Needle points or spikes can give the glass edges the appearance of a porcupine.
They are cause by the glass contracting during heating to achieve a quarter inch thickness.
As the glass heats it pulls in to achieve the quarter inch thickness and this pulling in causes the glass to grasp and hold whatever it is sitting on.
These rough edges can be found on pieces that are fired on a kiln washed shelf or fusing too little frit inside a mold.
They can also be found on pieces that have been over-fired, or glass that has been heated to high a temperature and held at this temperature for a period of time.
To avoid these spiky points from appearing on your finished piece, use kiln paper, fire pieces that are composed of more than one layer and watch your temperature.
Kiln paper or thin shelf paper will act as a barrier between the glass and the shelf, thus allowing the glass to move smoothly without grabbing.
Single pieces of glass that are brought up to a full fuse will also pull to achieve that quarter inch thickness and as they pull, tiny spots can get caught and cause spikes.
When found on pieces that have been fused in a mold, it is generally found on pieces that have been constructed with frit.
If there is not enough frit for the depth and volume of that particular mold it will pull in and the tiny particles will form points as they grab the sides of the mold.
To avoid this from happening, fill the mold with frit and then fill them higher than the actual mold, forming a mound or cone look on top of the mold.
A grinder or polishing pads can be used to remove the spikes.
Be sure to clean the glass to remove any residue left from this procedure.
Fire the piece to a fire polish temperature to achieve a smooth, shiny appearance.
Determine by your particular kiln at what temperature it will achieve a polished appearance.
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Glass Fusing Problems
Problems and Solutions
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