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Stained Glass/Thermal Expansion


Hi David,

I am thinking of making a window panel to fit an existing window.  How do I make allowances for thermal expansion?  It gets really hot here in Africa and I don't want the panel cracking due to the heat.  I am thinking of using copper foil and lead came as the frame.

Thank you for your invaluable contribution to this site.


Copper foil is fine for the body of the panel, but I would use zinc outer bar for the framework, lead stretches, so doesn't make a good frame.

In a hot climate you will actually have less thermal expansion than in a cool one. The reason is that colored glass holds all the colors into it except for the ones it lets through. A piece of blue glass absorbs all the light except for blue which it transmits. The held light turns into heat and so the glass gets hot. In a hot climate, the difference between the glass temperature and the surrounding air is less than the difference in a cold climate, so there's less chance of thermal shock.

All stained glass can get cracks over time. One trick that we've learned to avoid stress cracks has to do with the edge of the glass. Use a fairly smooth grinder bit. A rough "speed bit" will chip the edge of the glass which weakens it and can become a source of weakness.

If your window is going to go into a frame and actually fit the opening, you don't need outer bar on the panel. Simply use silicone caulking to hold it in place leaving a 1/8" gap around the glass. Examples of us installing panels can be seen at

Good Luck. Let me know how it goes,

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David Gomm


Copper Foil stained glass panels are our specialty. Both architectural and residential questions can be asked. We build windows and teach classes in our studio. We design custom patterns by hand and then draw tham using AutoCAD. We recently donated over 100 square feet of glass to the Covey Center For The Arts in Provo, Utah. I write a monthly newsletter that gives tips and tricks for the stained glass trade at We also teach classes because the joy of new stained glass students rubs off on us and keeps the hobby fun.


Started business in stained glass in 1983. We build and design architectural and residential stained glass and we write a monthly stained glass newsletter at We also install glass, fuse panels and produce instructional videos. Jeanne's first book on Mandalas For Meditation is available on Amazon and she's working on a second. David is halfway done with an instruction manual. Together they have produced 6 instructional videos on projects and techniques.

Utah County Art Gallery, David is webmaster, Jeanne is recording secretary. Utah County Art Guild, showing members. Covey Center For The Arts, Donors and volunteers. Heritage School, Donors.

Go Articles, Ideamarketers, and Ezine Articles. We also contribute to newspapers and ezines. Also have several videos on You Tube betterstainedglass assorted videos.

Bachelor of Arts in Education, Missouri Southern State University. Taught stained glass college course at MSSU, currently teach classes in our studio. Write monthly newsletter. Seminars in advanced lamp design, drafting and design, and glass fusing.

Awards and Honors
St. Francis Of Assisi Merit. UDot Mural Competition-2011.

Past/Present Clients
Covey Center For The Arts. Heritage School. Finer Consigner. Larry H. Miller. Keith Barton. UVU Alumni Association. St Francis Catholic Church.

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