A
lot of devitrification resembles dirty smears over the glass that
will not clean away. This kind of devitrification results from
inadequate cleaning.
The
glass needs to be made “squeaky clean”. The glass needs to be
free of dust, oils and minerals before firing. An initial wash of
the glass with a minimum amount of liquid soap will dispose of the
dust and oils. However it may leave behind minerals and additives
from the soap and water, so a rinse in clean water followed by a
polishing with unprinted paper towels or lint free cloths washed
without softeners. As the glass dries you may very well hear the
squeak of glass that is well polished to dry.
If
there are still residues of labels or markers, use of a spirit may be
required to remove these marks. Then the glass will have to be
cleaned again in the normal way to remove the residues from the
spirits.
If
you are fortunate to be in an area with very few minerals in the
water, you will not have to take as many precautions as those in
areas with hard water. If you have hard water, you may need to think
about using distilled water for the final rinse if you have streaks
of devitrification after the standard cleaning process. The use of
spirits is not necessary. The glass still needs to be polished dry
with unprinted paper or dedicated towels.
An
alternative (that I use most often) is to use a window cleaner
without additives, such as supplied by glaziers. This avoids the
local water supply, and most often is sufficient to remove dust and
oils.
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