Sometimes
in a completed piece a grey line appears between pieces or at the
edge of the whole piece. Most often these are the result of grinding
the edges to fit with each other, which leads to devitrification.
In
scoring and breaking glass to fit into a fusing project, there are
often adjustments needed to the pieces for a good fit, so processes
need to be used to minimise grinding.
The
obvious preventive is accuracy in scoring and breaking to get a good
fit without adjustments. This reduces the need for changing the
shape.
Many
people use their grinders to make the adjustments required though.
Most grinders use a medium or coarse grinder bit. This leaves many
pits in the edges of the glass, requiring a significant amount of
cleaning to remove glass dust from them. The general practice is to
place any ground piece immediately into water to avoid the glass
particles drying into the pits. This is rarely sufficient to avoid devitrification, because the surface of the edges are not smooth, enabling devitrification to grow on those rough areas.
Fine
grinding heads are available and should be used when adjusting sizes
for kilnforming. These need to be cleaned just as for the coarser
grits. The results of grinding with a fine grit bit (or to 400 grit
with other tools) is usually enough when clean to avoid
devitrification.
Another
way to eliminate the appearance of grinding lines is to avoid
grinding altogether. If adjustments are necessary, groze the glass
to shape. The slight irregularities will be accommodated by the
movement of the glass during contour and full fuses. Larger spaces
between glass can be filled with powder of the same colour. If the
joint has different colours, use the powder of the darker or denser
colour as it will fill the gaps with less evidence.