bill edwards on mon 20 mar 06
Think in terms of styrofoam and try to picture it on
fire and when that piece of stytrofoam has finished
burning what do you have left to weigh? Very little
would be weighed because of the composition of the
material it is made from. Clay and glaze work in a
similar nature under combustion as does any product or
material that burns. The styrofoam will lose a huge
ammount of its weight, clays and glazes sometimes lose
more weight than others where the composition is
different. This is you Loss of Ignition meaning this
much weight has went out the chimney or room or
somewhere else. That is the term for LOI. Don't
confuse it with LOL which is often used as a short-cut
in computer jargon for Laugh Out Loud.
When you see LOI at the end of a chemical analysis you
are seeing how much that material losses weight after
being fired to a prime temperature range associated
with the use of that product and potential end use.
In geology the weight is measured by using weighed and
dried for 24 hours, crucibles (product) balanced by 4
decimals. Fired to 550C dessicator for 2 hours, a hot
pull using tongs is done and then replaced back for
another 3/4 hours, I call this flashing the
dessicator. They are cooled in the dessicator and
allowed to cool and weighed again. The percentage of
dry weight is calculated and the balance of the
remaining material can be used for carbonate analysis.
However there are different ways to do this but this
is an example to kickstart your thoughts on this
wonderful thing we call chemistry. Anyone can learn it
with some effort just like calculations but you have
to start from somewhere and have good guidance and
proper information that isn't confusing. LONGER
statements often are used by me to by-pass too much
over-the-head stuff that most won't understand quick
enough to get there from here, anytime soon that is.
Ivor and Dr. Ed and a few more can talk like this
forever but they are investigative and one is a
toxicologist with a past history in testing and
understanding the mechanics. He better start answering
me before I have to go to Canada and check his pots
for LOI and extractives.
I looked at several way to check LOI and you will get
confused. Try and use the first thing that comes to
mind and that is everything will lose weight if it
will burn and therefore gives off gases under fire or
combustion. Another way to give it a look over is to
think about why you would put a piece of pottery in
water and perhaps boil it and then weighed to see if
it is pulling moisture back into the clay or glaze
body. A sponge gains weight, burn the sponge and it
loses lots of weight and cannot be put back into use
in this case as can many of the materials we use. Rice
hulls and other materials contain fine silica often
used in ash glazes as well as other minerals. I think
I read about this in here but many plants will offer
various materials to your glaze by using the left
overs from complete combustion and possible cleaning
the alkaline source by water washing several times.
This alkaline water is caustic and can be boiled and
concentrated to the point of it being very dangerous
and can cause blindness and skin burns. There's
several different answers all starting from one
question. I have used cautic sodas in some of my
testing and formulating in the past. Nasty crap!!!!
ROFLMAO - You can figure that one out but sometimes I
do this when I read clayart. If you need to know and
can't figure out ROFLMAO someone else can tell you or
write me off-list.
Bill Edwards
http://apottersmark.blogspot.com/
'Studio Pottery Set-up for Sell, offers considered!'
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