People seem to avoid kiln wash. Some reasons are:
- It is messy.
- It requires effort to renew.
- It needs drying between coats.
- It needs drying before firing anything on it.
- It has lots of visible brush marks.
- It must be renewed frequently.
- It is dangerous.
These notes are to clarify some misconceptions about kiln wash use. Kiln wash is an economical glass separator that requires a little effort to use, but is effective and has less health risks than other separators. Kiln wash is a separator, not a series of layers built up thickly. Some characteristics to consider in its use.
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| Thickly applied kiln wash on a mould |
You mix
the powder with water. Use a thin mix - 1:5
by volume. There are various
descriptions of the thickness of the mix.
Adhering to the 1:5 mix will ensure the right runniness of it. The mix must be frequently agitated to keep
the kiln wash in suspension while you are applying it. If you do not ensure all the kiln wash is in
suspension, you will not be applying enough separator.
Application
Use a soft bristled
brush such as a hake or broad squirrel brush to let kiln wash mix flow onto the
shelf or mould. Hold the brush almost
vertically and allow the kiln wash to flow off the brush while only lightly
touching the shelf with the bristles. Apply four thin layers in all directions – up/down,
horizontal, and the two diagonals - to ensure coverage.
 |
| Gentle application of kiln wash with a hake brush |
Drying
No drying between coats is advisable or necessary. The addition of a wet coat over the dry will wet the previous layer(s) and will lead to clumping. It is not like painting wooden table that requires drying between coats. For kiln wash all the coats should be applied without any drying between the directions of brushing. View this as applying one coat. And that is all that is needed.
Once the surface
has a dull look, it is ready to use, even though not thoroughly dry. At this stage, or later, you can remove any
brush marks. Place a sheet of paper over
the kiln wash. Smooth it by moving the
paper with the palm of your hand over the surface. Gently remove any dust.
Firing a newly kiln
washed shelf or mould with the glass on top will dry the kiln wash before glass
is soft enough to stick to it.
Removal
It is advisable to
remove the kiln wash once it has been fired to full fuse. The kaolin in the kiln wash becomes
increasingly crystalline as the temperature rises. It is fully crystalline at
about 900ºC/1650ºF. At the first full fuse it does not stick to transparent,
but often to some opalescent glass. On the second full fuse the kiln wash
sticks to all the glass. At tack fuse
temperatures, the kaolin has not fully crystallised, and several firings can be
achieved without difficulty. Experience
will show how many firings - at your tack fuse temperature – are possible.
Re-coating
Painting over used dry
kiln wash has the same difficulty of clumping as when initially applying. It is also easier to remove kiln wash that
has been fired only a few times. Kiln wash fired to full fuse several times requires
much more effort than one fired to full fuse once.
Safety
Kiln wash contains alumina hydrate and most commonly kaolin. The powdered forms of these are irritants, not health hazards. It is advisable to protect yourself and your work area. Wear a dust mask when removing the dry kiln wash. Do this is a well ventilated area or outside to reduce the dust in your studio. Dispose of the used kiln wash in sealed bags to avoid spreading the dust during refuse operations.
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