Techno Tip: Passing Gas

Gassing: it’s unpleasant and you don’t want to do 1t in public. Well, we
all have it and it’s all natural! Still, not a good thing to have, especially
when it’s trapped and then released at inopportune times. It can be very
bad and even embarassing... for your pots and glazes. Gas is the cause
of those dreaded bubbles, pin holes and blisters, from tiny ones to big
craters. All glazes have bubbles but it’s the larger ones near the surface
that create all the defects.

All this gas comes from:
* Air trapped in the clay body or glaze layer
* A by-product (1.e..water vapor, carbonates) from the heating
of the clay body or glaze layer ingredients

It would not be a problem if all this gas just escaped nicely, quietly and
left a nice fresh scent. The thing that gets in the way is the melting of the
glaze. Once a glaze starts to melt, turn fluid and seal over, that’s when the
gases can no longer quietly escape. Instead, the gases are trapped and turn
into bubbles. I often watch my oatmeal bubble and that’s what I imagine
happening to the glaze on a pot. Oatmeal is pretty gooey or viscous,
but glazes are even more gooey, so the bubbles rise through a glaze very
slowly. The smaller the bubbles, the slower they rise or not at all. Then
when the bubble makes it to the surface, 1t has to burst and heal over.

So can you get a prescription that cures gas? Just as the doctor says... well...
some remedies work for some types. We can reduce the gas production, help
the gas and bubbles escape and help bubbles burst and heal over quicker . This
is much easier to do with cone 10 type glazes, but some minor changes can
affect lower temperature glazes as well. Use of a glaze calculation program
can help too. In general, these are some of the things you can look for or try
to change:

* Reducing the gas-producing ingredients in the clay body.
This is difficult unless you mix your own clay body. Select a
porcelain or smooth white clay over the darker more grogged bodies.

* Reducing the gas producing ingredients in the glaze
Replace carbonates like whiting (Calctum Carbonate) with
wollastonite.

* Replace talc with dolomite and barium/strontium carbonates
with frits
(The glaze calc programs come in handy here)

* Raising the melting, sealing temperature of the glaze
(closer to the maturity temperature.)

* Replace alkalis
(Sodium, Lithium and Potassium), nepheline syenite and boron
(gerstley borate) with other higher temperature fluxes like calctum,
magnestum and zinc.

* Reducing the surface tension and
viscosity (gooeyness) of the glaze
allows the bubbles to burst and heal

overt easier.

* Look for or make an addition of
zinc oxide and/or magnesium
oxide in the glaze.

Note, a little zinc is great, but
too much and you get different
problems.

* Making the bubbles join together
into bigger bubbles so they can
rise through the glaze faster
Look for or make an addition of zinc
oxide in the glaze. A thinner layer
of glaze will be easier to rise through,
so try not to apply too thick a glaze
layer.

¢ Allow time for the gas to escape
as well as the bubbles to rise,
burst and the glaze to heal over.
Fire slower until you reach
1000 degrees C. Then hold the
kiln temperature at a slightly
lower temperature after reaching
peak temperature.

If you wanted to be a rebel and take a
different approach, you can create a glaze
that is very viscous and gooey that will not
permit the gases to bubble up and escape
at all. The result is a lot of trapped tmy
bubbles in the glaze. If it’s a clear glaze, it
will have a cloudiness to tt and if you look
closely, it’s because there are tons of tiny
bubbles in the glaze. The surface is still
nice and smooth in most cases. Glazes
with lots of boron or gerstley borate are
like this. Itll be super stiff... never runs
off a pot but itll have lots of tiny bubbles.

I hope these tips point you in the nght
direction so you can do more research and/
or testing to help relieve your trapped gaseous
condition so you can go about without worry
of embarrassment... about your glazes. ’m

still working on mine.@ Don Jung

EEE