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Andrea

Reinforcing Stained Glass Panels

How do I reinforce a panel? Can I use copper wire?

Copper is a soft ductile metal and has little strength. It has less strength than solder by itself, so a copper wire will do little to reinforce a panel.

Traditional reinforcement used what is called "rebar". There are two forms of rebar. One is a copper pipe, 1/2" to 3/4" in diameter. The circular structure of the pipe is strong enough to hold a panel flat. The ends of the pipe were set into holes in the frame. Copper wires were soldered to the lead joints in the panel, and when the panel was placed in the frame, the copper wires were twisted around the copper pipe. The other form of rebar is a zinc coated steel bar, 1/8" thick, and 3/8" to 1/2" wide. It is placed across the back of the panel on edge and soldered to the lead joints it crosses. The horizontal shadow lines you see in old church windows at 12" to 18" intervals used one of these types of rebar. It is still widely used. 

Recent technology has brought us two new innovations in reinforcement. One is a copper braid that can be integrated into the joints in foiled work. The braid is made from very fine, braided, tin coated copper wires. Now I said earlier that copper wire added no strength. That is true for just a single copper wire of some diameter. But the braid wicks up solder and becomes very stiff when filled with solder. The combination produces a strip that is stronger than solder alone. It would take a metallurgist to explain why this is so, but it works. That is all I know.

The other new innovation is reinforcement strip, commonly called "ReStrip", which is Venture Tape's trademark name. It is a thin, about 1/64" thick, copper coated steel band about 3/32" wide. You will also find restrip by other manufacturer's names: Morton calls theirs "strong line", Running Rabbit calls theirs "cameliner", etc. It is all the same stuff. In the thin dimension it is very flimsy and can be easily bent to follow contours across your panel. It is used between joints in foiled projects, and can also be used in lead came channels, placed against the heart before glass is inserted. Restrip is very rigid across its wide dimension.

There are other options as well. Cascade Metals makes a brass reinforced lead came. To quote from the catalog: "A unique product - excellent where strength is a must. This lead came has a strip of thick brass embedded through the heart of the came. This brass strip is surrounded on both sides by lead to protect the glass piece. This provides the user with flexibility to bend the came around even the tightest curves, yet has the strength of a panel that has been reinforced with rebar. And the came can be cut using regular lead nippers or dikes, no special saws are necessary." The price is twice that of lead came of the same dimensions. 

There are brass and zinc crowned lead cames available. They are made by forming a thin sheath of the metal over the lead came. Obviously, they will be much stiffer than lead came alone. Their appearance will be different than lead, and when mixed with lead came in a panel, patinas are used in an attempt to give a uniform appearance with varying degrees of success in the short term, and little success in the long term. 

There is also zinc came. It is not really zinc, but zinc coated steel. Zinc by itself is a soft ductile metal with little strength beyond lead or copper. Steel is what provides the strength. But solder will not bond to steel. Zinc will bond to steel and solder will bond to zinc. That is why the combination is used. Zinc came comes in two styles, inner bars and outer bars. Inner bars are formed in the traditional “H” shape and are used for reinforcement within a panel. Outer bars are shaped like a rectangle with a “U” channel on one edge and are used around the perimeter of a panel. 

And finally, there is “hard” lead. It is actually a lead alloy with 4% antimony added. While it cannot be substituted for true reinforcement, it can add strength to a panel on the borderline of requiring reinforcement.

If you are working with building codes that require triple glazing with tempered glass for safety reasons, you may not need to reinforce the panel at all. The tempered glass sandwich in itself may be sufficient structural support against bowing of the panel over the ages. In this type of sandwich construction, there is no place for the core stained glass layer to go; it is completely supported.

Restrip, copper braid, and reinforced came provide a reinforcement method that
is hidden within the lead lines of the panel, and eliminates the shadow lines of traditional rebar.

All forms of reinforcement are designed to prevent bowing and sagging in stained glass panels. The forces of nature must be dealt with in large panels. 12 perimeter feet or 6 square feet in panel size is the general guideline to consider reinforcement.

How is reinforcement applied?

Whatever type of reinforcement you choose, reinforced lead came, restrip, or traditional rebar, it must be one continuous strip from one side of the panel to the other to be effective. Remember, the purpose of reinforcement is to prevent sagging and bowing in the middle of the panel. To support the middle, reinforcement must extend into the frame on each side. But no one said it had to be straight or perfectly horizontal!

The Old School puts rebar straight across on the outside of the panel, attached where it crosses lead lines. The only rule is to try to avoid cutting faces in half. Centuries of application have conditioned our eyes to be comfortable with the horizontal shadow lines. Old School is structurally sound, we accept it visually, so there is nothing wrong in using this method. 

The Nouveau Old School still attached the rebar on the outside of the panel, but bent it to follow lead lines across the panel. I think this originally developed in the late 19th, early 20th century when jewels and overlays (plating) came into use, severely complicating the use of reinforcement because of varying thickness in the panel. I have seen early 20th century work where rebar was bent around jewels in one section of a panel and laid straight across other sections. I have also seen mid-20th century works where the rebar was bent to follow lead lines in an obvious attempt to diminish or hide the shadow lines. In one Art Deco piece the rebar followed a curve from the lower left side down to the bottom near the center of the panel. Two pieces of rebar were soldered to this near the center of the curve and followed curved lead lines up and across to the mid- and lower right side of the panel. Thus, there was not a continuous rebar across the lower third of the panel, which was approximately 6 feet in width, and 8 feet in height. But this 80 year old or so panel was flawless. There was no structural degradation. So I would have to say that this artist who broke the rules and abandoned tradition was successful. 

Now into the 21st century we have new technology: reinforced lead came, restrip, brass crowned lead came, and zinc came. And the "rules" for the New School haven't been written. We get to do that by experimenting and learning what works well and what doesn't. We can create reinforced works with or without shadow lines. We have much more freedom in our designs. What an exciting time to be a 
glass artist. 

When should I consider reinforcement?

The time to consider any need for reinforcement is in the design phase, before you start construction. Trying to add reinforcement during construction of the panel is certainly better than several years after installation when a failure has occurred, but it is like trying to add nuts to the brownie mix after the pan is already baking in the oven. Your options are severely limited at that stage of development. If you think about it during design, all of the reinforcement methods are available for consideration, assembly will go smoothly, and your work will be enjoyed for generations. So when should you start thinking about it?

Any window panel larger than 6 square feet in area, or having 12 perimeter feet is going to require reinforcement as a general guideline. Plan on it! As some artists have learned the hard way, zinc came around the perimeter is not necessarily the answer in and of itself. While it provides excellent support around the perimeter, it does nothing for the center of the panel, which is the area most vulnerable to structural failure. If the panel is installed in a frame, the frame itself provides all of the perimeter support a panel needs, and the use of zinc border came becomes an expensive redundancy. In the case of unframed hanging panels, the use of zinc border came is quite useful, and should definitely be considered. But how the came is attached to the panel is also very important to structural integrity. Unless there is sufficient attachment of the zinc border came to the panel, the whole panel can sag within the zinc border, pull away, and fall out. It has happened. 

Any door panel larger that 4 square feet in area, or having 8 perimeter feet will require reinforcement to maybe and hopefully hold it together when the door slams shut. The door jamb will stop the motion of the door, but what is going to stop the weight of all that lead and glass from continuing right on out onto the porch, when the door frame comes to a sudden stop? Think about it and design accordingly! (There is a lot of money to be made in the repair business, precisely because 
reinforcement is not considered in the design phase.) 

Is one type of reinforcement better than another?

In large panels we deal with several enemies. We have vibration from noise and traffic that tends to shake things loose over the decades. We have the environment to deal with: solar expansion & contraction of mismatched coefficient-of-expansion materials (lead expands and moves more than glass, which is different than cement, and is different than the frame), freeze - thaw cycles that tend to pry things apart, and the buffeting of wind, rain, & hail, that exert bowing forces on the center of the panel. Then we have the physical force of gravity, the terrific weight of glass, and the softness of lead. 

Without reinforcement, cement bonds break down, the panel bows, and gravity pulls it apart. Depending on a lot of factors, this process can take anywhere between a few years, and a few centuries. It is a deliberate process, and it cannot be stopped. It can only be slowed. Good design, good materials, good construction, and good installation will make your panels last centuries before they need repair. 

Zinc came borders have become the recent rage. I've recently read some articles that suggest that the life of zinc came in the environment is 1/10 that of lead came. Oxides, sulfides, and nitrides in the air, dust, and rain attack zinc came more aggressively than lead came. Properly mounted in a frame, the frame will provide all the edge support a panel needs. Central support of the panel is the critical element of an installed panel. Zinc came does help in handling the panel before installation with its added stiffness along the edges, but that is only a few hours of handling, versus decades of installed life. Remember that zinc came is really zinc-coated steel. What happens when the zinc plating is corroded away? RUST! You might want to think about the legacy you will leave. 

Reinforced lead came can be bent to follow the lines of your design from one edge to the other. This may require several right-angle bends to work your way around intersecting pieces. Reinforced lead came has a brass strip embedded in the lead heart. Where you need to make a right angle bend, you will have to nip the lead face of the came with your nippers. Nip the outside bend face with a single straight cut. Nip out a triangle on the inside bend face, so that when bent, the inside face will close, and the outside face will have a "square" hole in it. You will have to nip both top and bottom faces the came. DO NOT CUT THE BRASS STRIP IN THE HEART. It has to be continuous to reinforce the panel. You can nip the intersecting lead came to partially fill the square hole on the outside bend face of the reinforced came, and use a simple butt joint on the other side. When soldered, this joint will have a normal appearance to all other lead joints. 

You will have to measure carefully, and use your pliers to make the right angle bends in the reinforced came. If your glass is cut to a tight fit, you may have to nibble, or grind the corner of the glass piece to accommodate the bend radius of the reinforced heart. Fear not! With patience, care, and diligence it will work.

Is rebar superior to reinforced lead came or restrip? From what is known today, the answer is no. But then, we have a few centuries of experience with rebar, and only a few years experience with the new stuff. Laboratory tests indicate that the new stuff is just as effective as rebar. While lab tests try their best to simulate the actual environment, they rarely do. Only time will truly answer the question. And you and I will be long gone before that question is answered. Look at the zinc came issue. It has taken nearly a century (80 - 85 years to be more accurate) to discover that it does not seem to hold up as well as lead. But then again, the zinc plating processes of 80 years ago are pitiful by today's standards. Today's zinc coated steel came may well last a lot longer. In another 100 to 200 years we will know for sure. 

So I guess you shouldn't worry too much about this stuff. Use what has worked for centuries. Reinforcement has to be continuous from one edge to the other to be effective. Then use whatever material and method you choose. It's probably as good a guess as anybody's. And if you're really a worrywart, we know that rebar works and has several centuries of aesthetic acceptance. That's always a good fallback position. 

 

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