Light Boxes

Description and Use

Light boxes are in many ways development from the glass easel. The glass easel was used in studios to wax up the painted glass and display it as it would be seen in a window. Sometimes the glass painters painted across all the glass at once, so this method enabled them to see the results immediately.

Nowadays people tend to use back lighting for these and other purposes, so the light box has become more popular. Some of the uses are outlined here:

The light box is very useful when tracing or altering designs. The back lighting enables you to use other paper than tracing papers to transfer the design elements. You can fold the paper along the lines of symmetry to check on how the lines match, or to copy the lines from one side onto the other side at the designing and cartoon stages.

The light box can help select glass colours either initially or when the main pieces have already been established. The combination of the glass over light shows how they interact with each other. At later stages when the main glass is cut, it can help avoid unwanted bright or dull areas.

Possibly the most common use is in cutting dark or opalescent glass. The additional light allows you to see the cartoon through the glass and so cut directly from the cartoon. This can be enhanced by blanking out the excess light from around the glass or cartoon.

The light box enables the arrangement of the cut glass pieces to be assembled to view the colour balance and have a virtual view of how the panel or window will look as a finished piece. An additional step toward the result is gained if each piece is outlined in white-board markers – use black pens - to represent the lead or copper foil and their widths. This stops the light between the pieces from causing you pupils to contract, and gives a more accurate representation of the appearance of the final pane.  White-board markers can just be wiped off the glass without using spirits.

The light box is important in painting. The back lighting shows the effect of the painted line or level of shading immediately. This allows adjustments to be made quickly and accurately before firing,

Depending on how the light box is built, it also can be used as display lighting. This can be as up-lighting or backlighting.

Requirements

The top surface needs to be firm and scratch resistant. Toughened or laminated glass is good for this. The larger area covered, the thicker the glass needs to be, or there needs to be support under the glass to avoid breakage from pressure. The toughened or laminated glass resists breaking from dropping material onto the light box.

You need to have daylight corrected light sources for you light box, especially if you are doing any glass selection on it. Fluorescent tubes are easily available, but other light sources can be used. You need to have ventilation to allow the heat generated by the lights to disperse. Fluorescent tubes do not generate much heat and so are the common choice for lighting.

You need diffused, even light across the whole surface. This requires a diffuser and there are a number of solutions. You can sandblast the back of the top sheet, but I find this does not provide enough dispersion. You can sandblast both sides, which gives better dispersion of the light, but is difficult to clean and so needs another sheet on top. The best dispersion of light comes from using a sheet of opaque acrylic with about 80% light reduction. The difficulty with this is that it is flexible and needs support if any glass cutting is going to be done on the surface. I place the acrylic sheet underneath a sheet of 6.4mm laminated glass. This gives both solidity and dispersion.

Light is a central consideration in building the light box. The intensity is controlled by two things mainly – The number of lumens and the intervals of the light sources. The best way toward even light distribution even with good dispersion sheets, is to have multiple light sources. It would be possible to pack the box with light fixtures, but this is expensive and generates a lot of heat. It also may make the light too intense to be comfortable to work with. In general, fluorescent tubes placed at about 150mm centers apart will provide all the light you will need.

To make sure you get all the benefit of the light you need to build an enclosed box with ventilation holes or slots that is painted matt white on the inside. This allows the light to be reflected upwards through the surface without bright spots that can be caused with gloss paint.

You need to consider the size of the box in terms of surface area. This will relate to the space you have available and the scale that you work at. In addition to a separate surface the box can be an area of the work bench, or covered by a separate work board – whether permanent or temporary.

The height of the box will need to be considered. Will you be sitting or standing while working at the light box? It needs to be high enough in either case for you to maintain a straight back.

You need to consider the ability to screen parts of the light so the light is directed only at the work area. Large areas of light will overwhelm the glass, making it appear darker than the finished piece will actually be.

You need to think about the amount of flexibility your box requires. If you want to use it as part of your display equipment, it needs to be mobile and relatively light. This will interact with the materials to be used in construction.

Construction

Light boxes can be constructed in a variety of ways. The simplest to construct is the free standing, horizontal, single purpose light box.

You need to consider the size of the box in terms of surface area. This will relate to the space you have available and the scale that you work at. Having determined the surface area required or possible, you need to think about the height. The top should be of a height so you can stand or sit with a straight back while drawing, cutting or painting. This will vary according to your height and whether you will be standing or sitting. Typically these heights will be the heights of the benches and desks you already use, but you need to check again that you are actually working with a straight back, as this will reduce the fatigue you might otherwise experience.

Note that if the box is going to be sat at, it will need to be narrower to be able to reach to the opposite side. If you will be standing at the box, it can be at least half again as wide as the sitting version. A sitting version will also affect the depth of the box containing the lights. It may not be possible to have anything deeper than 100mm. This will produce some problems with the evenness of the light, but nothing that will make it unusable.

Then you need to consider the depth of the box. In principle, the deeper the box the better diffusion of the light. But there are limits. If the box is really deep, more lights will be required, and potential storage space is lost. I recommend about 150mm for the depth of the box. I then place the fluorescent tubes at 150mm centres across the box. It does not matter which direction they are oriented. That will be more determined by the available fittings and the dimensions chosen.

The flexibility you have in building your own box includes a number of things which could be constructed separately or in combination.

You can cover the light box with a sturdy work board to do all kinds of work on top. So this makes a combination light box and work bench. This top can be hinged so you don't have to lift it off each time you want to use the bench. It should have some support mechanism so it does not fall on your or your work. I have used a chain that allows the board to go back just beyond the vertical. These chains can sometimes get in the way of your work.

In addition to a separate surface the box can be an area of the work bench. The important element is that the rest of the surface of the bench should be at the same level as the light box top. Any variation runs the risk of breaking the glass you may be working on. The cover for this can be hinged to protect the surface when the light is not needed.

Often you will be working on pieces smaller than the illuminated area. It is possible to arrange things so that each light fitting can be turned on and off independently to allow light reduction or intensification as you need. It is simpler to have sheets of opaque card to place around your work area to reduce the extraneous light that will overwhelm the glass that you are selecting or painting, for example. In the case of too much light the glass or the painted lines and shading look darker than they really are as a result of your pupils contracting against the light.

You could add a variation to allow the light box to be used as a near vertical illuminated glass easel. This requires a set of hinges, a ledge on the hinged side and a support of some kind at the back, similar to a piano lid support. This is most useful in painting and in waxing up the pieces to view the whole panel before leading or foiling.

You need to think about the amount of flexibility you require the box to have when considering the materials to be used. If you want to use it as part of your display equipment, it needs to be mobile and so relatively light. This will interact with the materials to be used in construction. In this case you may want to make greater use of metals for their strength in relation to weight. 

 You probably will use opaque acrylic sheet as the surface. If you do, you will need to give it internal support to keep it from bowing. The best for this is another piece of acrylic – clear this time – glued to the top sheet and to the bottom of the box between the light fittings.

Working surface

I recommend your top should be 6.4 laminated or 4mm toughened glass for anything up to 610 by 1000mm. If it is larger, you should go to 6mm toughened, as 8.6mm laminated glass is pretty expensive. I suggest glass because it is strong, rigid, scratch resistant and easy to clean.

You can use a router to form a ledge for the glass to sit on. You can use a less machine intensive method, by nailing thin battens or quarter rounds around the glass. But the structure which confines the glass should be no higher than the glass surface. If it is higher than the glass, you can simply plane or sand it down. Insure there is no part of the fixings of the glass higher than the glass surface. This is especially important when cutting glass on the light box. If the surround is higher, you run the risk of breaking glass that is for one reason or another overhanging the edge. It also makes it easier to get the glass on and off the light box.

To get the appropriate diffusion you need to do more than sandblast the underside of the glass. While this will provide some diffusion, it is not enough. You can put another sheet of glass, sandblasted on both sides, underneath the top sandblasted sheet to provide good dispersion of the light. However, I have found a 3 or 4 mm sheet of white acrylic that is 70% -80% opaque provides the best diffusion of the light elements, even though it is more expensive than glass.

You also need to have a method to be able to get at the lights. This can be by having a removable section of the boundary. You can also make use of the ventilation holes, if appropriately placed, to lift the glass. A portion of the box sides can hinge to allow access to the lights through the side, although this is more awkward than fitting from above.

Lighting

Light is a central consideration in building the light box. 

The best way toward even light distribution even with good diffusion sheets, is to have multiple light sources. I recommend placing them at the same distance apart as the depth of the box. It would be possible to pack the box with light fixtures, but this is expensive and generates a lot of heat. It also may make the light too intense to be comfortable to work with. If you can control the general lighting of your studio and you can turn it off or down, you will not need such intense lighting in your box.

An alternative, but more complicated method is to build the light box with baffles so the light is never directly under your work. Commonly, this would require the box to be built wider than the glass upon which you will be working. The light reflects from the sides and bottom of the box to give an even light. In this case, the single sandblasted surface would be sufficient to disperse the light and keep your eye focused near the surface of the glass or cartoon on which you are working.

You need to have daylight corrected light sources for you light box, especially if you are doing any glass selection on it. Fluorescent tubes are easily available, but other light sources can be used if they can be found in daylight colours. Fluorescent tubes do not generate much heat and are available in daylight corrected colours. So these are the common choice.

You still need to have ventilation to allow the heat to disperse, though. Ventilation can be provided in a number of ways ranging from drilling holes in the sides, to providing a slot in the side or bottom.

You need to have access to the light fittings to replace bulbs. It is easiest if this is by removing the glass top. You can provide tabs on or under the glass to lift it with, but these often interfere with other uses. You can use the ventilation holes if they are high on the box to stick a lifter under the glass to be able to grasp the edge. You can have a removable section to the beading that holds the glass top in place. You can provide a couple of finger holes at the top edge of the box to enable more direct lifting of the glass without disturbing any of the box fittings.

Another important element in getting the maximum amount of light out of your box is to paint the inside white. This should be a matte or at most silk finish. Any glossier finish will produce bright reflective areas. Shiny surfaces such as aluminium foil also produce these unwanted bright areas. In fact, a matte white surface gives more apparent light than aluminium foil in the light box.

The lights should be wired in series so they all come on at the same time. It is of course possible to have a switch for each fitting, to vary the intensity of the light for the work you are doing. This does add a bit to the expense, but may be valuable for your way of working.

Cutting Glass

Cutting Shapes

Outside Curves

Outside curves are usually the easiest curve to break out. You do not have to worry about breaking the piece, as the break - if it goes off the score line - will be away from the piece rather than into it. Outside curves normally have complimentary inside curves. So on the principle of making the most difficult break first and the easiest last, the outside curve will be broken out last. Unless, of course, there is a straight line on the other side of the curve when that would be the last, as it is the most straightforward cut.

Deepest concave curve taken out

Curve on right that has both concave and convex curves is taken out second

Score started from both ends and finally tapped out

Simple curve on the left taken out

Finally the almost straight line is cut and removed

Cutting Circles

Fixing the suction cup at an appropriate place on the glass sheet

Start score at limit of movement of arm

Hold the cutter nob firmly and rotate until you hear the click of the wheel meeting the start of the score

First, score the circle, making sure that you start and stop the score line at the same point. Circles can be scored freehand or with a circle cutter.  This example shows the use of a circle cutter with a graduated arm.

Looking closely shows the scored circle

Turn the glass over - the scored line shows more clearly

On a firm, but not hard surface begin to run the score by pressing over the score  with your thumbs

Turn the glass over onto a piece of corrugated cardboard, or other surface with some give, with the score line face down. With your thumbs, press along the score line until you see the score line "run" progressively and completely around the circle. This prevents the relief scores you are going to make from running through the circle.

Continue running the score completely around the circle

Turn glass back to scored side and mate relieving scores at right angles to the run score

Turn the glass back over to the side on which you scored it. Score several lines perpendicular to the circle to the corners of the piece of glass. Gently open these scores by tapping with the ball of your cutter, or with your hands, pliers, or other tools.

Tap the relieving scores to run them to the circle

Break the pieces away from the circle without tapping it to give a cleanly cut piece of glass

 The the pieces should fall cleanly from the circle leaving you with no rough or jagged edges.

Cutting Circles from Opalescent Glass

Score as normal.

Be careful about putting too much pressure when scoring as, in general, opalescent glass does not make as much sound when being scored as transparent glasses do.

The difficulty with opalescent glass is seeing where the score is when you turn the glass over.

If you are using a piece of glass not much larger than the circle you are cutting, you can place the fingers of your hand over the score line and your thumb on the back as you lift the glass to turn it over. This gives you the location to begin the pressure to run the score. As the first part of the score runs, you will be able to follow the leading edge of the opening score around the circle.

Positioning the Circle Cutter

If you have a suction cup on the circle cutter, it will be easier to hold in place. But a three legged circle cutter is possible to keep in place too.

In both cases, one hand holds down the centre and the other operates the cutter. Make a test circle with no pressure to ensure before you start that you know the cutting bar will not bump into anything else on the bench. This also ensures that you have the circle to be cut placed appropriately on the glass.

To make the score start with the bar under your supporting arm and swing around to the other side of your arm until you hear the click or scratch indicating that you have come back to the start.

Cutting Small Diameter Circles

It is possible to cut regular, small diameter circles without buying a lens cutter. It can be done with the assistance of a Lazy Susan or cake decorating turntable.

Cake decorating turntable with circle inscribed

Draw the circle of appropriate diameter on the turntable with a compass. Place the glass on top of the turntable, and position your cutter above the drawn circle. Press on the cutter with one hand and turn the glass with the other.

Glass scored and tapped to run the score 

Steady your hand with the cutter by keeping your elbow tight against your side. This enables you to make a very good, if not perfect, circle without buying an expensive small circle cutter.

Relieving scores tapped oug
t

You will not be able to run the score by turning the glass upside down and pressing as you can with larger circles. You will need to make a number of relieving cuts to the tangent of the circle and break them away one by one. Yes, this does leave a rough edge at various places around the circle, so grozing or grinding will be necessary.

Excess glass  removed

Circle removed.  Note very sharp shard at 10 o'clock which along with other irregularities need to be grozed or ground off

If the glass is too dark or opalescent to see the line, make a template and put it onto the glass. Cut beside the template or use the template to mark the glass. Then place the marked glass on to the turntable and cut as with transparent glass.

Cutting ovals

Cartoon with oval placed on turntable ready for scoring

 This example uses a small oval, but the same process can be used for large ovals too.

Scored and run with one relieving score placed

When scoring large ovals, the same procedure as for glass circles can be used.  Simply turn the glass over and run the score with your thumbs as for the circle.  No tapping will be necessary.

Small oval broken out from the glass

Cutting concave curves

There are several methods that can be used to break out extreme inside curves. In all the cases you should retain a significant amount of glass around the edges of the curve. You should make this most difficult cut the first on the piece. If it fails, you may be able to move the glass a little and score again, without loosing too much glass.

Glass scored along the concave line on the right

Relieving scores made and the first piece taken out

Further crescents of glass taken out

Next to last crescent taken out

Last crescent taken out in several pieces

To accomplish inside cuts by using the hand breaking method and/or pliers method, you must first score according to the cartoon line. Then you can make a series of concentric scores. Gently run the primary score line so any break does not run beyond this. Remove the graduated concentric scores in sequence.

You can also accomplish this type of cut by using the criss-cross pattern of score lines instead of concentric scores. First you must run the score of the curve to avoid the criss-cross lines from running beyond the curve. Then you begin to take out the little pieces from the waste area.

Another method is to score and run the curve, and then score a number of small crescents in the waste area, looking like fish scales or the fan type of paving seen in some European cities. Pull out each small crescent working toward the main curve.

Deep inside cuts can be assisted by using a lazy susan – a turntable affair, similar to a cake decorating turntable.

The first question you have to ask yourself is whether you should make such deep inside cuts or redesign the piece to avoid creating such fragile shapes.

OK. You have decided to go ahead with your plan in spite of good advice. Put your cartoon onto the turntable and the glass over it. If the glass is too dark or opalescent, make a template and mark the glass. Adjust the starting point, put one hand on the glass and cartoon, and turn the glass instead of yourself to get round the score with ease.

Then you can begin the task of breaking out the glass from the score line as described above.

Cutting thin strips

Cutting thin strips of glass such as used in Mission Style patterns and precision fusing projects requires skill and persistance. For transparent and translucent glass you can arrange a right angle guide on a board and tape a piece of lined notepaper to the jig. Use a cutting square and move it right along the lines on the note paper making four or six scores at a time and then breaking on the last score first and then every other score, and then each one in half.

Another method is to use the edge of the bench as a guide. With a small adjustable carpenter’s square, you hammer in nails at the predetermined width (plus half the thickness of the cutter head). Align the glass to the edge of the bench between the nails. Place a straight edge against the nails and score. This gives strips of the same width every time, but works best with strips of 10mm (3/8”) or more. This is illustrated in the processes section. 

The thinner the strips are to be cut, the more important it is to make the scores and then divide the scored sheet in half - the two halves in half each - the 4 quarters in to halves, etc, until you are down to the piece that only needs to be divided in two.

Breaking Apart the Last Two Thin Strips

For multiple thin strips of even widths, score all the strips first. Then break all the scored strips off the remaining sheet as one piece. Start the breaking process by breaking the scored sheet in the middle, then in the middle again, until there are only two to break apart.

Strips scored and broken from main sheet

Breaking pairs off the scored sheet

Cut running pliers are most useful until the last two thin strips are to be divided.

At that point use two breaking pliers to hold each side of the two pieces of glass. The noses of the pliers should almost touch on either side of the score line. Apply pressure in a downward pivoting motion to break the pieces apart.

Breaking Tapering Pieces

Breaking thin pieces of glass can be tricky, but there are a few things you can do to help direct the break the way you want it to go.

Tapering piece scored

Broken from main sheet

Relieving scores made alongside curved and tapering pieces make the breaking more certain. A relieving score is one that is in addition to the primary score. This additional score will allow you to break the thin or tapering piece from the larger sheet safely, and then go on to break out the delicate piece.

Relieving score broken away

The object is to always be breaking away less glass than is retained. The use of two breaking/grozing pliers, one on each side of the narrow pieces gives more even pressure than fingers or cut running pliers with wide jaws.

Score run started from narrow end

Running score from blunt end

Completed break

Rehearsing Special Cuts

It is important to remember the basic tips as they become even more important with difficult cuts:

• Keep an even/constant speed during the scoring
• Make sure the cutter is vertical – eye the cutter from top to wheel to cut line
• Stand behind the direction of the cut line
• Use your body to turn, do not use wrist or arm

For difficult cuts you can increase your confidence by rehearsing the score with a feather light movement of the cutter on the glass along the score line. Make any adjustments to the placing of the glass or yourself shown to be necessary by this rehearsal before beginning the score.

Start with the most difficult score first. Any break-outs or mistakes will not waste much work or glass.

Break out each score as you make it. You can store up trouble by making multiple scores before starting to break. The score lines can run across the main piece when breaking off the scored glass. Any inaccuracies will also be magnified by making all the scores before breaking.

Cutting Bottles

Cutting bottles seems to have a fascination for many people. There seem to be three methods – thermal shock, scoring, sawing.

There are various ways to apply thermal shock to assist with breaking the bottles.

- A string tied around the bottle and soaked in a flammable liquid is a common way to apply heat. As soon as the flame has gone out, you immerse the bottle in cold water; the temperature differential should crack the glass where the string was.

- Filling the bottle with water to the level where the break is wanted and then applying gentle heat with a torch flame at that level should promote a crack.

- Alternatively, the bottle can be scored and put into the freezer for a while and then into hot water.

Scoring is the common method to start a crack.

- This is followed by tapping from inside the bottle with tools from a purchased kit or home-made tappers – a metal ball on the end of a curved piece of metal.

- The score line can also be the preliminary step in the application of heat or cold.

These provide the cleanest edges to the cuts. However there is quite a high failure rate using these methods.

Sawing is method that provides a higher success rate, but is wet, and leaves rough edges to the cut, requiring further cold work.

- Band saws designed for glass can be used, but usually do not have a high enough throat to allow the thickness of the bottle to pass through.

- Most tile saws cut from underneath, so rotating the bottle can lead to a cut completely around. This requires a lot of skill to do free hand, so you need a jig to keep the bottle at right angles to the blade and the bottom the same distance from the blade while rotating the bottle all the way around.

Cutting Flashed Glass

Some recommend cutting flashed glass on the clear or non-flashed side. This is based on the idea that the flash is only laminated to the main body of glass. My view is that flashed glass has proved to be very stable over many centuries, and so is firmly a part of the whole sheet.

What is more important is to observe that flashed glass often has a bow. If you place the glass on the bench, you may find that it rocks or sits up from the bench. If you cut the glass on the convex side, that is the side which is not resting on the bench except at the edges, you may find that you break the glass during the scoring, unless you are using the lightest of pressures. It is more certain to get a good break if you score the glass on the concave side - that is where the edges are slightly raised from the bench. So the important element in deciding which side to cut is to score the concave side whether that has the flashed colour or not.

This does not occur with all flashed glasses, and is more important on large sheets than small ones. On the small ones, the curvature is so small as to be immaterial.

Preventing Chipping When Using a Tile Saw to Cut Glass

One of the most common problems in using a tile saw to cut glass is the tendency for the saw to chip the edge of the glass as it completes the cut. This occurs when the blade of the saw has less glass to cut through. Excessive and uneven pressure and the lack of support cause this break-out.

It's possible to improve the quality of the cut by slowing down and pushing the glass through the blade more gently, but this seldom solves the problem completely. Pushing equally on both sides of the cut is also important to minimise the break-out.

One solution that does work is to provide support for the end of the bar. This adopts a woodworking method for preventing splintering at the ends of cuts.

Use a scrap length of pattern bar or other thick glass. Place it against the glass being cut. As the blade emerges from the glass being cut, hold the two pieces firmly together and continue cutting. The blade should immediately engage the second piece of glass. Once the saw blade entirely clears the first piece, you can turn off the saw and remove a chip-free slice from the pattern bar.

You'll need to trim off the ends of the scrap piece from time to time, but you can use the scrap over and over until it becomes too small to do the job.

This works best with a tile saw where the blade is below the cutting surface. When you use an overhead saw, the breakout is much rarer.

Other Sections
Tools

Cutting Glass

Techniques and Safety

Use of the Glass Cutter 

When cutting glass your are first scoring the surface to weaken the glass and then second, breaking along the score line. The glass will always follow the path of least resistance. It is important to keep this in mind when “cutting” glass as it has significant implications for scoring and breaking.

Use the cutter by moving it away from you, so you can see the cartoon lines as you score. When using a straight edge, you can pull the cutter toward yourself or push it away, whichever suits you.

Grasp of the cutter

The classic or traditional grasp is for use with a pencil cutter. The cutter is placed between the first/index and second /ring fingers with the thumb at the back of the cutter. This initially is awkward. Its advantages are that it transfers most of the work to your arm rather than fingers and wrist, and it restricts the movement of your wrist, leading to smoother curves.

Basic cutter in traditional grasp

Oil filled pencil cutter in traditional grasp

The modified grasp is also for use with pencil cutter. The cutter is placed between the thumb and first/index finger. The second /ring finger is also most often used beside the first/index finger. The fingers should be straight to avoid excessive strain on the fingers and possible carpal tunnel problems later.

Modified grasp with straight fingers

The fist grip for use with pistol grip cutters. The cutter is held similar to a gun, with the first/index finger pointing down the shaft holding the cutter head. This pointing action seems to aid the accuracy of cutting. This applies to cutters with right angle handle attachments also.

The palm grasp is for the small Toyo and other palm cutters. The cutter is placed on the pad beneath the thumb and held with the first/index finger and thumb.

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.

Moving 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.

Alignment

The cutter should be held so that your dominant eye looks along the cutter to the cut line just in front of the wheel. This ensures you are looking directly to the line and that your cutter is not tilted to one side or the other. Looking down the side of the cutter only ensures that it is tilted with the effects indicated above.

Tilted Cutter Effects*

A tilted glass cutter has the effect of changing the angle of the cutter wheel. It narrows the angle on one side and increases it on the other side. So on the side tilted away from vertical (which is what happens when you look down the side of the cutter) has an sharper angle with the glass. This is likely to produce chips along the cutting line. The side which is tilted toward the glass has a more blunt or shallow angle with the glass. This produces high stress along the line.

The combination of these two effects make for a rough edge when broken and for break failures because of the stresses being at angles to the desired vertical fissure line.

Steering the Cutter

It is important that the work be done from the forearm rather than the fingers or the wrist. The elbow 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. Of course, for long cuts your arm will have to extend from you body in a parallel direction with the score line.

All these instructions about holding the cutter are reasonably straight forward when cutting straight lines, but become more difficult when applied to curves. The temptation is to use your wrist to make the curve. However this both tilts the cutter – giving the results described – and risks the cutter sliding across the glass.

You should attempt to be behind the cutter at all times. This means that the steering action should be from your body. Most times, turning your torso from the waist is sufficient to enable the cutter to follow the curve. On curves which are deep or go through more than 90 degrees, it is best to place the glass at a corner of the work bench and “walk” around the piece by both twisting at the waist and moving your feet around so that you can make a 270 degree cut without moving your forearm from your side.

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 4 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 consistently at the 4 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 4 kg pressure and break the glass. You will see and feel the lesser scoring 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. 4 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.

The pressure needs to be applied consistently throughout the length of the score. Uneven pressure leads to inconsistent breaks.

Scoring Opalescent Glass

Cutting opalescent glass often gives difficulties in getting clean breaks along the score line. You need to remember that the opals do not make much if any sound when cut with the correct pressure. If you are scoring so that you hear the ziiip sound, you probably are pressing too hard. When the score is too hard, the opals do not break easily or truly. Only the same pressure as used on transparents is required. Feel the pressure rather than listen for the sound.

Speed

The speed of the cutter needs to be consistent too. If the speed is not nearly constant, different pressures are transmitted to the glass. This also leads to inconsistent breaks.

Where to Start Cuttng the Glass

As a general rule, always make the hardest cut first. Glass tends to run in a straight line. This means inside curves should be done before any other cut is made. This avoids excessive wastage should the break come away from the score line.

Glass placed to make the inside cut at the right first

It will be most efficient to place the glass to be cut with the inside curve facing the raw edge of the glass. If something goes wrong, the glass can be moved and tried again, resulting in less glass and time wasted.

It is also hard to run very thin strips of glass without getting ragged, chipped edges. Allow a 6mm minimum distance from the edge of the glass when placing the glass on the cartoon unless the edge glass is going to be used for the whole edge of the cut piece.

Direct or Trace cutting

Place the glass over the pattern and run the cutter along the cartoon lines you see by looking through the glass. There's no need to draw lines on the glass. For translucent glass you may need a light box.

You should be aiming to cut glass efficiently and accurately. Trace cutting is the most efficient, as it completes in a single operation what other methods – such as drawing on the glass or making templates from the cartoon - take several steps to accomplish.

It is more accurate because each extra step required for other methods increases the possibility for error. The fewer times you copy the original pattern lines, the less likely you are to diverge from the original pattern.

It is very important to keep the cutter at right angles to the glass - as seen from side to side, not vertical. This of course is true of all cutting. It makes the cutting inaccurate, because the light is bent when coming through the glass much like water changes the apparent angle of sight into its depths. Tilted cutters also have undesirable effects when breaking the glass.

Cutting with Patterns or Templates

When scoring around a paper pattern it is necessary to steer (turn) the cutter in the proper direction. The paper will not turn the cutter for you. You should steer the cutter by turning your upper body rather than your fingers, wrist or elbow. Failing to do this may allow the cutter to run over the pattern and so fail to score the glass.

Alternatives to using the paper pattern directly as a guide in cutting glass are to outline the pattern paper on the glass with a pen or to draw the pattern on the glass while it overlays the drawing. You follow the inside edge of the pen line with the cutter. However this results in cutting glass much as when cutting directly over the cartoon and so merely introduces an additional step in cutting glass.

This shows a set of templates in use for repetitive cutting. The template is drawn around for subsequent cutting

Directly cutting the glass over the cartoon avoids the time spent in making patterns, and the difficulties and inaccuracies in multiple transfers of the shape. Often a light source is required under the cartoon to enable the lines to be seen through the glass. There will always be times when the glass is so dark or opalescent that the lines cannot be seen and therefore a pattern is required.

Keep the pattern cutting restricted to the times when nothing else will do. The only times I use patterns for cutting are when the glass is too dense for the cartoon lines to be seen through the glass with light behind or for repeat shapes where a pattern can speed the process.

I draw around the pattern pieces, as that avoids the possibility of the cutter riding up on the card that I use for templates. This comes from several occasions when the cutter did go over the template which prevented the score and so created a bad break. Others do score successfully around the template stuck to the glass.

Pattern Scissors Usage

The purpose of pattern shears/scissors is to cut out the space between pattern pieces equivalent to the came heart or the space needed for foil.

The scissors come in two thicknesses – one for leaded and the thinner for copper foil.



If you must use pattern scissors, use them in short cutting motions. Use only the first 50mm of the blades which are closest to the pivot point. Otherwise the paper jams in between the blades. It remains difficult to cut long straight lines without quickly having an “accordion” of paper blocking the cutting action.



Some suggestions to make things easier:


• Clean the blades regularly. If you are cutting anything with adhesives, clean the blades after each use with spirits.

• Often running a little soap along the blades helps to lubricate and smooth the action of the blades.

• Use stiff high quality paper so you do not catch fibres in the scissors. Waxed paper or stencil card are good materials to use.



Organising pattern pieces. 


You have made a second and third copy of the cartoon haven’t you?
 Now that you have a lot of pieces need to decide how to organise them

• Mark any grain direction before you cut the pieces apart.
• You need to code the pieces in some way. 
Numbering with reference to the main cartoon is most common. 

• It is a good idea to colour code the pieces and if the surface will take it, a shading of the colour makes a quick visual reference.

Keeping the pieces together
Envelopes are easy to write on for colours, or areas such as borders, background, etc.

• Freezer bags that are transparent and have a band to write on are very good, as you can see the pieces without opening the bag.
• You need a labelled bag or container to keep all the envelopes together.




Alternatives to pattern scissors


For copper foil, you can use normal scissors, by cutting to the inside of the pencil or inked line. You can also use a scalpel or craft knife to cut to the insides of the marked lines.


For leaded glass you can use a felt tip pen (a bullet point is almost exactly the right width when new). Cut with scissors or craft knife at the sides of the line.



Alternative to pattern pieces


Use the European or trace cutting method as described here.

Breaking glass with your fists 

For scores with significant, but not necessarily equal, amounts of glass on each side of the score this is a quick simple approach to breaking glass. After scoring, raise one edge of the glass and put your fingers under the glass on each side of the score. Curl you fingers into your palm, and put your thumbs on top of the glass. Turn your wrists outward while holding the glass firmly, and the glass will break cleanly.

With practice, the initial part of a curved score can be run by applying light pressure. Then you can turn the glass around and run the score from the other end to the opened score. This avoids lots of tapping and gives clean edges to the cut glass. It is just as simple as using cut running pliers and avoids the flare often associated with using cut running pliers.

This technique works best with glass that has at least 50 mm each side of the score and on gently curved lines. For tight curves and narrow strips other methods need to be used.

Breaking Pieces from Large Sheets  

Breaking a piece of glass from a large sheet is often a frightening prospect. It doesn't have to be. It is better to cut a straight line piece from your larger sheet than it is to try to cut a curve.

Use a cutting square or other non-slip straight edge to guide the cutter. You can push as in normal stained glass cutting, or you can draw the cutter toward you as glaziers do. In either case, the pressure needs to be even and the speed consistent.

When moving large scored sheets, avoid pulling the sheet by one end. The score may run suddenly and not always along the line. Instead, move the sheet with support on both sides of the score.

After the glass is scored, you have choices about how to run the score.

One easy way to break off large pieces is to move the sheet so the scored line is just inside the edge of the bench. The biggest piece will be on the bench and the smaller piece in your hands. Give a quick, sharp downward push with both hands on the overhanging glass. This action will separate the piece from the main sheet. Having the glass score inside the bench edge gives you a place for the broken off piece to rest, rather than pivoting toward the floor.

Or you can slide the straight edge under the glass on one side of the score, and press firmly, but not sharply on each side of the score. The glass will break evenly along the score line. This is a more gentle method of breaking the glass. A variation on this is to place a couple of matchsticks or glass painting brushes at each end of the score and apply the pressure.

If the glass sheet is of a size that you can hold it in both hands with the score between, you can draw it off the bench, let it hang vertically, and bring your knee up briskly to hit the score line, and it will break easily. This is a showman’s way of breaking glass sheets when the score line is approximately centred on the sheet.

Cut running pliers often do not work very well for long straight scores on large sheets of glass. However, if you use this method, tapping at the start and at the end the score line before squeezing the running pliers will help the score to run the way you intend. This is sometimes the only way to achieve the break of the score.

Refining rough cuts and sharp edges

You can make the freshly cut glass safer to handle by gently wiping the edges of the cut piece with the waste piece. This removes the sharpest edges without chipping the glass.

After the glass is scored and broken, you can remove small, unwanted chips with grozing pliers. The serrated jaws of these pliers are used to gently nibble away at the jagged edges.

Rough edges can also be smoothed with a carborundum stone. You rub the stone along each edge, upper and lower, to remove any sharp edges. You can remove more glass with the stone if you wish by a little more aggressive grinding action or just a more sustained light rubbing of the stone against the edges.

A diamond smoothing pad removes glass in much the same way as a carborundum stone, but does it more quickly with the coarser grades. You can use a number of grades to get an almost bright polish to the edges. These pads must be used with water.

A glass grinder is used by many people. Many models of grinders are available. The grinding surface of the bit is covered with fine diamonds, which grind away unwanted glass very quickly without chipping the edges. In addition, they are water-fed which keeps the glass from cracking due to heat, prolonging the life of the diamond bit, and preventing the powdery ground glass form flying around.

A glass grinder is NOT a substitute for accurate cutting.

*This section has been prepared from information provided by the Fletcher-Terry company: http://www.fletcherviscom.com/home.shtml

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