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.

Residues

Sometimes a white residue appears alongside the solder bead sometime after a piece is finished, covered in patina, and waxed. This seems to have two causes.

First - Residual acid

As there is a possibility of some acid remaining on the piece, rinse with a bit of bicarbonate of soda added to the water. This will neutralise the acids from the flux and patina that may still be lurking under the foil and solder beads. If you get a frothing while cleaning with the soda, you will know there is still acid present. Wash - rather than scrub - those areas again with the water and soda solution until there is no foaming.

Second - Trapped moisture

Moisture can also produce this as it allows minerals to migrate from under the solder seams. The advice seems to centre on cleaning. First do not use much soap in the initial cleaning solution. After rinsing ensure the piece is completely dry by setting it aside in a warm dry place for a day or two before waxing or sealing.

Those that use paste waxes seem to have less difficulty than those who use thin or spray on waxes. The heavier waxes seem to seal any moisture within the structure. The moisture seems to be able to migrate through the thinner waxes. It is not optimum to have moisture sealed within the panel, as it will eventually come through the wax as it ages.

So it seems the best long term result will be achieved by ensuring everything is absolutely acid free and completely dry before waxing.

Scoring Glass

Cutting glass is done by “scoring” the surface of the glass with a glass cutter, then breaking it along the score line. The break you make will always follow the path of least resistance, so you want to be sure that the score you make becomes that easy path and glass breaks the way you want it to.

Holding the Cutter
Generally, you use the cutter by moving it away from you, so you can see the cartoon lines as you score. When using a straight edge such as a cork-backed ruler to guide your cutter, you can pull the cutter toward you, or push it away as suits you. The cutter should always be held at a 90 degree angle (left to right). You can determine this by looking down the cutter to the wheel and to the cartoon line below.

It is important that the work be done from the forearm rather than the fingers or the wrist. The forearm should be held closely to the body. This reduces the freedom of movement, giving clean flowing score lines. It also reduces the actions that can lead to repetitive stress injuries. Any turning required by tight curves can be done by turning the body from the hips or shuffling around the bench with the glass at a corner.  Of course, for long cuts your arm will have to extend from you body in a parallel direction with the score line.

Scoring Pressure
The second and very important element in scoring glass is the amount of pressure used.  Very little pressure is required.  You should hear no more than a quiet hiss on transparent glass and almost no sound on opalescent glass.  However some manufacturer's transparent glass has almost no sound either.  So the important element is the pressure, not the sound.   Most people start with applying far too much pressure. Tests have shown that only about 2 kg of pressure is required for a clean score.

You can test the effect of this amount of pressure on a bathroom scale.  Place a piece of clear glass on the scale and without touching the glass with your other hand, score it noticing how much weight is being recorded.  Keep trying until you are at the 2 kg area of pressure.  Try breaking the glass.  Score a curve with the original amount of pressure and break the glass.  Then using the same curve score the glass with the 2 kg pressure and break the glass.  You will see and feel the lesser pressure provides a clean break.

Excessive pressure leads to breaks showing significant stress marks on the edge of the glass.  Too little pressure has no effect on the glass, making it impossible to break along the score line.  The correct pressure (ca. 2 kg.) leads to almost vertical stresses being put into the glass which assists the breaking along the score line.  Too heavy pressure creates stress marks which are at increasingly large angles with the increasing pressure.  This will still break cleanly on straight lines, but when working around curves the glass can follow one of the lateral stress marks away from the score line.  Excessive pressure is often the cause of glass breaking away from the score line on a curve, especially a tight one.

Foiling Nuggets

Grinding of the edges of the nuggets is not required for foiling. Roughing up the surface helps some adhesives hold better, but it depends on the viscosity of the adhesive and the degree of "roughness" of the surface. The adhesive on copper foil sticks better to a smooth than a rough surface. Try sticking it both to glass and to fine sandpaper and see which is easier to scrape off, for example. You will find the foil easily comes off the sandpaper, which is the texture of the surface you leave when grinding.

So you do not need to grind. You may need to wash them with soap and water to remove any oil that may be on the surface to ensure a good contact, however. Just put the foil on the clean nuggets. Then put a bunch of the foiled nuggets in a plastic container and shake around until all the nuggets are nicely burnished.

Check each one to ensure they are fully burnished to the nugget. Smooth any lifted parts of the foil with a fid and they are ready for soldering.

Glass Stuck to Moulds

Glass that is stuck to moulds needs more care in removal than removal of glass from kiln shelves does.

The major element in removal is to get the mould to release the glass. This requires some diagnosis of why the glass is stuck.

• Is the glass trapping the mould? This happens most often when the glass is draped, especially over ceramic moulds.
• Has the glass been fired high enough to fuse to the mould? If you have fired the glass to tack fusing temperatures, you may find more occasions when the glass sticks slightly or firmly to the mould.
• Is the mould trapping the glass? This can happen when slumping into a steep sided steel mould. Occasionally a steep sided ceramic mould will show the same effect.
• Has the separator been too thin or failed? If none of the previous elements apply, it may be that the separator was too thin or has been fired to tack fusing temperatures in a previous firing.

You can use mechanical methods to free the glass from the mould by inserting a thin pallet knife between the glass and the mould. This works better for items where the glass is inside the mould. If the glass is outside the mould, the chances are that you will break the glass. Using mechanical methods for any glass that is more than lightly stuck will most often lead to breakage of the glass, and often both items.

Where the mould is trapping the glass, you can put the item back into the kiln, but upside down and supported a centimetre or so above the kiln shelf. Heat the glass gently toward slumping temperatures. The glass should fall from the mould at 300 or 400C, but you need to keep watch to make sure you do not over heat the glass.

Where the glass is trapping the mould and you are using mechanical methods, you normally need to decide which is more important – the mould or the glass. It is just possible to break a ceramic mould and leave the glass, if the glass is 6mm or more. If the mould is more indestructible, you will probably lose the glass.

With ceramic moulds you can try heating the two to 300C or 400C and reach in with appropriate protection to try to lift the mould out of the glass. If the mould is steel, it will expand faster than the glass and break it.

Once you have the glass off, you may need to repair the mould.

Aperture Drops Finishing

After the piece has cooled and been removed from its ring, you can consider how to finish the piece.  The first decision is whether to retain or remove the rim from the vessel. In some cases, the rim can be retained as an integral part of the piece and there is little work needed to finish the piece.  Possibly only tidying up the edge of the rim and cleaning the bottom.

Removing the rim

But for most aperture drops and for most people, it is desirable to remove the rim. To have successful drops without rims, you most often need to have access to cutting and polishing equipment.  There are several ways to do this. 

The method that uses least equipment is to score around the upside down drop just above the rim.  When scored, tap the rim with a soft hammer to release it.  This is not always an even break and sometimes runs into the length of the drop.

A low tech way of cutting is to put a diamond cutting blade on a Dremel-like battery powered tool and with a flow of water grind through the side of the drop.  It is best to have a small flow of water directed at the cutting area, rather than immersing the rim in a bath of water.  This helps avoid electrical shock.

The rim can be cut off in portions with a tile saw, cutting quarters, eighths, sixteenths off the rim, approaching the edge of the drop.  Those with adjustable height wet saws can cut through small portions at a time of the rim, and support both the rim and the drop, especially when nearing the completion of the cuts.

There are also specialised versions of the wet angle grinder that make cutting of the rim easy and much more certain of a good result.

Finishing

After any of these methods of removing the rim, the drop edge, and possibly bottom, needs to be ground and polished.  Fire polishing is not possible as the drop would collapse long before the rim was smooth.

Because the rim will be relatively thin, it is possible to grind and polish with hand pads.  However, it is quicker to use a flat lap or linisher with a succession of finer grits to grind and polish an edge.  HIS Glassworks has a series of videos and this one gives good information on the methods and progression of grits to get to a polished edge whether by machine or by hand.

Aperture Drops Annealing

The soak at annealing temperature will need to long to accommodate the temperature variations within the thick and thin parts. The thin parts will be able to cool much faster than the thicker parts.

The objective in annealing is to keep all parts of the glass cooling within a 5C range, so the soak will need to accommodate those differences. I suggest a minimum soak time is 90 minutes for a 9mm thick blank, 2 hours for 12mm and 3 hours for a 15mm blank to be certain all the glass reaches the same temperature.

Annealing the drop has two main considerations – the variation in temperature over the length of the piece and the variation of thickness of the glass. These two in combination make it difficult to find a rapid annealing and cooling schedule. So having spent quite a bit of time so far on the piece, choosing a conservative schedule is sensible.

The variation in temperature between the top and bottom of the kiln can vary quite a bit, maybe as much as 20C for some kilns. So you can see immediately that the annealing will need to be slow if you are going to keep the thick and thin glass within 5C of each other. It would be possible to use schedules for annealing thick pieces just as they are published for the thickness of your blank, but it is more conservative to use a cooling schedule for the next size up to ensure a good anneal.

Thus, for a 9mm piece I would anneal at 55C/hr for the first 55C below annealing, then 99C/hr for then next 55C. After that you can go much faster. For a 12mm piece I would go at 25C/hr for the first 55C, 45C/hr for the next 55C and 150C/hr to room temperature. For a 15mm piece I would go at 15C/hr for the first 55C, 27C/hr for then next 55C, and 90/hr to room temperature.

It may be possible to go faster than this in annealing, but this is cautious to make sure the variations in both thickness and temperature are considered.

Aperture Drops - Stopping the Drop

Arresting the drop and cooling the piece can be complicated, as you need to cool the kiln quickly enough to stop the glass moving.

The higher the forming temperature of of the work, the quicker you need to stop the movement of the glass. This will involve opening the kiln to cool the glass enough so that it becomes stiff and resists further movement. You need to be aware that you are cooling glass that ranges in thickness from relatively thick to relatively thin. The thin parts will cool faster than the thick parts. Flash cooling for too long will make the thin parts very stiff, while the thicker part are still hot. This could lead to breakage if allowed to continue down to the annealing soak temperature.

A lower forming temperature will allow you to simply advance to the rapid cool portion of the schedule down to the annealing soak without the need for flash cooling. You do need to make this skip to the next segment just a minute or so before the piece reaches its desired length or shape. This will not be difficult to judge as you will have been checking frequently at this portion of the firing.