Wednesday, 26 February 2020

Incompatibility or Annealing Stress?

Incompatibility or Annealing Stress?

It is sometimes difficult to determine what the cause of any cracks might be.  There are a variety of possibilities with pot melts and other high temperature processes.

Surface of slumped melt

Cracks only on the top of a piece indicate a stress problem. Yes, there may have been a shift in compatibility, due to long soaks at high temperature. It would be a small shift though, or the cracks would have progressed to be more obvious.

Possibilities of healing the cracks relate to the kind of stress. If the stress is from incompatibilities, there is no means of healing the cracks.  Further firing may worsen the problem. 

If the stress cracks are due to the annealing being inadequate, a very slow rise in temperature to about 40°C above the annealing point before going to a full fuse is required. To heal the crack, you will then need to go to full fuse temperature.  This may require dams to reduce the expansion of the piece, if that is critical. Then follow with an annealing that has a longer soak and slower anneal cool than previously used.

Slumping will not help. Yes, the compression may bring the open cracks together, but temperatures are not high enough to heal (if possible) any cracks or imperfections. 

The pattern of splits on the bottom of the slumped piece

In this case splits developed on the bottom during the slumping. The splits on the bottom - if not due to incompatibilities - are usually due to a too rapid rate of advance in temperature in the early stage of the heat up. 

If it is thought that the cracks occurred as a mistaken combination of, say Bullseye and Oceanside, the stress would have been great enough to break the piece completely.  There is too great a mismatch of these two glasses to co-exist in one piece.  Of course, if only one or a few pieces were mixed in, this kind of small crack could occur, but it will normally be around a particular colour.

It is possible that different manufacturers’ glasses were used in this piece. The differences in compatibility can produce mild stress within a piece that do not break immediately.  In high temperature process like this, the incompatibilities will be exaggerated more than in thinner pieces fired at lower temperatures.

Monday, 24 February 2020

Lead Light Cement

You can make your own lead light cement as the materials are fairly common and safe to use.  I have altered the original recipe through experience.  Too much of mineral spirits dries out the mix so quickly that the linseed oil cracks early in its life.  This results in the possibility of water leaking through the cracked cement.  One third or less of the dryer (mineral spirits) reduces the chance of too rapid drying.  I no longer use a drier at all.  This is my modified recipe.


7 parts whiting/chalk
2 parts boiled linseed oil
(measured by volume)
1-2 Tablespoons colorant
This can be lamp black (carbon), black poster paint, concrete colorant powders, or black oil paint in sufficient quantity to give a black or dark gray colour to the otherwise off-white colour of the whiting and linseed oil.  

Do not use water based colorants, such as acrylic paint.  This does not mix with the linseed oil. Instead it forms a collodial mixture that interrupts the formation of the long linseed molecular chains that make it so good as a long term sealant.

The mixed leaded light cement


Add the whiting (reserving about one quarter) to the linseed oil. Mix this well, by hand or with a domestic mixer capable of mixing bread dough. When these are mixed thoroughly, check the consistency. It should be like molasses on a cold morning - barely fluid.  At this point, add the colorant, so you will know the current colour and can adjust to make it darker.

Add more whiting as required to get the consistency you want. Experiment a little to find what suits you best. If you have to deliver the panel quickly, for example, you need to increase the proportion of whiting to make it stiffer. 


You should make only what you will be using on the current project, as the whiting separates from the linseed oil and sinks to the bottom in only a few days. The commercial cements have emulsifiers to keep the whiting from settling and so extend the life of the product. Since making your own is cheap and quick to make, there is no saving in making a lot.

Lead light cement is a simple, inexpensive sealant for leaded glass that you can make for yourself.

Wednesday, 19 February 2020

Rates of Advance for Thick Glass

Rates of Advance for Thick Glass

How fast can I heat up thick glass?

This is a frequent question.  There are general answers and some detailed work has been done – mainly Graham Stone’s Firing Schedules for Glass, the Kiln Companion and Bob Leatherbarrow’s Firing Schedules for Kilnformed Glass, JustAnother Day at the Office.

A general approach which is generally successful is to work out the annealing part of the schedule first.  I know, it seems backward.  But if you know the speed at which you will do the final cool, you can use that speed as a suitable initial rate of advance for the un-fused piece. If the glass will survive the cool down rate noted, it stands to reason that it will survive through the brittle phase of the firing too.

You do need to be a little more cautious for the 6mm and 12mm schedules as given in the Bullseye chart for annealing thick slabs.  As an example, Bullseye recommend a final cool down of 300°C for a 12mm piece.  You will find eleswhere that an initial rate of advance of 150°C for 6mm and 12mm is acceptable up to 540°C, so should be adequately safe.  Use this rate rather than the final cooling rate listed in the chart for these thicknesses.  The final rates as given in the chart for even thicker pieces are suitable initial rates of advance.

These rates are for full fused pieces that are of a single thickness all over the piece.  If your piece is tack or contour fused, you should consider using the final cool down speed for one and a half, or twice the actual thickness, as your initial rate of advance.

These rates may seem overly cautious, but you can experiment with other rates depending on the complexity of your pieces.  The experimentation can be on clear glass assembled as the final piece will be.  If you use float glass, remember that it is more acceptable of fast rates of advance when transferring the results to fusing glass.

Wednesday, 12 February 2020

Tears in Slump

An enquiry was received about a tear in the slump of an intended bowl. It was reported that it was tack fused, giving a variation in thickness between 6mm and 9mm. The blank was tack fused with the following schedule: 
139°C to 560°C  30
222°C to  621°C  30
139°C to 786°C  15
9999  to  515°C  120
60°C   to 427°C  10
115°C to  350°C  10

This is a bit odd, as it had a slow rate of advance to top temperature and no bubble squeeze. But it should not have been a problem for this piece.

It was then slumped. When the kiln was opened after the completion of the slump, this split was revealed in the centre of the bowl, rather than a complete break.

The schedule was again a bit odd and high:

83°C to  148°C  15
167°C to  590°C  10
83°C   to 720°C  10
222°C  to 410°C  120
83°C    to 427°C  10

The very slow start would protect against any heat shock, but the schedule doubled the rate of advance while the glass was still in the brittle phase.  This possibly induced some stress into the glass.  There is no reason why the rate of 167°C per hour could not have been continued to about 630°C to 640°C.  There is no need to slow the rate of advance once the glass is out of the brittle phase (ca. 540C).  With this slow rate of advance, the bowl may have been slumped into this simple ball mould at 620°C or less.  

This indicates that observation is needed when trying new layups and moulds to find the appropriate temperature.  It reveals at what stage any problem occurs.

There are several possibilities to consider in diagnosing the failure of this piece.

Rate of advance 
It might have been just too quick for the thickness of the piece. The piece is reported to have varied from 6mm to 9mm. From the picture this might have meant a single layer base, or more likely, a two-layer base and then the two-layer top pieces, making it 6mm to 12mm.  The firing schedule would need be as for an 18mm piece in the first instance, and 24mm in the second.

The initial rate of advance is more than slow enough for the calculated size of the thickest. The doubling of the rate of advance in the early stage of the brittle phase of the glass is more problematic. It may have had the effect of inducing a weakness (stress) that became apparent in the next segment with a slower rise to the top temperature. It probably heated the top much more than the bottom during this second segment, leading to the tear.

Was it adequately annealed?  
If you look at the fusing schedule, the anneal soak and anneal cools were adequate for a 12mm piece, so if compatible glass was used, there should be no annealing stress in the piece.  It is important to consider this, as a stressed piece can often break during an otherwise adequate slump schedule.

The placing of the piece may have had a significant effect on the outcome.  It is placed in the corner of the kiln.  A single element shows around the side of the kiln.  This would not be enough to heat the whole kiln, so we must assume it is mainly top fired. If the kiln has significant differences in temperature (only as much as 5°C), the location in the corner may have had enough of an effect to cause the stress.

When did the split occur
It is possible that the split occurred on the way up and then re-attached during the slow rise to the high working (lamination) temperatures.  This would give the appearance of an incomplete split, commonly called a tear.  We don’t have any information about the state of the edges. At 720°C an early split could have re-attached. The reason for considering this possibility, is the change of curve on the left end of the split. However, this does not seem likely as the split clearly shows on the edge of one of the squares, but does not go all the way across.  Lamination temperatures are not high enough to seamlessly heal a crack.

It is most likely the split occurred during the rise in temperature.  The reason for speculating this, is because of the distortions of the squares.  If the split occurred before any significant slumping the distoritions in the squares would be explained.

Range of Considerations

This discussion shows that there is much more than just the schedule to consider in diagnosing failures. 

Yes, the schedules are odd, but not impossible to get a good result with.  The fuse and slump schedules vary to a large extent which is not ideal.  

The fuse schedule to the bubble squeeze temperature is sensible, but the slow rate of advance is continued to the top temperature, which is not usual.  This means there was no consideration of a bubble squeeze soak, although this did not prove to be a problem. The annealing is suitable for up to 12mm.

The slump schedule starts very slowly and then doubles early in the schedule.  This rapid change of rate early in the brittle phase of the glass may have induced stress that could not be relieved later in the firing. A simple single rate of 167°C to the slumping temperature would have been adequate. 

The slump temperature used is in the lamination/sharp tack range, rather than the more usual 620°C to 677°C range.  This can bring several problems with excessive marking of the bottom of the piece, shrinkage, and even uprisings at the bottom of the piece.

Are any of these criticisms of the schedules adequate to point to as causes of the break? Without handling the piece, it is difficult to tell with the information available.

General Diagnosis

You need to consider the state of the break in diagnosis.  We do not know whether the edges were sharp or slightly rounded. It is clear the split piece fits the mould as it is, so the break probably occurred on the way up in temperature.

Was the high slumping temperature an element in the break? The third rate of advance was slow, so there should be no further stress introduced in the firing.  The annealing of the fused piece seems adequate, so a stress fracture does not seem likely.

The high slumping temperature may be disguising a problem, as the glass may have re-attached at the upper temperature.  But this does not seem likely as the picture seems to show the crack enters the red piece a short distance, but not all the way through.

Was the placing of the mould problematic? It is in a corner where there may be enough difference in temperature across the glass to induce this kind of tear.

These considerations show that multiple images of a problem piece need to be taken.  Various angles are required to eliminate problems with reflections.  Pictures of the whole setup in the kiln and the piece are needed.  Multiple pictures of the top and bottom are needed. And of course, close ups of the area(s) concerned.  These are all substitutes for handling the piece itself.  

If you have a community of kilnformers or a store you can take the piece to, you are likely to be able to give responses to questions and to get the information required about the possible problems and solutions.

Sunday, 9 February 2020

Pricing, 1 - Establishing the Cost

Pricing your work is necessary to get a fair return for your effort and to make an income.

Establishing the Cost

The first step is to calculate the amount it costs to run your business. Prepare a summary of annual outgoings including:

  • Studio/workspace (or as a proportion of the house that you use for a home studio)
  • Administration costs
  • Equipment & loans
  • Packaging
  • Marketing materials
  • Advertising
  • Incidental expenses
  • Income tax & social security payments
  • Insurance for public liability, materials, equipment, and employment
  • Depreciation (cost to replace things you are reliant on). The amount or proportion varies according to jurisdiction.
You will need to make some guesses about the amounts and that is OK. The value you put on some of the things above may be “zero”, but still need to be considered. All these are considered to be the overheads of your activity.

2. Step two is to calculate the time available to make your work over a year. If you are full time, start with 365 days and then subtract the weekends (104), holidays (say 10), administration time, and allow a contingency for sickness, etc.(say 10). That leaves you 241 days, less the administration time.  When you first start in business you are likely to spend 40% of your time on administration, but you should get more efficient and this time will reduce to around 30%.  So, even when fully up and running you will have about 169 days out of the 365 to spend on producing work - at best.  This means that you will have about 46% of the available time spent on production.

If you are working part time you need to do the calculations on the basis of the number of days you have available and do the subtractions and calculations as for a full time basis.  You may find your overheads are proportionally higher than fulll time, as these costs continue accrue whether you are in the studio or not.

Then do the calculation:

Overheads & personal salary (you do want to pay yourself - I insist!) divided by days available to work.

This enables you to fix a price for your time and gives you a daily rate from which you can calculate an hourly rate.

3. Step three is to estimate how long it takes you to do anything - preparation time, research, selling, marketing, packaging etc.

Add together the cost of materials and charge for the time it takes to make the item at the hourly rate you have calculated. This enables you to calculate a price for the item. Then look at how much the market will pay for your type of work.

Even if you know the market will not stand the full price, you should still do the calculations to find out the price that you should be trying to achieve.  If the price is unrealistic, you need to look at simplifying the item, or to consider different items.

All these calculations need regular reviewing.

More information is available 
Establishing the costs
Creating a pricing structure
Terms and conditions of sales
Customer relations


Pricing, 2 - Pricing Structure

Creating a Pricing Structure

After calculating what you are going to charge, use the prices to create a pricing structure:

  • Selling price to the public - recommended retail price
  • Wholesale price/trade price
  • Sale or return price
  • Selling direct to the public

The selling price for the public should be the trade/wholesale price times two, plus tax. This means that the wholesale price is your bottom/lowest price that will give you a profit.

You should set your prices to realistically cover your costs, including time spent at an event, and know what you need to charge to make a profit. You charge double your wholesale price to cover your own costs of sales, such as packaging, stand hire, etc.

Do not undercut your other outlets, otherwise they will no longer want to sell your work.

Use selling to the public as an opportunity to test the market by exploring new products and new prices.

Selling to trade

The prices you offer to trade, i.e., your wholesale prices should cover your costs and provide some profit.

Galleries and shops have enormous overheads, which is why they put so much of a mark up on pieces, but remember they will be selling your work all of the time, so you can produce the work without interruption.

Before approaching wholesale or trade outlets you need to decide on:

  • Minimum order quantities.
  • Discount prices, and quantities to qualify.
  • How much of your work they will need to make a good display (it is in both of your interests to display your work as well as possible).
  • Consider charges for carriage or if you want to offer carriage free.
  • Agree what the payment terms are – pro forma, payment on delivery or credit. If offering credit, ask for trade references.

Sale or Return

If you provide work on consignment (sale or return), make sure you know exactly what the terms are. Keep a close eye on the pieces, as there are risks that may or may not be covered by the seller

You do not want your work out for too long, so if it is not selling after 6 months it is time to move it. That means keeping records of where your work is and when it was placed.

Review your prices annually.

More information is available 
Establishing the costs
Creating a pricing structure
Terms and conditions of sales
Customer relations


Pricing, 3 - Terms and Conditions

Terms & Conditions

It is important to draw up your terms and conditions for both trade customers and for the public. They should include:

  • Details of your minimum orders
  • Carriage/delivery - is it free or charged to the customer?
  • What is the recommended retail price? It is useful to include this, as you will often be asked to provide a figure by shops.
  • Any conditions about display or point of sale material (if you provide any)
  • Credit terms
  • What deposit is necessary - when a member of the public places an order always take a deposit or ask for full payment in advance.
  • Details of any interest charges that you will charge on any outstanding debts.
  • Once an order is placed, get the customer to sign it and make sure they are aware of the relevant terms and conditions.

More information is available 

Establishing the costs
Creating a pricing structure
Terms and conditions of sales
Customer relations


Pricing, 4 - Customer Relations

Good Customer Relations

It is vitally important to keep a customer database and to develop good communication channels with your customers.  It may be that they will not be repeat customers, but they will surely tell others about your good service and excellent quality craft.  Get at least email details of every customer and potential customer wherever you go.

Always remember that trade customers need you as much as you need them, so keep them in touch with news.

It is also advisable, to make sure you allow enough time to deliver orders. It is better to say it will be two weeks and deliver early than the reverse. If you do fall behind, keep in touch with customers and let them know what is happening with their order. Also, remember it is acceptable to have a waiting list if necessary, as part of what the customer is buying is the exclusivity of your work. Always remember who or what else you may be reliant on, e.g., the weather, supply times, length of time for shipping, etc..

If you are contacting new outlets or customers do no more than 10 at a time so you can control or monitor the process. If someone says no to your work ask why, as it is important to know for your future business.

If you are supplying, or want to supply, to different outlets in the same area negotiate with them. Consider customising work for different shops or gallelries or offering them different parts of a range.

Be consistent and professional in the way you manage your relationships with customers.

Listen to customer feedback and develop ways for customers to make suggestions, such as comment cards.  
Keep in touch with people who have bought your work before.

More information is available 
Establishing the costs
Creating a pricing structure
Terms and conditions of sales
Customer relations


Pricing, 5 - Getting Paid

Avoiding Payment Problems

It is necessary to have clear terms and conditions established at the time of purchase. If you have put your terms on your invoice, you can enforce the conditions and take the customer to court.

Always invoice promptly. This is important for your cash flow and reduces the chances of payment problems.

Always keep good records of orders and invoices so you know what is overdue and when to chase for payment. A simple accounting software package will assist.

Maintain good communication and be professional. When you contact someone about an outstanding debt, be polite. However, do not allow them to walk over you. Be firm in your request for payment. Ask them to suggest a time scale for payment – normally people are committed to their own suggestions. But do not accept unreasonably long payment schedules.

More information is available 

Establishing the costs
Creating a pricing structure
Terms and conditions of sales
Customer relations

Wednesday, 5 February 2020

Leading - the First Glass Pieces

After establishing the perimeter lead cames, place the first glass piece into the corner formed by these cames. 

You only need to establish one vertical and one horizontal came to begin with. The other two will be placed at the conclusion of the leading.

Normally, you will be working from the lower left corner toward the upper right corner of the pattern if you are right-handed. The reverse is the case for left-handed people. 

Hold each piece of glass in place with some scrap lead and nail. The scrap lead will prevent the nail from chipping the glass. It's important all glass is held in place with nails so no shifting occurs while working in another area of the panel.

Fitting the rest of the glass to the cartoon is described here

Revised Feb 2020

Tucking Lead Came

It is most usual in many countries to butt lead cames against one another. In continental Europe the tucking of cames is more common. In this process, which has the advantages of speed and accuracy, the came is first fitted to the glass and then cut at the edge of the glass.

The first step is to cut the came to the appropriate angle to meet the lead to which it is to be joined. However before presenting the cut came to the joint, one end is lightly tapped with a small hammer to slightly curve the end of the came. This allows it to slip inside the leaves of the came to which it will be soldered.

The came is then shaped to the glass as normal. However, rather than removing the came for the next cut, the came is cut to the length of the glass, often using the glass as a guide. This end is then supported on the lead knife and tapped with the hammer to curve the end, ready for tucking into the next piece of came. Care is required so that you don’t crush the came and break the glass, nor miss the came and hit the glass or your fingers. With practice, there are few accidents.

Diagramatically, the tucked lead looks like this:

Tucking lead provides very accurate joints with no gaps for solder to fall through. Some argue it provides a stronger panel as the hearts of the jointed cames almost meet. The main immediate gain is quicker soldering.

Layups Promoting Bubbles

Intentional Bubbles
Sometimes you want bubbles. There are various ways to achieve bubble placement with certainty rather than at random.  You can use a variety of bubble powders.  There are a variety such as the UGC bubble powder – now supplemented with bubble enamels.  The use of copper oxide powder will give bubbles of varying sizes dependent upon the amount deposited. You can also use baking soda – calcium carbonate - in the same way for clear bubbles.

You can create a range of bubble textures by arranging textured glasses in various orientations.  Fine reeded glass at right angles will give a regular pattern of small bubbles.  Accordion glass will give a slightly different arrangement.  Using fluted glass at 60 degrees to one another will give you diamond shaped bubbles if you control the temperature and time.  The variety is limited only by the textures and the way you arrange the glass orientations.

Incidental Bubbles
Most inclusions – metal, mica, organic, etc. – result in bubbles to a greater or lesser extent around the objects included.  Extended bubble squeezes are required in conjunction with a sprinkling of powder or very fine frit between the inclusion and the edge of the piece.  Sometimes corner pieces can be included in the design to keep the edges open longer allowing more air to escape.

Unwanted Bubbles
These bubbles largely come from the way in which the glass is arranged. 

Single layers at full fuse will draw in at the edges and thin from the interior, allowing any air to push up and sometimes through the glass.  This is because the thicker and heavier edges resist the movement of the air from under the glass.  This resistance, added to the thinning of the interior leads to bubbles, unless the glass is fired at fire polish or lower temperatures.

This example from Danna Worley shows the effects of firing single layers

Single layers with borders compound the problems of single layers.  The borders ensure that the edges are heavier than the interior and seal air at an even earlier stage of the firing.  The bubbles will appear between the other tack fused pieces in the interior of the piece.  Again, with this kind of lay-up, the top temperature should be no more than a rounded tack fuse.

Heavy or thick borders on two-layer bases are also circumstances where bubbles can be produced.  The border on even two-layer pieces can trap air both under the whole piece and in between layers in the same way a border can on a single layer piece.  In a lay-up like this, it is best to fuse the two base layers together first and then add the decorative pieces and border in a second firing.

This example from Andy Bennett shows how, even when inducing bubbles, things can get out of hand. Here the bubbles between layers have even thinned out the bottom layer to holes to the shelf.

Encased glass pieces are a certain way to get bubbles.  If you place even a single layer of glass pieces in a pattern around the base and then cap it with a sheet of clear, bubbles will form.  This will happen even if there are clear path ways for the air to be released from the interior.  The capping glass will not conform completely to the encased glass pieces by the time the edge is sealed, no matter how long your bubble squeeze may be.  The way to avoid this is by putting the glass pieces on top of a two-layer base.  And it is better to fuse the base layer first before adding the surface glass pieces, so they do not press down unequally, leaving a thin film of air around the heavier pieces on top.

Avoidance of unwanted bubbles

There are a few ways to avoid bubbles that are not where you want them.

  • ·        Avoid using single layers with pieces on top.
  • ·        When using single layers fire with slow rates of advance at low as possible temperatures with a short soak at top temperature. You will need to peek at intervals to observe when the work is finished and advance to the next segment.
  • ·        Non-glass inclusions should be encased with care.  They should be as flat as possible before capped.  The bubble squeeze should be long – possibly as slow as 25°C per hour between 600°C and 677°C. This is to allow the glass at the centre to settle, pushing air from the centre out. Including a sprinkle of powder or very fine frit may help reduce bubble formation, as might chads at the corners or edge of the piece.
  • ·        Organic inclusions will produce large bubbles from the combustion gases.  Use a three to four-hour soak at about 540°C to allow the burnout of the organic material before proceeding to the bubble squeeze.
  • ·        Avoid borders on top of the glass.  The additional weight acts to seal the glass to the shelf and between layers, leaving air underneath to rise and even break through.
  • ·        Do not cap/encase glass pieces unless you have a very good reason.  The glass pieces placed on top will stick to the surface with less chance of bubble creation, and will become flat at a full fuse.
  • ·        If you must have a border or encased glass pieces, consider flip and fire – fire the piece upside down to a rounded tack fuse at least, clean thoroughly, then cap the piece and fire right side up. This can reduce the bubble formation.

Tuesday, 4 February 2020

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.

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.

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.

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.

When breaking tapering pieces of glass you should normally grasp the thin end in fingers or pliers and run the score toward the  thick end and ease the run of the score. When the score opens an initial distance, turn the glass end for end and run the score back to the opened one. 

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. This describes a straight line cut from a large sheet of glass.

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.  A note on the adjustment of cut running pliers.