Annealing Thickness

Factors relating to how to determine an annealing soak time and cool rate are numerous. The thicker the piece, the more conservative you need to be in the soaking and cooling. This is because the annealing soak time increases almost exponentially with the thickness of the piece. The reduction in the speed of the anneal cooling has an approximate exponential relationship also – requiring much slower rates of cooling.

In the simple case you use the smallest dimension to determine the thickness for annealing. The heat is assumed to travel the shortest distance to dissipate. Thus a piece cooled from both sides will be taken as the simple case. This needs to be modified in a number of circumstances.

1 - Pieces cooled from one side, as where the shelf is heat retentive, or fired on the base of the kiln can effectively cool from only one side. This doubles the distance the heat has to travel. So you need to use the numbers from any annealing table for glass twice the thickness of the actual piece.

2 - Then if you have variations in the thickness of the piece, you need to be more careful, because the thinner areas will cool faster than the thicker, giving the potential for stress creation.

3 - If you are doing anything less than a full fuse, you will need to be more careful. If the pieces are tack fused, they will in part, act independently of each other and so need more careful, slower annealing.

4 - The less symmetrical a piece is, the greater care needs to be taken, just as with differences in thickness.

5 - The heavier or more insulating the refractory materials that surround the piece, the greater the care needed in annealing.

A rule of thumb is to consider these variables and add to the soak times and reduce the speeds of anneal cooling in accordance with the number of variables exhibited in your piece. With the first of these variables - cooling from one side - use the schedule for twice the actual thickness of the piece. Then add another step up in thickness for each additional variable.

So, as an example, the most common complicating factor is the inability of the kiln to cool the pieces equally from both sides. This requires you to double the thickness to read an appropriate schedule from the table making the schedule for 12mm glass.

But your piece of glass also varies in thickness, so you need to add another step up in thickness, giving you 19mm.

However you are not intending to go to a full fuse, so you need to add another thickness. Now you are up to the table for 25mm.

But the pieces are asymmetrical, so another step up in thickness is required giving you 38mm.

And you have heavy dams under and around the piece, so yet another thickness level is required to read an annealing schedule from the table. This gets you up to 50mm as the part of the table you should be reading from. So you will need an 8 hour soak rather than 1 hour and need to reduce the temperature at 4C/hour rather than 80C/hour.

Of course, not every project has all these variables in it, so you use only those that apply, but each of those that do apply requires a step up in thickness to read the schedules for the numbers to plug into your controller.

This is a rule of thumb, so you will need to test any pieces for stress and learn from your experience if this is conservative enough for you pieces.

Copper Backings

“Is it possible to to fuse copper to the back of glass?

The easy answer is - no.

But it can be done. There are a number of conditions that will help.

The copper needs to be thin and flat. It works best if you clean the copper of any oxidisation, 
and then coat it with borax or other devitrification spray that can act as a glass flux.

The fusing has to be done with a long soak to ensure the bottom of the glass is as soft as the top to assist the attachment of the copper. The devitrification solution will help soften the glass next to the copper sheet. You also have to protect your shelf from contamination by the copper sheet. This can be done by using 3mm fibre paper under the copper.

Not all attempts will be successful, showing that this process is on the edge of acceptability.

It is easier simply to glue the copper to the back.

“Does it matter whether it has been fused already?”

The glass does not have to be fused prior to attempting to attach the copper to the back. If it has been fused, you need to run a slower schedule than when fusing glass for the first time. A schedule for slumping, but with a higher target temperature – at least fire polishing – will be required.

Ramp Speeds for Slumps and Drapes

I find that a steady slow heat up gives best results for both slumping and draping. Many do a two stage heat up with a slower initial rise to a temparature above the annealing point and then faster afterwards.

A slow steady increase in temperature allows all the glass to be nearly the same temperature both across the piece and from top to bottom.

Speed in draping, especially where there are different colours and thickness, promotes "wings" as any unevenness in the heat across the piece will translate into variable drape speeds. Allow all the glass to get to the same heat, by going slowly.

I proceed at the same speed from start to the forming temperature - no speed up at all. Yes, the glass will accept it a rapid heating to the target temperature, but it does not promote even slumps or drapes.

Candle Bridge Moulds

A candle bridge mould is one of the most difficult moulds to use successfully. The problems relate to the kinds of work you are trying to do, the size of the glass to put onto the mould, the shape of the piece and the stability of the resulting piece.

With a candle bridge you are trying to do a combination of slumping and draping at the same time. You are slumping into the middle and draping over the curved sides.

Additionally the candle mould requires the glass to fall into a small opening and this requires long soak times. Long soak times mean the glass that is draping stretches while the central portion is trying to fall into the opening. Of course, if you don't want the depression to be flat, you don't have to soak so long and the stretching effects on the draping part of the of the glass won't be so great.

It would seem logical to measure the mould around the drapery curve (or arc of the mould) and to the shape of the ends, but experience has shown me that this leads to glass that is too long along the sides and bent at the ends. So I cut my blanks for candle moulds as a rectangle without curved ends and then round the corners of the rectangle just a little by nipping them with my grozing pliers before fusing.

If you measure along the top and along the length of the mould you have a piece of glass that will be increasing in length at the draping part of the mould, meaning that it will fall off the curve and onto the draft (or side) of the mould. The draft is an angle from the vertical. Good moulds are made with a draft so that if glass were to fall over the edge it still will be possible to get the glass off the mould.

The draft on a mould means the diameter of a circular one is greater at the base than it is at the rim. And it is common to measure only the diameter at the rim.  In the same way the dimensions at the outside base of a rectangular mould are larger than the rim of the mould.

Back to the rectangular candle mould. The draft on this means that measuring the base of the mould is slightly wider than the curved part of the mould, but less than if measured around its curved portion.

Experience has shown that in the case of the candle moulds measuring the width of the mould is sufficient. There is enough height in the moulds I have used that it does not make any functional difference if the glass does not reach the bottom of the curve on the mould. It is better than hanging off the edge.

The length of the glass should be no longer than the shortest part of the mould's length. Cutting a curve into the glass to allow a small overhang produces a depressed lip because of the length of the soak required for the slump into the small aperture of the candle depressions.

My soak for candle moulds is 90 minutes at my process temperature. This gives me a flat depressed area for the candle to sit, but it also means that the draping glass has been stretching. And it also means that the glass will drape unevenly as the various colours absorb heat differently allowing some parts of the glass to stretch more than others.

The placing of the glass on the mould is absolutely critical. It must be exactly parallel to the sides of the mould. Any slight movement from that will induce a twist in the resulting piece allowing it to rock. Arranging it exactly right and placing some kiln washed furniture at each side to keep it in place until it begins to slump is an important aid.  
The glass will begin to bend before it sticks to the kiln furniture.

I have never been able to get a stable candle mould whether from 3mm or 6mm thick glass. I always have to grind the base a little to make a stable piece. I take it as part of the process, but careful placing reduces the work.

Cutting Box Hinges

Cutting the brass tubing for box hinges is best done with a saw.

The manual version is to use a fine toothed saw - similar to those used by jewelers – with very light pressure.

The power solution is to use a Dremel or similar hobby motor with a cutting wheel attached. This cuts through the tube cleanly and quickly.

In both cases, a fine rat's tail file can clean up any burrs within the tubing.

If you use the internal tubing you can cut both at the same time. However, it is quick and easy to use the appropriate sized copper wire to insert and then bend down onto the corner of the box. This gives greater flexibility and avoids waste.

Vase Cap Fitting

“Can anyone offer me any tips for fitting the brass caps onto lampshades?”

There are at least three ways to get the right vase cap size.

Make up your shade in a cardboard mock-up. Use 3mm thick card or foam board to represent the glass, as the thickness of the glass is important in determining which vase cap is the correct size. Try your vase cap against the cardboard model, then if you need, alter the pattern so the glass pieces meet at just the right place to make the lip of the vase cap fit just over the top of the glass. You can do this by either shortening or lengthening the pattern a little at the top edge.

The second also involves making a cardboard mock up. After making this maquette, choose a vase cap that overlaps the top opening, covering all the edges. 

The third option is to use two vase caps, one above and one below the opening to clamp them together trapping the edges of glass between them. Use a furling and lock nuts with no solder at all to hold the lampshade together.

A general discussion of panel lamp dimensions

Squaring Panels

When building leaded glass panels to be placed in existing wooden frames, you need to make sure the panel is as square as the opening in the frame. The first requirement is to make sure your cartoon is squared, or has right angles at each corner.

I use a “roofing iron” as it is called in the UK. It is a steel tool about 600mm on one side and 400mm on the other. Its original use was to work out the pitch of roofs and check the same pitch was maintained all along the building. The first important thing – now that all roof trusses seem to be prefabricated – is that they still are in production. The second thing is that they all have a fixed right angle.

Using this roofing iron will ensure your corners on the cartoon are right angles. This helps in the drawing of the cartoon as you only need set the iron on the base line and draw the verticals without having to measure the width higher up the cartoon. Of course you should check that the width is still correct at the top, just in case there has been a slip.

Then you have to stick to the cartoon.

When you are setting the battens to ensure the sides are held where you want them while you continue with the leading, the roofing iron again will ensure that you have placed the battens at right angles. You choose which line is to be your base, and nail or screw it into place. Ensure it is exactly parallel to your cut line and then align one side of the iron against it. Place the other batten snugly along the length of the other leg of the iron and you know you have a right angle.

When you are completed leading, but before soldering you can check on the accuracy of the angles by using the roofing iron again at each corner to check on the “squareness” of the whole panel. If the panel is out of square, you can tap on the battens not yet nailed/screwed in place to ease it all back into “square”

Vase Caps

Attaching the vase cap securely is important as often the whole lampshade hangs from the attachment points between the cap and the solder seams of the shade.

Once you have assembled the shade and tack soldered it together, perch the vase cap on the top covering the opening and apply solder so it joins the vase cap with the solder seams. It is a good practice to turn the lampshade over and apply solder from the seam to the inside of the vase cap. A good strong joint at each seam will be perfectly strong enough to hold the shade in position for many years.

Another another method of attaching vase caps will be given soon.

Tinning vase caps

Sieves, Gauges and Grits

The commonly used designation for grits has become the gauge This is a confusing measure as it increases in number as the size of the material decreases in size. This is because the number of wires per unit increases with decreasing size and the gauge refers to the number of wires used to sieve the material.

In an attempt to indicate the actual sizes of material refered to by the gauge sizes, I have used part of a standard table of equivalents.

12 gauge is 1.7mm or .0661inch

14 gauge is 1.4mm or .0555inch

16 gauge is 1.18mm or .0469inch

18 gauge is 1mm or .0394inch

20 gauge is .85mm or .0331inch

25 gauge is .71mm or .0278inch

30 gauge is .6mm or .0234inch

35 gauge is .5mm or .0197inch

40 gauge is .425mm or .0165inch

45 gauge is .355mm or .0139inch

50 gauge is .3mm or .0117inch

60 gauge is .25mm or .0098inch

70 gauge is .212mm or .0083inch

80 gauge is .18mm or .007inch

100 gauge is .15mm or .0059inch

120 gauge is .125mm or .0049inch

140 gauge is .106mm or .0041inch

170 gauge is .09mm or .0035inch

200 gauge is .075mm or .00295inch

230 gauge is .063mm or .0025inch

270 gauge is .053mm or .0021inch

325 gauge is .045mm or .0017inch

400 gauge is .038mm or .0015inch

450 gauge is .032mm or .0012inch

500 gauge is .025mm or .001inch

635 gauge is .02mm or .0008inch

Soldering techniques

My experience leads me to say that the tip of the iron should be in contact with the surface of the material being soldered. If the metal is not hot, it will not take the solder well. In the case of copper foil, the metal is so thin it will heat up almost instantaneously. The solder should be added to the heated metal to obtain a good joint. All the advice to hover just above the surface and allow the molten solder to heat the metal below seems to make for hard work suspending the iron, and for possible cold joints.

The principle is that both metals should be hot for a good join. In leaded work you can sweat a joint and get as good (and in some way a more lasting) joint as by having a bead. That is because by adding the minimum of solder (sweating) you will have to get the base metal hot for the thin layer of solder to flow. I feel that many people do not understand the principles of soldering, but look only to the finish. It is possible to have a beautiful joint, or bead and have the joining of the metals technically weak.