Glass Machining Expert Discribes Antique Scribed Edge

Glass expert had he opportunity to examine the edge of antique rolled, ground and polished window glass. This glass was removed from a greenhouse built in 1930. The window glass was sized by glass scribing and breaking it from a larger piece of glass. Above is a photomicrograph of the edge of the window. The glass cutting tool was run along the top of the glass. This created the "crush" damage indicated in the photomicrograph. This damage was driven downward to cause separation of the glass along a line. After sizing it appears as if the edges had been dressed by edge seaming. The crush damage is so severe that the seaming is all but invisible on the top of the glass pane. Also, the high degree of crush damage makes this piece of glass vulnerable to cracking. The glass pane performed well for over 80 years as long as it was held in its frame. After removal, it cracked due to thermal stresses. This photo illustrates that scribing and breaking creates two distinct edged. The "crush" edge and the final edge. The crush edge is where most later cracking occurs.

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