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

Accurate cutting

Cutting glass pieces accurately is a matter of practice whether done by hand or by person-guided machines.  Computer guided machines rely on accurate instructions being given to it. This is mainly about human-guided cutting with some information on saws.

Hand Cutting

The right approach to cutting is necessary to accuracy. 

• ·        You need clean flat surfaces with only a little flexibility, with no glass shards, bumps or warps that would make scoring the glass more difficult. 
• ·        You need to work at a comfortable height – usually about 10cm below your elbow. 
• ·        You should be moving your torso and sometimes your whole body to score, following the cutline.
• ·        Your elbow should be at your side and your wrist should be fixed. 
• ·        You need to work at a corner of the workbench to be able to move your body around as you follow a curve.
• ·        Your cutter should be at right angles to the glass (side to side)
• ·        The cutter should be angled back toward you slightly, so you can see down the barrel to the scoring wheel.  Also, so any unevenness in the glass will not cause the cutter to stall.
• ·        The pressure should consistently be about 2.5kg or 7 pounds. Do not listen for the sound, as it varies between opalescent and transparent glasses.  Heavy pressure on any glass causes unwanted break outs. Score to the pressure, not the sound.
• ·        Keep a consistent speed. Variability in speed also translates to uneven pressure. Even when you could go fast in scoring, keep to a steady pace.
• ·        Score and then break each line before going on to the next.  Do not score all around the piece in one go. It does not allow for any adjustment, if the cut is not accurate.

Oil filled cutter in classic hold

These approaches to hand scoring apply to all the ways of assisting accurate cutting.

There are at least three methods to assist accuracy in addition to the basic requirements, which apply to any method you use. 

• ·        My preference is to score the glass directly over the cartoon. This involves no extra pattern making.
• ·        Drawing the lines from the cartoon on top of the glass and then moving the glass to a separate cutting surface is the preference of many.
• ·        Making pattern pieces with the space for the foil and tolerance already cut out is a preference of many copper foilers.

Each of these assistance methods are acceptable, although the more steps involved in translating the cartoon to the glass, the more chance of introducing inaccuracies.  The accuracy of the final piece depends upon the skill with which you can manoeuvre the cutter around the glass.  This requires practice. With practice, accuracy will improve.

Machines

Glass saws of several types are available to assist in getting accurate shapes.  Mostly they are narrow thin diamond coated blades or diamond coated wire.  The wire-based saw can cut tighter and more intricate shapes than the band saw can.  But you should think about the nature of glass before you get too intricate.  The breakage rate of intricate pieces in stained glass is relatively high, even in the early life of a piece.  In fused glass it is not so difficult as they normally are supported by a base piece of glass.

Accuracy in using these saws relates to:

• ·        Manipulation of the glass to follow the line exactly.
• ·        Permanency of the guiding lines drawn onto the glass.
• ·        Accuracy of the drawn lines.
• ·        Accuracy of the pattern pieces.
• ·        Allowing the machine to cut rather than forcing the glass into the blade.
• ·        Maintenance of the machine.
• ·        Maintenance of the blade or wire.

Your accuracy will increase in the use of hand scoring or machine sawing of the glass with experience.  But, the degree of your critical appreciation of your cutting results is directly related to the accuracy of cutting.  The more you say “that is good enough” the less quickly you will improve your accuracy.

Stencils vs. Saw

Saw

Frequently when people want to make a complicated shape they resort to a saw to create the shape.  This is used in both stained glass and fused glass work.  Although it may be necessary in stained glass applications, it is not as necessary in fusing.

One of a variety of saws

Stencils

There is an alternative to an expensive saw – stencils and frits.  You can make a stencil from stiff card. Place the stencil in the appropriate place. Then sift powder or sprinkle frit over the stencil.  Lift carefully and the shape is there ready for fusing.

Example of sifting powder over a complicated stencil

To get the depth of colour obtained from sheet glass, you need to apply the powder or frit to at least 2mm or 0.079". This also means that you need to go to a contour or full fuse with the powder or frit on the top surface.  You can, of course, later cap and fire again.

Example of the cutting of a stencil

More guidance on stencils is available here.

Revised 5.1.25