Strong Frames for Stained Glass Panels

Metals

Zinc is a popular material for framing copper foiled or leaded glass panels.  It is stronger than lead – up to eight times.  It gives a feeling solidity to the edges of the panel. 

However, it does have some disadvantages.  It is difficult to patina evenly and obtain the same colour as patinaed solder.  It resistance to progressive corrosion is weaker than lead. It requires special tools to fit around curves, making it best for rectangular panels.  It does need a saw to cut evenly, but so do a lot of the stronger metals.  A look at other options is worthwhile.

The strongest option is stainless steel.  This is difficult to cut and has special welding requirements, so is only useful in large and high corrosion installations.

Mild steel is widely available and cheap.  In certain circumstances – mainly small, thin profiles – it can be soldered.  The most secure joining is done with welding.  This requires equipment that stained-glass workers do not usually have.  However, there are a large number of metal workers that can to the work for you.

Brass is more expensive than mild steel.  It is an alloy of copper and tin and so can be soldered with the tools we normally use.  It is about half the strength of stainless steel, but three times the strength of zinc.  The tin content leads to a better patina result than zinc.

Copper is up to twice the strength of zinc, but the price fluctuates more than zinc.  It can be soldered. It requires different patina solutions than used for solder.

Aluminium is the same strength as zinc, but requires different joining methods as aluminium welding is a specialist activity.  Still, it will work on rectangular items with screws at overlapping joints.

More information on the relative strengths of various metals is given in a post on metal strengths.

Strengthening lead came

Lead is weaker than lead but can be bent to conform to curves and indentations for irregular perimeters.  If copper wire is incorporated and attached to the foiled glass, the soldering of the lead came to the joints at the intersections of the solder lines and the coper/came combination will provide greater strength than the zinc alone. 

When wanting to strengthen the perimeter of rectangular or shaped perimeter leaded panels, you can use 10mm “H” lead came soldered as usual to the whole piece as an alternative to soldering the wire to the panel.  Run the copper wire in the open edge of the “H”.  Pull the wire tight at the bottom and sweat solder at each corner.  Run the wire to the top on each side, where you can make a loop for attaching hanging wires and sweat solder the wires there too.  Then close the two leaves of the lead with a fid until they come together forming a single straight line.  If you want, a “U” or “C” edging came can be soldred to the outer edge of the "H" came to cover the line created by folding the leaves.

This post gives more detail about the process of incorporating copper into the perimeter of a leaded panel.

Lead free Solder

There are some problems to overcome when using lead free solders. 

One is that all, except for expensive compositions, lead-free solders have a higher melting temperature than tin/lead compositions.  The table in this link shows the melting temperatures.

Most lead-free solders have a wide pasty range, so careful attention needs to be paid when selecting the composition, if you want a eutectic, or nearly so, solder.

Some eutectic solders are:

65% tin, 25% silver with a eutectic temperature of 233C.  It is known as “Alloy J” and patented by Motorolla.

99.3% tin, 0.7% copper has a eutectic temperature of 227C. It is expensive.

96.5% tin, 3.5% silver has a eutectic temperature of 221C.  This is slightly lower than the tin/copper composition but more expensive.  It is also likely to rob copper from the soldering bit, although it is easier to solder with as it has excellent wetting properties.

Lower eutectic temperature solders are available:

91% tin, 9% zinc has a eutectic temperature of 199C.  It corrodes easily and has a high level of dross.  This makes it a poor choice for copper foil work.

42% tin, 58% bismuth has a low eutectic temperature of 138C.  It is a well-established solder, but it is expensive.

48% tin, 52% indium has the lowest eutectic temperature of 118C, but it is very expensive.

Copper bearing solders

Another problem is that a solder without lead, robs copper from the soldering bit/tip, and even more so at the higher temperatures lead-free solders normally require.  One means of avoiding the rapid deterioration of the soldering bit is to use solder with a small amount of copper included in the composition. As little as 0.5% can be useful.  Normally, nothing greater than 1% is required to extend the life of the soldering bit.

Eutectic copper bearing solder

However, only one of the commonly available solders is eutectic. This is 99.3% tin and 0.7% copper with a melting temperature of 227C.

Copper bearing solders and pasty ranges

Other copper bearing solders are available. Most of them have high temperatures and wide pasty ranges making them less useful for copper foil work.

  

Near eutectic solders

97.25% tin, 2% Silver, 0.75% copper has a small pasty range of 217C – 219C, making it a nearly eutectic solder and suitable for copper foil, except for its high melting temperature.

91.8% tin, 3.2% Silver, 0.5% copper has a pasty range of 217 – 218C, also making it a near eutectic solder suitable for copper foil; again, except for its high melting temperature.  With its high silver content, the solder is expensive.

95.5% tin, 3.8% silver, 0.7% copper has a pasty range of 217-220C.  This also has a small pasty range, but may be similar in cost to the 91.8% tin composition.

95.5% tin, 4% silver, 0.5% copper has a pasty range of 217 – 225C.

95.5% tin, 4% silver, 1% copper has a smaller pasty range of 217 – 220C, but may be more expensive.

Other copper bearing solders 

94.6% tin, 4.7% silver, 1.7% copper has a wide pasty range of 217 – 244C.

96.2% tin, 2.5% silver, 0.8% copper, 0.5% antimony has a

smaller pasty range of 217 – 225C and may be slightly cheaper because of the reduced silver content.

  

95.5% tin, 4% Copper, 0.5% Silver has a pasty range of 217 – 350C and is the usual lead-free plumbing solder.  The high melting temperature of 350C makes it unsuitable for most copper foil applications.

97% tin, 0.2% silver, 2% copper, 0.8% antimony has a high melting temperature and wide pasty range of 287 – 318C., which makes it unsuitable for copper foil.  It is known as “Aquabond”. 

95.5% tin, 4% silver, 0.5% copper has a pasty range of 217 – 225C.

95.5% tin, 4% silver, 1% copper has a smaller pasty range of 217 – 220C, but may be more expensive.

94.6% tin, 4.7% silver, 1.7% copper has a wide pasty range of 217 – 244C.

96.2% tin, 2.5% silver, 0.8% copper, 0.5% antimony has a

smaller pasty range of 217 – 225C and may be slightly cheaper because of the reduced silver content.

Lower temperature copper bearing solders

94.25% tin, 2% silver, 3% bismuth, 0.75% copper has a pasty range of 205 – 217 which is smaller than many of the other copper bearing solders.

90.7% tin, 3.5% silver, 5% bismuth, 0.7% copper, with a pasty range of 198 – 213C, has a lower melting point than many other copper bearing solders.

93.4% tin, 2% silver, 4% bismuth, 0.5% copper, 0.1% germanium has a relatively small pasty range of 202 – 217C, but because of the incorporation of rare earth metals may be expensive.