Wreaths

Can glass wreaths be made from bottles?

Last autumn a small group within the cooperative Jangling Space decided to see if we could make strip construction glass wreaths for Christmas.  This developed out of a collaborative project with Christopher Jeffree on whether bottle glass could be made to fit together at various sizes of frit.

Testing for compatibility of glass at frit levels

It was postulated that small sized frits did not allow stress to build to critical length beyond the frit size.  Work is still going on to discover the upper limits to the frit size for this postulation to become invalid.

We speculated that the same brand bottles from the same drinks manufacturer would be compatible.  We thought this possible, because there are few bottle manufacturers that can produce the number of bottles required and that they would have consistency.  After some experiments with same colour wine bottles we found very inconsistent compatibility.  But some volume wine producers use distinctive bottle colours, which seem to have consistency.

After some experimentation we settled on green Gordons gin bottles combined with blue bottles of a reueda wine bottled under the Four Lines brand, both of which had consistency between bottles and production runs and showed acceptable stress levels between them for these purposes. This was important to be able to distinguish by colour the stress between the frit particles. The microscopic investigation of these frit combinations did show incompatibilities, but at very short lengths.  The stress between less compatible frits was indeed interrupted by the connection of groups of wholly compatible ones.  This was successfully tested in various proportions (25%, 50%, 75%) and sizes from 75 microns to 1200 microns. Testing for larger frits remains to be conducted.

Producing the flat glass

Jangling Space had been producing sheet glass from bottles by analogy from hand blown glass — where the glass cylinder has the ends cut off, and then split — for several years.  After experimentation, it was found that cutting out a quarter of the bottle cylinder, the largest piece of flat glass could be made.  Of course, we tended toward brighter greens, yellow greens, pale ambers, and various shades of blue. This kept part of the glass pallet inexpensively supplied. 

Experimenting for the wreaths

A group of four gathered together to conduct the experimentation and preparing for a wreath making class.  Knowing that the Gordons green bottles were consistently compatible, whether as retail or bar sized bottles enabled progress toward using strips to combine into fused objects. 

 Strips were decided upon because:

• it is simple to provide parts for people with no fusing knowledge or experience to assemble,  

• there is less waste than from shards piled on top of one another,

• consistent widths of strips placed on edge would make annealing more accurate,

• It would provide a distinctive wreath pattern

We began experimenting with size, arrangement, paints, glues, Frits, glass dots, etc., to provide stability, texture, decoration.

The first element was to establish the principle, so began with small wreaths of about 15cm/6”.  These were quick to assemble on shelf paper and we tried sticking them together with CMC.  This was messy and required significant drying time before they could be moved.  The second assembly test was to use frit to stabilise the pieces.  We found we could use thin but relatively stiff plastic sheets to move the pieces on shelf paper to the kiln with little disturbance.

The pieces were fired at a 200°C/360°F rate to 720°C/1328°F for 10 minutes. This temperature was chosen as it is the softening temperature for float glass, which we believed would be enough to stick the glass together without loosing the textures of the radiating strips.  We did not use the double thickness for scheduling and annealing as is usual in unevenly thick projects.  Instead the pieces were annealed as for 12mm/0.5” although the strips averaged just less than 10mm, but of course there were gaps to be considered.

They came out looking well, and with acceptable levels of stress.  But they proved to be fragile when handled. Inspection showed that the wreaths were breaking where the attachment points were small.  This led to heaping fine and medium frit over the strips – rather than fitting fine frit between – for the next set of wreaths.  It was also felt that the wreaths were pretty dark, so we decided to add clear glass from Gordons gin bottles in a ratio of two green strips to one clear strip. At the same time some of the wreaths had some Bullseye red and white dots added to add more colour.  These were fired to 740°C/1364°F. There was little difference in texture of the strips – only a little more rounding – but the frits were more like sand than an enhancement to the wreath.  We also found that the clear bottle glass increased the amount of stress, so we went back to all green.  The dots showed very little stress, so they became part of the assembly.  

Again, although more robust in handling, they were still fragile.

Having learned

• frit can stabilise the unfired strips

• frits need to be medium to large for a good appearance

• higher temperatures are required

• only the green Gordons glass could be used

• Small Bullseye dots could be sparsely spread over wreaths

We went to a larger scale – 28cm/11”.

Stepping up in scale required a lot more glass – we found two bottles were needed to provide enough strips for a wreath.  That is a lot of 75mm/3“ strips! We produced a lot of quenched frit from the bottle necks and bottoms, which required a lot of pounding and sifting, to get rid of the fine and powdered glass.  At this scale drawing the limits for the strips became important to maintain the circular doughnut form.  Props were needed to keep the strips upright, as many of the cuts were not clean, due to the thickness variations caused by the embossing of the Gordons design on each bottle.

The essential "sprinkling" of coarse frit for a couple of centimetres (ca. 1”) out from from the centre of the strips was about two layers thick.  During the firing most of this sank into the voids between the ends of the strips, and left a "moraine" texture over the internal part of the wreath.  It gave an impression of the strips flowing out from the centre, or possibly as a retreating glacier.  It provided strength to the vulnerable/weak areas where the sides of the strips contact each other.

This increase in size needed radiating guide lines to keep the strips radiating from the centre, rather than bunching up side by side.   More short pieces were needed to fill outer gaps than expected from the smaller trials. The increased size required not only more glass, but a more robust method of transferring the unfired pieces to the kiln.  A couple of things were investigated until we discovered pizza shovels.  This was ideal to slide under the shelf paper and carefully carry to the kiln.  Also more storage space was needed, as not all the wreaths could be fitted into the kiln at once. The minor problems of scale!.

A contour fuse was used to

• maintain a lot of the undulations of the glass,

• allow some bending over to lower pieces, and

• make better contacts and incorporation of the pieces.

These fired well giving a much more robust, although heavy, wreath that was admired by the group and the members of Jangling Space. This reveal of what the group had been doing led to the suggestion of stringing LED lights and ribbons around the wreaths.

In preparation for the hands-on making of wreaths by members of Jangling Space, it was decided to make “statement” wreaths of 38cm/15” diameter.   A trial showed that three large Gordons bottles would be required to make them.  Also an additional 50% more frit required to be made.

Jangling Space members had to provide and clean sufficient bottles.  They were cut and flattened for them, and frit made from the necks and bottoms.  Each person had to cut their own strips after being shown that breaking thick glass is easier with cut running pliers without cushions.  They assembled and decorated their wreaths and the experimental group placed the frit around the inner part of the wreath.  The results were placed on a large pizza shovel and transferred to the kiln, and the waiting ones to storage shelves.

For the class that was subsequently offered, the bottles were provided by Jangling Space members who helped clean them.  Members of the experimenting group cut, flattened, cut strips, made frit and red and white balls so each class attender had a set of parts with which to assemble their wreaths. It went surprisingly well.

Thanks to Chris, Linda, Lyndsey and all the others who helped in this project.

Even Frit Distribution

A light and uneven distribution of frit that provides a pleasing image.
image credit: Donna Brown

It is often difficult to get an even distribution of frit across a background with already placed glass.

It is possible to lay down a ground of frit and build the objects (in this case bees) over the frit. It is easiest to lay down an even layer of frit with no interruptions in surface levels.

Putting the whole piece on a light sheet allows you to see the dense and light areas more easily. Use a screen mesh of similar size to the frit and sift the grit through onto the piece. The brighter light shows where the thinner application is.

Another possibility is to build the objects first, add the minimum of fusing glue to the edge and wait a while for the glue to stiffen. Then sprinkle frit evenly over everything. Sweep the frit off the objects with a soft brush into the background. View the frit distribution from a shallow angle to see the thick and thin areas, which will appear as bumps and shallows.

A possible patch to an already fired piece with an uneven spread, is to add a complimentary or contrasting colour of frit to the gappy areas and refire to exploit the uneven cover.

Playing in the Sandbox

How can sand pictures be produced in glass?

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.

What Are Alternatives to Glue?

Credit: Glass Art by Margot

Small pieces, confetti and stringers which are glued often move out of place during firings. Glue, whether dry or wet, often boils at relatively low temperatures.  This can be enough to move, or displace, and even flip light pieces.

The alternative to glue is to use a thin film of clear powder.  First arrange the pieces and then place a fine film of powder at the edges of the pieces. At tack fuse and above, the powder will incorporate with the base glass and be invisible. 

One caution is that a thick layer of powder which obscures the base glass will produce a sandpaper finish at tack temperatures, and at worst produce a multiplicity of tiny bubbles making things look grey at the finish.

In low temperature tack fuses, use a few grains of fine clear frit on either side of anything that might be subject to rolling or sliding to avoid the rough or grey appearance.

But...

If it is necessary to use glue to transport it to a remote kiln, use the minimum amount, diluted with 50% or more water, or solvent if solvent-based. Add only a small drop of the glue to the edge or end of the pieces. This avoids the glue leaving large black spots under the pieces because the burnout products cannot escape. It also prevents large amounts of glue being used.

Most of the glues have boiling points below 270°C/518°F, so a slow ramp to that temperature will create an evaporation rather than boiling and displacing the glued pieces.

A Sintering Project

Ready for firing

The project is to fire 6mm “balls” stacked 3 high onto a single sheet of clear glass without significant alteration to the base sheet or to the stacked balls. This creates a total thickness of 21mm. The proposal is to sinter the whole in one firing.

Scheduling for a sinter firing needs to be done as though 2.5 times the thickest part – in this case 52mm, or 2 inches

It is slightly more risky to do this in two firings, than one, in my opinion. A suggested schedule for sintering frit using Bullseye was:

• 100ºC /180ºF — 482ºC /900ºF, 60'  =5.8 hrs

• 40ºC /72ºF — 593ºC/1100ºF,10'      =2.8

• 20ºC /36ºF — 665ºC /1230ºF,30     =4.1

• Skip to anneal temperature, soak for 6 hours =6.5

• 6.7ºC /12ºF — 427ºC /800ºF,0'       =8.2

• 12ºC /22ºF — 371ºC /700ºF,0'        =4.7

• 40ºC /72ºF — room temperature,0’ =8.8

• Off                       =40.9 hours total or 1.7 days

This was annealing as for 38mm/1.5 inches thick. Annealing for 50mm/2” thick would need about 112 hours or 4.6 days.

However this schedule was not successful – the pieces were only lightly stuck together. Thinking about why, led to the proposal that the soak time and temperature were not long or high enough to give adhesion between the pieces.

A second attempt used a faster ramp rates to higher temperatures.

• 200°C /360°F – 540°C /1004ºF, 30’ =3.2 hrs

• 60°C /108°F -625°C /1157ºF, 30’     =1.92

• 30ºC /54ºF - 685ºC /1265ºF, 120’    =4.0

• skip to anneal temperature and soak/hold for 4 hours (as for 25mm/1”)

• 15ºC /27ºF – 427ºC /800ºF, 0’        =3.67

• 27ºC /49ºF – 370ºC /700ºF, 0’        =2.11

• 90ºC /162ºF – 50ºC /122ºF, 0’       =3.56

• Off

•  = a minimum total of 18.5 hours plus natural cooling of the kiln

This schedule used a:

• faster first ramp to a higher (540ºC /1004ºF) first soak

• a faster (60ºC /108ºF, which is 150% of the previous) rate to the lower slump temperature (625ºC /1157ºF)

• the same relative reduction (50%) in rate to a higher temperature (685ºC /1265ºF)

• a shorter (120’) anneal soak

• and consequently faster cooling rates, which showed no stress after firing

The whole structure held together and was sound. There was no apparent change in the size of the individual 6mm balls.

This difference in scheduling is an illustration of how time and temperature can be interchanged.

It also shows that size matters when sintering pieces together. Higher temperatures and more time are required for dots and balls than for frit.

More information is available in my e-book Low Temperature Kilnforming, available from Bullseye, Etsy and stephen.richard43@gmail.com

Refractory Fibre on Top of Glass

“I've made this stencil out of rigidized SilkeMat. Can I fill it with powder and/or frit and leave the stencil on the glass when I fire it to a full fuse?“

SilkeMat is thicker, with greater insulating properties than shelf paper. The base glass will be insulated in two ways. The frit in the spaces of the stencil will insulate the heat from reaching the base under it. The SilkeMat will have even greater insulating effect on the glass it covers. So, the proposed layup would create three heat areas on the base layer - the area insulated by the SilkeMat, the portion under the frit, and the uncovered areas. These three heat areas are a big problem for the glass to cope with, as they each will heat differently.

An illustration of cutting holes in SilkeMat to form a stencil with thick edges
Credit: Katie Chapman (not the origin of the question)

At full fuse the SilkeMat or any other refractory fibre blanket will mark the glass and may stick in parts.  Adding weight will only increase the marking and sticking, as well as further insulate the covered area.  The most important problem with leaving refractory papers on top of the glass during a full fuse, is the insulating property of SilkeMat or any other refractory fibre paper, creating large temperature differentials, which require extremely slow heat ups, long anneal soaks, and very slow cooling.  If it were to be fired with refractory fibre paper on top, in spite of these warnings, I would fire it as though two inches thick.

A much better approach is to make a card stencil that is stiff enough to lift easily without spilling any excess powder as it is removed.  Apply multiple thin layers of powder, firing between each application.  Careful application and firing to a low temperature tack fuse each time will give a crisp edge to the powdered image.  This can be glossed with a full fuse firing after the last application.

 

A silicone rubber colour pusher or stiff brush can move the powder, either to the powder image or away and off the base to give a crisp edge to the image.

If you have not already built the piece in the kiln, powder and frit are heavy enough that they will not be disturbed easily on the way to the kiln.  An aerosol adhesive that drifts down onto the powder will be enough to hold it in place if concerned about movement.

 

But best of all, is to create a powder wafer where the thickness and crispness of the image can be controlled, and then placing it onto the base glass.  This avoids the risks of temperature differentials being created by the refractory paper

Frit by thermal shock

Frit can be created by thermal shock.  You will still need to do some manual breaking up. The principle is that you heat the glass and then cool it rapidly, causing the glass to break into pieces from the thermal shock.

There at least two approaches depending on the type of kiln.

Clamshell and front opening kilns

Place the glass in a stainless steel bowl and heat as fast as possible to 300C – 400C. Turn the kiln off and pull out the bowl, using heat resistant gloves and dump the hot glass into a large bucket of water. 

Lidded and deep kilns

Place the glass, in a stainless steel colander, into the kiln.  Retrieve the hot glass with a hooked pole to lift the container out of the kiln and lower it into a bucket full of water.

Once the glass is cool, pour off the water and dry the glass.  When dry, you can break the crazed glass into smaller bits just as you would with other glass.  Note that pouring water over the glass has two disadvantages – one, it does not completely thermal shock the glass, and two, the large amount of steam released is very dangerous.The advantages of this quenching method of obtaining frit are that you can create frit with less effort.  You also get less fines and powder with this method. And less effort is required to smash up the glass.

Some indicate that ice cold water to quench the glass is a good idea.  This is because warm water will not provide enough of a shock to the glass to craze it throughout.  But if you have a large bucket of water, there is no necessity, as the volume of water will cool the glass quickly enough.  Of course, if you are planning another quenching, you need to renew the water, as it will not be cold enough to thoroughly craze the glass.

You can, in part, control the size of the resulting frit.  Firing at 300C/573F results in larger frit than firing at 400C/753F.  However, firing at 500C/933F does not provide even smaller frit.  The best results are between 300-400C/573-753F, although frit can be made at 200C/392F as well.  Experiment with temperatures to get the frit you want.

Once you have dried the frit, you can begin to break it up. Some can be done by hand, but the pieces are often sharp, so gloves are essential.  The other standard methods of breaking up glass to make frit are applicable. But it does not take as much effort as breaking from cullett.

First published 2018, revised 7.2.25

How Much Frit is Too Much

Scheduling for powder and frit.

 

Bullseye  pumpkin orange medium frit 00321.0002
Cedit: Bullsye Glass Company

“How much frit is too much for thickness calculation?”

There are differences between powder and frit effects on calculations for scheduling.

Powder needs to be about 2mm thick to provide strong colour, and will thin to 1mm or less during firing, so there is unlikely to be any significant effect for scheduling.

Fine frit sizes for Bullseye are between 0.2 and 1.2mm, so a single thickness layer will not affect the firing.  However, several layers thick over a portion of the area will make up to a 3mm layer and will need consideration in the scheduling.

Medium (Bullseye) frit is 1.2 to 2.7mm, So, a concentrated layer of medium and larger frits needs to be treated as an additional layer when they cover significant areas of the glass.

Scattered frits of any size with proportionate spaces between the frit will not need separate consideration in the scheduling.  Frits used to fill spaces between pieces of glass will have no effect on the scheduling either.