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artfem
Administrator
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Sun Mar 16th, 2008 11:34 pm |
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The concept of cross-weaving lead to make a stronger leaded panel is based on two primary concepts: equal distribution of the stress on the panel results in a longer life for the panel; and breaking hinge joints with through leads makes the panel stronger. I have seen evidence that this works in many windows that I have worked on over the years. The science behind it is strong as well. Virtually all constructions are as strong as their weakest links. When the stress is more evenly distributed throughout a leaded panel, it will last longer. This has no affect on complete copper foil windows for obvious reasons.
Tucking flat leads is another way to make a window stronger. When the lead is tucked within the lead it is joining, a sweated solder joint is formed. Based purely on surface area of the soldered joint, this is a much stronger construction than depending on the surface area of a butt joint. Further, a sweated joint allows for a thinner application of solder. This benefits the panel in that the joint is more flexible and does not create a hard spot in the window at which the flexing stresses of the lead came matrix are focused resulting in premature failure of the solder joint.
There has been mention of leads being compared to columns and the effects of gravity not being well resisted by a panel that is cross-woven. A number of points should be considered. First, gravity has very little to do with the failure of a leaded glass panel (assuming the panel is installed vertically and not a lay light). We have all seen panels that are just as deflected at the top or in the middle of the panel a they are at the bottom. The force exerted by gravity is always greatest at the bottom of the window due to the greater mass of the window that has to be supported. If gravity was the prime culprit, we would always suspect to see the worst damage at the base of the window, this simply isn’t true.
The greatest force working to distort and deflect the lead came matrix is the force generated by the expansion/contraction cycle. If you run the numbers, science bears this out. The forces developed in a typical window setting due to expansion can be ten times greater than the forces developed by gravity. This is why cross-weaving is done, to strengthen the window against the flexing forces (which are perpendicular to the lead cames) and not gravity.
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glasman
Director
| Joined: | Mon Jan 7th, 2008 |
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| Posts: | 59 |
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Posted: Tue Mar 18th, 2008 10:30 pm |
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Last week, I looked at some Mayer of Munich windows that I conserved approx. 25 years ago. [St. Mary's cathedral, Norfolk, Va.] Despite dating from around 1890, and being glazed with extremely thin flat leads, they still don't need releading.
All the leads are tucked.
John
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