Tempered glass needs to surround decorative glass used in a door. This protects people from injury if the glass is broken and it also serves as a barrier against heat loss during cold months. Tempered glass must be ordered in advance and once its been tempered, it can't be cut or ground. (there are pictures that were taken to illustrate this article at http://www.betterstainedglass.com/Newsletter/Archives/2006July-windowindoor/howtohangindoor.htm
#1 Here the panel is lightly cleaned to get any dust off of it that may have collected after you take it to them. They only do a light cleaning, you are responsible for making sure that it is as clean as possible when you take it to them.
#2 Next, the tempered glass is sent through a machine which “super cleans" and dries it.
#3 The stained glass is next laid out on one sheet of the tempered glass. It is centered and there is a gap on each side and top and bottom of 5/16" (the size you subtracted from your finished size when building your panel).
#4 Now, a sticky backed, foam tape with a metal skin is applied to the stained glass panel and the tempered glass below. It sticks to both pieces and holds them firmly.
#5 The metal tape is scored on each corner so it can be folded around the corner with a sharp clean edge. The tape can vary in width, this tape is 1/2", (we recommend 1/4" since the air gap will be less noticeable and the final width of the piece will be 1/2" total.
#6 Laying the second sheet on the foam tape requires help because they only get one chance to do it perfectly. Once the top sheet touches the tape, it's stuck. For this reason, you should always allow for an extra 1/8" in the finished opening of your door, in case the two sheets are slightly misaligned.
#7 Finally, the completed “sandwich" of glass is clamped in a table and hot butyl rubber is forced between the two sheets of tempered glass and filling the gap between the two. This covers the foam tape completely.
#8 Here, the completed window is ready for the customer to pick it up and to install it in their door.
Finally, the completed panel is installed in the door and it looks great!
To correctly size a window, we recommend the following:
The decorative panel should be sized 1" smaller than the actual opening in the door. This allows there to be enough space for foam tape in the bottom of the opening to support the window and for silicone in the sides and top to hold the panel securely. The tempered glass (ordered in advance from the glass company) should be 1/8" smaller than the actual opening on each side or 1/4" smaller in total.
The window trim must be 1/2" or greater on each side. This will allow any slight gaps between the foam tape used when applying tempered glass to the decorative panel to be covered by the trim.
David Gomm started building stained glass windows professionally back in 1983 and has become an expert at many aspects of stained glass building, design and repair. He writes a monthly newsletter at his better stained glass website.