Metal Framing Materials

Lead is a very weak metal. Therefore various other metals are often considered for the perimeter of the panel to strengthen the whole.

Zinc is a metal often used for strengthening the perimeter of panels. It is stronger than lead – by about 8 times. It is relatively easy to solder. However it is subject to more rapid corrosion than lead.

So an alternative is aluminium which is about about the same strength as zinc. However it does not accept soldering, so professional joining or cold fixing solutions are required to make the frame.

Copper is over 10 times the strength of lead and can be considered as an alternative to zinc. It accepts solder well, but as a came is extremely expensive. It does corrode to a verdigris unless protected and maintained. However, because of its strength, copper wire - as a single strand or several twisted - can be used inside other came such as lead or zinc to provide strong support.

Brass is about 19 times stronger than lead. It is available in came profile as well as “U” and “L” profiles. It accepts solder well and resists corrosion. It is more expensive than lead, but similar in price to zinc.

Mild steel strength varies but is at least 27 times stronger than lead. It does not accept solder easily, and does corrode without painted protection, but is a less expensive option than aluminium, zinc or copper. As an angle or “T” shape, mild steel and iron have been used for centuries to support leaded glass panels.

Stainless steel is at least 37 times stronger than lead. It is difficult to weld and does not accept solder at all. It is very resistant to corrosion.

When considering framing solutions for panels, the main factors to consider are relative strength, corrosion, and joining methods possible.

Brass, Copper, Lead and Zinc all can be joined by solder. Aluminium and stainless steel cannot be joined with solder. Although mild steel can be joined with solder, a good strong joint is difficult.

The stronger the metal, the thinner profile required, which can make metals that are more expensive by weight an economical solution, as metal prices are most often by weight rather than shape.

It also is possible to combine a stronger metal with a weaker metal, such as including copper wire or steel rods in the lead came.

It is not absolutely necessary to solder the panel to the framing material. A frame can be made and the panel fixed within it by other than hot soldering methods. In this case the frame takes the whole weight of the panel.

Metal Strengths

Metal Strengths

The strength of metals is most often compared by their tensile strengths. These numbers are Newtons per square millimetre and represent the relative strength of each metal compared to another.  The range of numbers indicates the variations caused by various alloys.

Tin                      19

Lead                14 – 32

Solder 60/40        48
Zinc                120 – 246

Aluminium       120 – 246

Copper            220 – 270

Brass              340 – 540

Mild steel         500 – 750

Stainless steel  740 – 970

These figures may be of interest in considering what frame to place around a free hanging stained glass panel.

Panel Framing Options

Some framing options for free hanging stained glass panels are given here.  They are not exhaustive, of course, but do give some principles to be considered when making frames.  Wood and metal are the two traditional materials for framing panels to be hung.

Wood

A wood frame requires joints of some kind. These joints are important to the durability of the frame. The two main kinds of joints are glued and screwed.

Glued joints

Lap joints seem to be strongest. An odd element relating to the strength of this joint is that placing a wooden pin in the joint weakens, rather strengthens the lap joint.

Mortice and tenon is also a strong joint. It requires considerable skill to make a good joint.

A mitred is among the weakest, but can be strengthened with a biscuit or fillet in the joint.

A mitred joint with biscuit ready for glueing.

Screwed joints

These have a lot of movement before failure, but do give a lot of resilience to the joint as they can stretch rather than immediately give way. They also can be used with any of the glued joints if appearance is not of prime importance.

Frame style

The width and thickness of the frame are interrelated – thicker frames (front to back) can be narrower, thinner frames need to be wider. So the desired appearance of the frame width has a significant effect on the dimensions of the frame.

Metal cames or angle

Lead can be an adequate framing material, but if strengthening is required, you can use copper wire within the came and fold the leaves closed over it. You can also use steel rod within the came, as shown in the posting.

Zinc is a stronger metal than lead – about 8 times, but still has a weak tensile strength. I corrodes easily, but accepts solder as a joining method. It is more expensive than lead.

Some of the variety of zinc came available

Aluminium is a little stronger than zinc, but does not take solder. It has similar costs to zinc.

Some of the aluminium profiles available

Copper is about 1/3 stronger than zinc and also takes solder. It corrodes to a verdigris, but can be protected by clear varnish or paint. It is more expensive than zinc, but can be used as wire which is less expensive than other forms of copper.

Brass is over two times stronger than zinc and also takes solder. It resists corrosion well, and is a little cheaper than copper.

Some of the brass came options.

Mild steel is over 3 times stronger than zinc, but does not take solder at all well. It is relatively cheap and welds easily, making it a good framing material, although a method of fixing the panel into the frame is required.

Stainless steel is about 4.5 times stronger than zinc, but does not take solder and needs special welding. It resists corrosion very well, but is expensive in relation to zinc.

Hanging and fixing options

Two point hangings are the most common as they prevent twisting and distribute the weight to the sides of the panel.

The hanging material is straight up from the zinc framed sides to the fixing points

The hanging material whether line, wires or chains should be straight up from the sides to two separate fixing points. A triangle shaped hanging puts a bowing stress on the panel or frame.

A variation where the chain is taken to the corner of the window, is less secure, as it stresses the joint away from the sides

Loops or holes for screws should be placed in the frame rather than the panel.

The hanging is from reinforced corners directly to fixing points on the overhead beam

Ensure the fixing points for the hanging wires are sound and secure.

If the panel is fitted tight to the opening, consider ventilation requirements to reduce condensation between the primary glazing and the hung panel.