Playing in the Sandbox

This process provides flowing, abstract images that can be used as autonomous pieces or formed into other objects, such as free drops, bowls, cut for jewellery or into pattern bars.  The appearance provided is unique to this combination of using frit and pressing.

In principle, this process is the same as creating sand pictures.  The process is in three stages: making the box, adding frit, and pressing.

The Sandbox

Determine the size of the box.  It should not be more than two-thirds the size of your kiln shelf depending on thickness.  Thicker glass pressed to 6mm will spread more than thinner.  As a guide, 12mm should have an allowance to spread to about 1.3 times the original size; 19mm should have an allowance to spread about 1.5 times the original dimensions.

Cut two sheets of the same size from clear fusing glass. One will be the front. The other will be the back.

Determine whether the image you are creating will be portrait, landscape, or square.  Orient the sheets in the appropriate way to have the top away from you.  Choose the top piece of the pair and cut two 6mm strips from the designated top.  This gives you a lip to be able to pour the frit into the box easily.

Box formed with bottom and sides glued to back and front.  The filling lip shows on the right.

From another piece of clear glass cut two 6mm strips for the sides.  If you cut them the same length as the side of the glass, they will stick above the back about 3mm. You can cut this off, but it really is not a worry for the construction of the box.  These strips form the spacers to allow the frit to be poured into the box.  Their thickness will determine the amount of frit needed to fill the box.

Get out the back sheet and clean and prepare it for attaching the strips. My preferred method is to glue the bottom 6mm strip on its edge with super glue.  It is advisable to wear plastic gloves when gluing the strips, to avoid sticking your fingers to the glass.  Super glue cures quickly and does not delay the construction of the box.  It burns out cleanly without any health and safety concerns.  Place a thin film of super glue on one edge of the strip.  Attach it to the bottom by placing it carefully at the edge of the sheet.  Do the same for the sides.

  

When the strips are stuck down to the back, place  a thin line of super glue on the top edge of the strips in preparation for attaching the top sheet.  Using a strip of wood placed at the bottom of the backing glass will help in placing the sheet accurately. Lower the sheet from contact with the bottom to the strips forming the sides of the box.

When the glue is cured, inspect the sides of the box for gaps. If there are gaps, use clear Sellotape to seal the gaps in the sides. It will burn off cleanly in the kiln.

Adding the Frit.

Place the box on an easel or other support so it is slightly tipped backwards.  This helps ensure the box does not fall toward you while working on it.  It also allows the frit to slide toward the bottom rather than bouncing off the other frit.

The early stages of filling with the box on a stand

The size of frit you choose to use will affect the final appearance.

·        Generally, powder will appear greyer and more opaque than frit. This is due to the multiplicity of tiny bubbles between the grains of powder.

·        Fine and medium frit provide more clarity than powder.

·        Coarse frit provides the most clarity, but with fizzy bubbles between pieces of frit.

When preparing to place the frit in the box, it is a good idea to take small amounts out of jars and place it into small cups to avoid contamination of the main source of the frit.

Pouring the frit into the sandbox

You can use a jeweller’s scoop or a teaspoon to move the frit from the cup to the box.  Tip the frit into the box above where you want the colour to be placed.  

Using a wire to poke frit through to lower layers.  This also shows  a difference between front and back.

If the frit does not land just where you want it, you can move it with stiff wire that is long enough to reach the bottom of the box.  Gently sweep the frit with the end of the wire toward the place you want the coloured frit to be.

Using a jewellers scoop to add the frit.

Continue adding colours to create the profile and shapes you wish.

You can make additional alterations to the way the frit is placed.  You can poke the frit from one layer into lower layers with a stiff wire by pushing the wire directly downward.  You cannot do this more than 2 or 3 centimetres deep, as the frits and powders become compacted.

A thick copper wire being used to poke down from an upper layer to the lower ones.

When filled to the top or to your desired level, use the fourth strip to close the box.  If full, glue the strip to the top.  If not full, cut strip to the length needed to drop into the opening of the box.  Place a couple of drops of super glue on the top of the already placed strip to keep it in place while moving to the kiln.

The Pressing

Prepare the shelves

You will need two shelves for each pressing. One is the base to hold the glass and the spacers.  The other is to provide the weight to press the glass thinner.

Clean off old kiln wash from the shelves. Experience shows that adding new kiln wash over old for this process promotes the sticking of the kiln wash to the glass.  Add new kiln wash that performs well at extended times at upper temperatures.  I find Bullseye shelf primer works very well.

Once partially dried, with the pink beginning to pale, you can smooth the surface brush marks.  Some use balled up material such as tights to rub over the surface.  I find very good results from rubbing lightly over the kiln washed surface with a sheet of paper between the palm of my hand and the shelf.  The advantage of doing this smoothing while slightly damp is that no dust is created that needs to be cleaned away.  The disadvantage is that too much pressure will pull bits of kiln wash from the shelf.

Do not use fibre papers as the separator.  The glass will be moving within the space between the shelves.  It will pick up and incorporate parts of the fibre paper, if used.

If you have shelves of different thicknesses, reserve the thickest shelf for the upper, pressing one.  If all your shelves are the same size, put a second on top for adequate weight, or add heavy bricks or a steel weight to the top shelf.  (Note: if you use bricks for weights, they need to be dried first.  A two-hour to three-hour soak at 95C should be sufficient.)

Placing

Place the sandbox centrally on the shelf.  If you are doing more than one, ensure there is plenty of space between the pieces and from the edge, so they don’t contact each other, or drip over the edge of the shelf.  The allowances given for the size of the sandbox are a guide.

Two sandboxes placed on separate shelves

Place spacers of the desired thickness around the four corners of the shelf to restrict the extent of thinning.  This also regulates the evenness of the glass across the whole surface.  Usually, 6mm is a desirable height for the pressing.  Other thicknesses can be chosen for different purposes.  The spacers can be steel washers, although they will spall in the cooling stages of the firing.  If you have pieces of ceramic of the desired height, they can be used.  Fibre paper stacked up to the appropriate height are surprisingly robust spacers.  They also provide a cleaner set of spacers than steel.

A corner of the shelf with the 6mm fibre spacer

Place the upper shelf gently down onto the glass piece. The glass at this stage is taking the whole of the weight of the pressing shelf.  The shelf must be placed both gently and evenly down onto the glass to avoid breakage.

Check that everything is in place. This may require additional, directional light such as from your mobile phone or a torch.  It is now ready to fire.

The Firing

This assembly of materials has a lot of mass.  It is 2 to 3 times the normal mass for a standard firing.  

Pressing shelf placed on top of the glass sandbox

This promotes variations in practice:

·        Even with this additional mass, you can fire quickly.  This is because the glass is in small pieces and that the mass of the shelves gains heat slowly. 

·        The greater mass does require longer soaks than a normal fuse firing. 

·        The upper temperature for a full fuse is required to get the glass to a sufficiently low viscosity to allow the glass to move.

·        The long soak at the top temperature does not promote devitrification as in normal fusing.  My speculation is that the glass is not exposed to the air, so the devitrification cannot form. 

·        A further difference in a pressing firing is that the annealing can be at the rate for the final thickness of the glass.  The mass of the shelf and weights above the glass means the glass is cooling evenly from both sides, unlike normal fusing.  The glass may be cooling more slowly than programmed, but the programmed rates limit any possibility of too rapid a cooling.

A schedule for a 12mm thick Bullseye piece with a 19mm upper shelf might look like this:

300°C/hr to    670C       for   180 minutes

300°C/hr to    816C       for   180 minutes

AFAP       to    482C       for   180 minutes

55°C/hr   to    427C       for   0 minutes

110°C/hr to    370C       for   0 minutes

200°C/hr to    50c         for   0 minutes

Off

A piece of 19mm should be slower:

150°C/hr to    670  for   240 minutes

150°C/hr to    816  for   240 minutes

AFAP       482  for   240 minutes

45°C/hr   to    427  for   0 minutes

90°C/hr   to    370 for   0 minutes

180°C/hr to    50    for   0 minutes

Off  

The schedule for glasses other than Bullseye only needs to have the top and annealing temperatures altered to the ones appropriate to the glass.

Results

The pressed glass will have the texture of the shelves on both sides.  Normally, no kiln wash will be stuck to the glass.  If there is kiln wash to be removed, you can do this by abrasive means – sandblasting, diamond pads, wet and dry sandpapers or Dremel style tools.  It is important to keep the glass damp during this process.

If the surface of the glass is without sticking kiln wash or other marks, you can use it with the matte surface.  You can also fire polish the piece, once you have thoroughly cleaned it.

Alternatives

Tape box together

After super gluing the bottom and side strips, you can bind the box together with clear Sellotape.  Pull off at least three strips of tape and set them where you can reach them easily.  Place the upper sheet on the prepared base. Move the box to the edge of the work surface so a little of the box hangs over.  The first stage is to place a strip of tape at right angles to the side to bind the top to the bottom.  Do this for each of the three sides.  When the top is securely attached to the base and sides tape along the length of each of the three sides. 

This shows on the lower left a loosened piece of sellotape on the edge of the sandbox.

This process avoids any difficulty in attaching the top.   Attempting to use only Sellotape to bind the box together is very difficult and requires at least three hands.

Spacers for the frit

Spacers do not always need to be strips on edge.  The spacers can be one or two wider strips placed on their sides to provide the needed height.  They can be coloured, forming a border; but remember the border will become curved. The strips will need to be glued to the back.  The top can be attached with super glue, or taped to the sides and back.

Pressing without a box

It is possible to use the pressing technique without a box or frit.  You can arrange clear and coloured cullet on the shelf.  The arrangement needs to be such that there are no gaps between the pieces.  This means that the glass will probably be 3 to 4 layers thick.  Be careful to avoid creating thick layers of dark colour by interfiling clear. Place the spacers at the corners of the shelf in the thickness desired and fire.  The slower rate of firing (as for 19mm) should be used.

This sandbox process is a combination of arranging frits and pressing.

Glass Grinder Maintenance

Glass grinders are often the main machine used in stained glass.  They are important machines to many of us and so need proper maintenance and use to give us long service.  This note is about the things you need to keep in mind about maintaining the grinder.

Glass grinders are very handy tools. They mainly consists of a spinning diamond coated cylinder (the bit) extending above a grid surface that can rapidly and accurately grind glass to the desired shape.

Don't purposely cut glass large with the intention of grinding. Ideally no grinding would have to be done. It should be used only for minor adjustments or for grinding tough-to-cut inside curves.

Cleaning

The water reservoir should be emptied each day after use.  It is not advisable to have standing water in your grinder for some health reasons, avoiding unpleasant smells, and as moving a grinder with water risks damaging the grinder’s motor and other equipment and materials in the studio.  Even if you do not move your grinder about, the water needs changing just as frequently as the glass grit needs removing.  Some people line their reservoir with aluminium foil to catch the grinding residue.  This may not be possible on all grinders, but does reduce the effort of cleaning the grit from the bottom of the reservoir.

Ensure you clean your sponge (if the grinder uses one) when cleaning out the reservoir.  If you do not clean it regularly, it will become hard and stop bringing water to your grinding head.

The accumulated glass grit should be cleaned out with scraper or paper towel and disposed of in the waste, not down a sink.  The glass grit is relatively heavy and will become solid and block your drains.  If you have a garden, the glass grit is a good soil modifier, by helping the drainage.  The glass grit will accumulate and restrict the flow of water to your grinding head.

Clean any plastic eye shield with running water, as rubbing it will scratch the surface.

Ensure there is water in the reservoir before starting any grinding, but do not over fill as the excess water could get into the motor. Empty the reservoir daily. This keeps the water from producing a smell, and allows you to clear the glass residue from around the grinding bit.

Grinder Head Maintenance

Wear - There seem to be two main indications of wear – chipping of the glass, and slow grinding.  There are a number of reasons that may cause the grinder to chip the glass surface and not all are indications of wear. Some of the things to check are:

Too much pressure will cause the glass to chip.

It may be that you are pressing the glass into the grinder head too hard. The grinder head should do the work. Firm rather than hard pressure should be applied. If the grinder motor slows, it is an indication that far too much pressure is being applied. It will also lead to cuts on your fingers. Run the glass lightly against the grinder all the way around to remove any overlooked sharp shells on the glass.  Then light pressure will not cut your fingers while grinding.

This shows some finger protection being used, possibly to protect fingers from too much pressure

Grit size has an influence on the way the edge appears.

It is possible that you may be using too coarse a grit on the grinder bit/head. The coarser the grit is, the larger the chips will be taken off the edge surfaces. Smaller grits take smaller chips off the edges, and so are less obvious.

New bits can be a source of chipping.

Oddly, new bits can cause chipping. If it is a new bit that is causing the chipping, consider dressing it. New bits often need to be dressed – removing protruding diamonds, or cleaning and exposing new ones on a worn bit. To dress the bit you can grind some scrap glass, brick, or use a dressing stone to lightly grind some of the abrasive material away. This most often settles the bit and avoids chipping.

A worn or damaged grinder bit/head can cause chipping.

Inspect your bit carefully for smooth areas showing that the diamonds have been worn away. Also look for dents, and other irregularities on the surface, indicating that the bit is damaged. Any dents or smooth places on the bit cause a vibration that is similar to a tiny hammer tapping the edge of the glass.

This shows that chipping of the glass is most often comes from the way the machine is used rather than the grinder head needing replacement.

Lubrication

Water for the grinding head

Insufficient water supply can reduce the life of the grinder head.

If there is too little water reaching the head to lubricate the diamonds and keep the glass cool it can reduce the life of the grinder head, by overheating it too. If you are getting a white paste or a powder on or near the glass, you need to increase the water supply. This may indicate a low water level, too much grit in the reservoir or sponge clogged preventing sufficient water reaching the grinding head.

The white reside on the grinding head shows there is insufficient water reaching the grinding surface

Vaseline for the shaft and grub screw.  Smooth any corrosion from the shaft with fine wet and dry sandpaper and lubricate the shaft. Periodic removal of the bit and lubrication of the shaft should be part of the regular maintenance of the grinder.  Also ensure the grub screw is kept clear of glass grit by putting some Vaseline in the recess.  This keeps the threads and the slot for the alan key from clogging up with glass grit.

Removing the Head

The first step in removing the grinding head is to loosen the grub screw that fixes the head to the shaft. This is often full of glass grit, so clean the recess for the alan key first. I do this by using a needle or other thin sharp object to clear out all the glass powder from the recess in the screw and the threads. I am sure there are other things that can be used to clean out the hole too. When clean, insert the alan key as far as possible and while holding it in turn the key in an anticlockwise direction.  If it will not move, you need more leverage.  If the alan key simply spins in the recess, you need a stud bolt remover tool. 

This is a tool that many mechanics and tool shops have. It is normally square or triangular. It is used by drilling into the broken off bolt. The tool is tapped into the hole and then with a wrench/spanner the grub screw is loosened. In the case of the grub screw the recess is already there so you only need to hammer the removal tool into the alan key recess and proceed as normal.

The more modern and safer method is to use a tool with a reverse thread on it. This means that as you turn anti-clockwise, the tool thread bites into the recess and brings the grub screw out.

If the grinding bit is already seized, the method of removal is based on how fast it is stuck. If there is a bit of movement around the shaft when the grub screw is removed, you can probably remove it with simple tools. First use very fine wet and dry sandpaper to remove all corrosion and roughness from the upper, exposed part of the shaft. Put a thin film of lubrication or penetrating oil on the shaft and then you can hold the top of the shaft tight with smooth-jawed pliers while you twist the bit. Be careful not to mark the shaft or you will create another obstacle to removal of the bit. Alternatively, while pulling up on the bit, you can tap the top end of the shaft gently with a plastic hammer to shake the bit loose.

If this does not work, remove the grid and turn the dried grinder upside down and spray WD-40 or other penetrating oil to the bottom of the grinder bit.  This should be left for a few days with renewal of the penetrating oil every half day. Then try the methods above to free the bit from the shaft.

If the bit is still firmly stuck, you will need a small wheel puller to get the bit off the shaft.  Small wheel pullers are available from most DIY or mechanics suppliers.

Once you have the bit off, smooth any corrosion from the shaft with fine wet and dry sandpaper and lubricate the shaft. Periodic removal of the bit and lubrication of the shaft should be part of the regular maintenance of the grinder.

Adjusting height

If your grinder bit is too low or too high the diamond surface will not grind the whole of the glass edge. This can lead to chipping of the surface of the glass at the edges.

A good practice is to start with the bit as high as possible to allow for differing thicknesses of glass. As high as possible is with the bottom of the diamonds just below the platform of the grinder. This will ensure that you can deal with varying thicknesses of glass without immediate adjustment. You can then lower the bit as it wears.

This bit is only just high enough for this style of grinding

An example of  the right height, but you can see that too much pressure is being applied

Here the head is only just low enough to catch all the glass. It should be a little lower.

Be certain that you secure the grinding head with the grub screw facing the flat part of the shaft.  Failure to do that will both mark the shaft, making removal difficult, and potentially allow the shaft to spin while the head remains stationary.

This shows the minimum level for 3mm glass

Of course, you need to ensure there is adequate water reaching the grinding bit to avoid overheating the glass, and to keep the dust from grinding from getting into the air.

Care in Use

Lubrication

Water is the primary lubricant.  It washes the grit from between the diamonds and keeps the head cool.  It also cools the glass, of course.

You can buy an additive for the water – often called a diamond coolant – which is intended to provide a kind of lubrication for the diamonds. This may also extend the life of the bit.

Grinding head/Bits

The diamond bit must be kept wet in order to reduce wear on the diamond and prevent glass dust from developing and being inhaled. There are several grits available. "Fine" grinds slower but leaves fewer chips out of the glass. "Coarse" grinds very fast but leaves larger chips. "Standard" is a central compromise.

Shaft

Smooth any corrosion from the shaft with fine wet and dry sandpaper and lubricate the shaft. Periodic removal of the bit and lubrication of the shaft should be part of the regular maintenance of the grinder.

The maintenance is not only on the shaft but also on the fixings. Putting a dab of Vaseline or thick grease into the grub screw socket will help keep it clear of the glass residue. 

Pressure

It may be that you are pressing the glass into the grinder head too hard. The grinder head should do the work. Firm rather than hard pressure should be applied. If the grinder slows, it is an indication that too much pressure is being applied.

Extending the life of your grinder bits is a matter of recognising that you should not force the glass into the grinding head. Excessive pressure against the head heats the bit and allows the diamonds to become free of the binding material, so reducing its life. If the motor slows as you press the glass to the bit, you are applying too much pressure. That kind of pressure also puts a lot of wear on the bearings of the motor.

If the grinder is not taking glass off fast enough for your purposes, you should put a coarser bit on the grinder, rather than press harder. The bits do come in a variety of grits. Try out some different grits to find the one that works best for the speed at which you want to remove the glass.

Maintenance routine

A maintenance routine for your grinder is a practice that will reward you with longer lives for your grinder heads and the machine itself.  A sample routine might be like the following:

Daily

·         Empty water reservoir

·         Clean out glass grit

·         Clean eye shield

        Weekly

• Inspect bit for wear. Adjust up or down or replace
• Inspect grub screw is free of glass grit. Clean and re-fill with Vaseline
• Check head moves freely up and down on shaft

Stepping Stones

Making stepping stones is a relatively simple process if a few processes are followed. 

A range of examples

Work Area

Pick a work area where the mold can be left undisturbed for 48 hrs.
Prepare the area by putting a protective layer of newspaper or plastic around the work area. Place several pairs of gloves, bags of concrete, chicken wire, mould, stick back plastic, cut glass and water ready to hand. A mixing container is essential, and you should have the reinforcing chicken wire ready cut to size for the mould. A nearby dust bin is a good idea to be able to put waste into without moving wet materials far. Make sure the work area is level and the mould sitting on it is also level.

Design and positioning of glass

Opalescent glass is the best to use for stepping stones, as it reflects the light. Transparent ones appear dark or black.

The cut line cartoon should have lines at least 3mm wide – up to 6mm is also suitable. The cement needs to get between the glass pieces. Cut the glass to the edge of the cartoon lines.

Ensure the glass pieces do not come closer than 12mm to the edge of the mould to allow the concrete to form an edge that will protect the glass pieces.

Cartoon, cut glass, and examples of the process

Placing and adhering glass
Use clear sticky backed plastic and fix it – sticky face up – over your cartoon. Place the glass pieces firmly onto the sticky plastic. Cut the plastic to the size and shape of the mould to ensure no concrete gets under the glass.

Glass placed and ready for pouring

Preparing the mould

Put a separator on the mould – spray on oils can work, but Vaseline is a more certain separator. All of the mould surface must be thoroughly coated. Disposable plastic or latex gloves will help with greasing the mould.

Carefully lift the sticky back plastic with the glass on it and place it in mold making sure placed in center.

Examples of ready made moulds

Concrete mix

If you are making small quantities of cement, ready mixed concrete for general purposes will be suitable. 

If you are making a number of stepping stones ,mix the concrete yourself as it will be cheaper.

A ready mixed quick setting concrete

The ratios for general purpose concrete are 1: 2: 4 concrete: sand: stones. The water needed will be about 1.7 times the volume of the dry mix.

Calculating the amounts: Square and rectangular moulds are easiest – multiply the length by the width to give the area and multiply that by the depth in centimeters. This will give you the volume in cubic centimeters. Divide the result by 1000 and you have the total number of litres required.

For circular or hexagonal moulds multiply one half of the diameter (the radius) times itself and then times 3.14 to give the area. Finally multiply by the depth of the mould to get the volume. All of this is measured in centimeters.

You have seven parts of dry material, so divide by seven and the one seventh will be the concrete needed, two sevenths the sand and four sevenths the volume of stones needed. The stones should not be larger than drive-way type gravel.

You can of course, just fill the moulds with water and measure the water required to give you the volumes you need.

Mix up the dry materials, whether ready mixed or measured by yourself, to ensure everything is coated with the concrete.

Dry mixing and then progressively adding water

To get a fine, smooth surface to the top of the stepping stone, sieve out the stones from some of the mix to give you about 1 cm depth to pour between the glass pieces without any stones sitting there. (Multiply area by 1 cm to give you the volume of dry material you need to put down the top layer.) When you have sieved that amount of material out, put the coarser material back into the dry materials and mix again. The stones are important to the strength of the whole stepping stone.

Pouring the concrete

Mix the cement, sand and small stones with about 1.5 times water until a thick pancake batter. Pour it slowly over the glass to ensure you do not disturb the placement of the glass pieces. When poured, tap the sides of the mould with a piece of timber to encourage air bubbles to rise.

Mix the remaining dry materials with water and gently pour half of it into the mould. Then add the chicken wire for re-enforcement and fill with the remainder of the cement. The metal is better than the plastic version. 

Tap the sides of the mould again to drive air bubbles out of the mixture. There should be no pools of water on top of the cement, as too much water will weaken the concrete, as will too little. If there is excess it should be absorbed with some paper towels.

This is the time to sign the stepping stone. There is a relatively short time after about an hour to do this while the concrete is stiff enough to hold the marks and not too stiff to resist any marks.

Removing
Let the stone cure at least 48 hours before removing from mold. Do not move mold once the concrete is in it – you will get concrete between the contact paper and glass which causes the top to be uneven and more importantly can cause cracks in the concrete.

When you are ready to de-mould, turn the mould face down onto a board. Ease the sides away from the concrete gently. It may drop out with just that encouragement. If not, press gently at the centre of the mould until it beings to release. Finally, if necessary tap the sides of the mould with a rubber mallet. Difficulty in removing the stepping stone usually relates to too little separator.

Pealing off the plastic

Turn the stepping stone over with the assistance of the a board on the back. Look at the top of the stone and decide whether it is fully cured. If not, leave the sticky plastic on for a few more days before gently pealing it off. If you can see that there are gaps or depressions in the surface, you will need to take the plastic off immediately and make a small mix of concrete and sand (1:2) with water to fill those blemishes.

Clean the concrete from the glass before fully cured as it is more difficult to get the dry concrete from the glass without scratching it.

Curing
Let the stepping stone sit for 30 days before sealing. You can leave them flat or stand against a wall. In either case you should put some paper between so they don't get scratched. Clear concrete sealer, with two to four coats brushed on, will be sufficient for protection from moisture. Weather, temperature and time of year play a big part in the curing and de-molding. Do not put your mold in the sun to cure, as that dries out the water before the chemical reactions can occur. Concrete needs to cure slowly to achieve its maximum strength. For the same reason, you do not want to leave the curing concrete in freezing conditions as that will also stop the chemical reactions. If it is wet, you need to protect the curing cement from the rain as too much water can weaken the concrete too.