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.
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| 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.
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| 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.
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| 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.
 |
Moving the frit with a skewer
|
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.
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| 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.
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| 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.
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| 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 120 minutes
55°C/hr to 427C for
0 minutes
99°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 to 482 for 120
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
Both these schedules assume the final thickness of the glass will be 6mm. 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.
 |
Untreated result of pressing
|
If the surface of the glass is without sticking kiln wash or
other marks, you can use it with the matte surface without further kiln work. You can also fire polish the piece to get a glassy surface, 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 with clear. Place the spacers at the
corners of the shelf for 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.
