and could not be felt from either side. It took the form of a tight circular crack within the glass.

I still tend to believe that some/many heat checks can be more acceptable than most cracks caused by damage.

Marshall

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2012 Carder Steuben Club annual Symposium will be held at The Corning Museum of Glass in Corning, NY from September 20-22, 2012.