Wire in glass

 

The cracks around the wire imbedded in the glass in the above image are not incompatibility cracks. They do not surround the square piece that traps the wire into the glass. These are from differential expansion/contraction stress between the wire and the glass. 

 

Picture credit: Charmaine Maw

This picture shows the stress that a single strand of wire will induce in glass (the bright light around the wire).  Wire is never going to have similar characteristics to the glass, so the glass must be strong enough to contain the resulting stress.  Anything that increases the mass of the wire, such as twisting or spirals, will increase the stress. 

 

Kanthal and nichrome wires are best as included wire hangers. They are designed for high temperature work and so do not weaken from the heat. This means that high temperature wire as thin as 0.5mm/22 gauge can hold a lot of weight.  Much greater weight than is used in most glass objects to be hung rather than fixed.

Keep the wire as a single strand and as thin as possible, consistent with sufficient strength.  Hammering wire flat can also help reduce the stress by thinning it.

Profile

A sharp tacked piece needs to be fired as though thicker. This example is a single layer base and a square of glass to trap the wire fired to a sharp tack.  It needs to be fired as though 2.5 times the thickest part - 15mm.  A rounded tack fuse of the same layup would need to be fired as for 12mm.

Layup

The use of wire in glass needs to consider how the air will escape from around the wire.  Yes, if the wire exits the glass, there is a channel for it to dissipate.  But air tends to collect along the length of the wire.  If the wire is fully enclosed in the glass, the layup must accommodate the need for air escape routes.  This might be with a fine layer of powder, design elements, chips of glass to hold the outer edges of the glass up for longer, or other devices.

 

Scheduling

The example shown at the start of this blog, is a sharp tack and needed the 2.5 times scheduling.  That probably would have avoided the crack in the single layer base.  That single layer cools faster than the wire with the added piece of glass.  A bubble squeeze is a good idea, even though it would not normally be considered.  This gives the best chance of reducing the bubbles that form around the inclusion.

 

You need to be careful about increasing the ramp rate until the glass has passed out of the brittle phase.  This is about 540˚C/1005˚F. The increase in the ramp rate during the brittle phase may cause cracks. It is, of course, more likely to occur during cooling because the metal will be contracting more than the glass during the brittle phase.  This contrast in contraction rates induces stress that may be great enough to crack or break the glass.

 

 

Wire for Fusing

Although there are other ways to combine wire with glass, one popular method involves fusing wire inside the glass. This technique generally fuses and seals the wire between two layers of glass, so it is important to select a wire with the right characteristics. The main characteristics are:

1. The wire must be capable of withstanding the heat of the kiln.

2. The wire must emerge from the kiln in a relatively pristine condition, or at least can be easily cleaned.

3. The wire must also retain the desired flexibility and pliability. If it's too soft or brittle it may not support the piece.

4. The wire must not react with or contaminate the glass. In most cases colour changes and metal flakes are not desirable.

5. The wire must be of a small enough diameter to avoid causing excessive stress within the glass.

6. It is a bonus if the wire is reasonably priced or even inexpensive.

This post gives the characteristics of some types of wire for fusing. 

Types of Wire for Fusing

Having mentioned the characteristics needed of the wires for inclusion, this is a description of the good and bad points of some common wires used as inclusions within glass.

Nichrome (nickel chromium) is a generally favoured wire, due to it easy workability, ability to hold up in the kiln and maintain its strength afterwards. It does turn dull after firing, but can be cleaned up with a brass wire brush.

Copper is a softer wire to use, and exposed parts tend to be weakened. It may tarnish or change colour. Some twisted/braided copper can work better than single strand copper, but test first.

Sterling silver will work, but tends to scale and needs to be cleaned after firing. It can react with the glass and change colour. It tends to be soft after firing.

Fine (pure) silver works better than sterling, but even more prone to react with the glass - turning yellow. Some glasses (French vanilla and certain reds) will also change colour when exposed to silver.

Stainless steel is very stiff and hard to work with, but can be fused if desired. It retains its strength and if of the appropriate grade requires only treatment with a brass wire brush.

Gold or platinum wires will work, but are very expensive.

High Temperature Wire for Screen Melts

You can use high temperature wire for screen melts. This is variously described as Kanthal or nichrome wire.  It is the same kind of wire used in the heating elements of your kiln.

wire with bent ends

To use the wire, you lay or weave the wire and support it on both ends.  Weaving the wire provides more support, but is not necessary, as the wire is strong enough to support a lot of glass.

first line of wires pushed into board

You need to have the wires as tight as the supporting material will allow. Straightening the wire before beginning to fix them will help, as will thicker wire.

The wires need support at each end, which can be brick, cut up shelves, or strips of tile.  If you do this, you can form a dam or vessel in which to put the glass without fear of it spreading over the edge.

I use fibre board for the support and just bend a right angle into each end of the wire to push into the board.  These can be arranged in any configuration, although for ease of illustration, I have used a rectangular arrangement of wires.

A grid of wires ready for kiln wash

Put the completed screen over a tray or sheet of plastic to collect the excess kiln wash.  Mix the kiln wash very thick and pour over the wires. I put the board with wires into the kiln to heat to about 200°C to help the wash stick.  I repeat a few times.

Make sure you coat the area surrounding the screen to avoid the glass sticking to the supports.

When the kiln wash has dried, knock off the stalactites of wash on the underside of the wire to prevent any excess kiln wash being incorporated into the final piece.

Place on kiln washed supports, and put the glass on top of the screen.

This is a relatively quick and inexpensive means of providing a custom shaped screen.  

One disadvantage of this over stainless steel rods, is that it is difficult to get enough kiln wash to stick to the wires to be able to pull them out easily.

Firing wire inclusions

Wire and other metal inclusions often cause bubbles to occur around them.  The standard solutions are to add frit to the corners, or powder or fine frit around the inclusions.   You can also flatten the wire or metal to reduce it height. These most often work well.  Sometimes though they don’t eliminate big bubbles around the metals.

In this case think about firing upside down. This is not the whole piece; it is only the inclusion and the bottom layer of glass.  Place the wire or other inclusion on the prepared shelf. It will be most successful if placed on 1mm or thicker fibre paper to allow any trapped air to escape through the fibre.  Place the base glass on top and take to a tack fuse with a bubble squeeze included.  You might even want to consider cutting the base larger than the final piece to be able to cut off the thickened edges and make a more successful piece at the end.

After tack fusing upside down, the inclusion will be imbedded in the glass with an almost flat surface and little in the way of air pockets at the edges.  Clean very well, especially any spalling from the metal and of course, clean the glass thoroughly.  Cap and fuse with a bubble squeeze again.  The bubbles around the inclusion should be minimal if not eliminated.

This method will allow the glass to sink around the glass making a much flatter piece for the capped full fuse. It should also make for a flatter finished piece with many fewer bubbles.

Hangers for Sun Catchers

Unless you are using some manufactured system or a frame, the most frequent way to provide hanging points for copper foiled sun catchers is to create a loop from copper wire.

Hangers should originate in a solder bead that goes some way into the piece. The loop's tail should lie a significant distance into the solder line to ensure it does not pull the piece apart. If this is to remain invisible, some planning will be required to allow the small extra space between the foiled glass.

The loops for hanging a piece of any size should not be soldered to the perimeter foil without reference to the solder bead lines within the piece, as the adhesive and foil are insufficient to hold the weight without tearing.

Reinforcement of free hanging or projecting elements can be done by placing wire around the piece with a significant excess going along the perimeter in both directions. The supporting wire can go into the solder line, if it is a continuation of an edge of the free hanging piece.

An example of a piece that needs reinforcement around the wings to keep them firmly attached to the body

The strongest method of proving hangers is to wrap the wire around the whole perimeter of the piece. Choose easily bent copper wire. This will be pretty fine, but when soldered, will be strong enough support the whole piece.

The perimeter wire can also be concealed by edge cames

The hanger can be made by leaving a loop of wire free along the perimeter. This way you can hang from any convenient place on the perimeter. This loop can be made by a single 180 degree twist in the wire, or by bending a loop into the perimeter wire. In all cases you will need to tin the wire to blend it with the rest of the piece.

An example of wire running between the yellow and purple on the left and incorporated into the design

This perimeter wire can be simply butted at the start/finish of the wire. It could be overlapped, but this is unnecessary on any piece where this method is adequate for support. The start can be at the top or bottom, although I prefer the top, so the wire is continuous from loop to loop. The reason for continuing beyond the loops is to provide support to all the edges of the sun catcher.

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.

Wire for Hanging

The most common wires used for inclusion in fused objects are copper, brass, nickel/chrome, stainless steel and sterling silver.

The strength of the wires – strongest to weakest - seem to be in the order of stainless steel, nickel/chrome alloy, brass, silver, copper. The metal you choose will be related to the weight of the piece, the available thickness of wire, and aesthetics.

All of these are subject to fire scale or fire stain, a blackened surface on the wire. This can be removed by abrasive cleaning of the exposed metal. The metal within the glass most often takes up the fire scale too. This can be reduced by thorough cleaning of the metal before enclosing it in the glass. Coating the metal with a flux such as borax often reduces the incidence of the fire scale too.

The techniques of cleaning the fire scale from the metal range from scrubbing and polishing to tumbling. The tumbling has the advantage of hardening the softer metals such as copper, and silver.

Copper looses much of its strength in the firing, and often needs gentle working to stiffen it. This is where tumbling is so useful.

Pure silver normally leaves a yellow stain on the glass. Sterling silver - an alloy of copper and silver – is less inclined to do this. However the exposed wire will stain the shelf and any subsequent glass unless well supported by 1 mm or more of fibre paper.

It is common in silversmithing to pickle silver to remove the fire scale after any heat work.