“How do I remove kiln wash from a mould that I have
decided would work better with ZYP?”
Once coated with kiln wash, slumping or draping moulds do
not need to be re-coated until the surface is damaged. Then it is best to remove all the kiln wash
to prepare a new smooth surface for the kiln wash. You may, of course, as the enquirer above
states, want to use a different kind of separator. The cleaning of the kiln wash from the mould
will be the same process whatever you want to do with the mould next.
There are many ways to get the old kiln wash off. Some of them depend on the material from
which the mould is made.
Metal
If the mould is made of stainless steel or other metal, the
easiest method is to sandblast with lots of air and a minimum of grit. You can also use sandpapers or open weave
sanding screens. The methods used on ceramic moulds, as described below, can also be used on metal.
Ceramic
Sandblasting is not safe to use on ceramic moulds, as the
sandblast medium can erode the surface very quickly and often unevenly.
Preparation for manual removal of kiln wash.
It is best to wear a mask during this process to reduce the
amount of dust you inhale. Spread a cloth, newspaper or other covering to be
able to easily gather the removed kiln wash and place it in the waste. Have a vacuum sweeper at hand to remove
powder rather than blowing it around the work space. Of course, if you can do this outside, there
is much smaller risk of contamination.
Dry
I suggest that removing the kiln wash while the mould is dry
should be the first stage.
Flat surfaces can be cleaned with a straight edged wooden
stick, or wooden clay modelling tool. Firmly
push it along at a slight angle from the vertical to remove most of the kiln
wash.
On curved surfaces you will need a rounded tool such as a
plastic burnisher or all nova tool for the coarse work. This can be followed up by using a stiff
sponge to clean up any stray kiln wash still adhered. If the kiln wash is
persistently sticking to the mould, you can cut a small piece from an open
weave sanding screen and use it to gently remove the most difficult remaining
kiln wash. Do not use more than light
pressure, as with heavy pressure, the screen can begin to remove the surface of
the ceramic mould.
Wet
Some people do not like the idea of the dust created from
the removal of the kiln wash being in the air at all. And sometimes, the dry removal is not
complete.
My recommendation is to dampen the kiln wash that is on the surface
of the mould. This will cause some
difficulties in removal, because a slurry is created along with the flaking of
the baked-on kiln wash. The same tools
can be used to clean the mould as when dry.
The vacuum sweeper will not be of use though. Once the kiln wash appears to be cleaned
away, the mould needs to dry to enable removal of the remaining kiln wash. Once dry,
you can use dry sponges, or the small nylon brush to clean the remaining film
of kiln wash from the mould. This
cleaning may reveal areas where the kiln wash is still adhering. These can be
dealt with wet or dry, although I prefer dry.
If you must soak the mould, I recommend that you use a 5%
solution of citric acid because it has a chelating action on some of the
components of kiln wash.
Remember that once the mould or shelf has been coated with boron nitride, it is almost impossible to go back to kiln wash again. The boron nitride fills the porous parts of the ceramic making it difficult for the kiln wash to adhere to the mould.
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