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Basic Internet Glaze Course

By Lili Krakowski

 

We now have an idea of what constitutes figuring out a diet.  My friend
Debbie Dietician tells me that for some conditions a low protein diet high
in carbs and fats is desirable.  Other patients are put on diets low in
fats, or low in carbs.

In other words a diet-like a glaze-is designed around certain ingredients to
achieve a specific goal.

In glaze,  the ingredients are minerals, and the goal a particular type of
glaze-shiny, dull, opaque, translucent.  While calories are the parameter of
diet,  temperature/cone # are the parameters of glaze.

Of course, in the old days, potters threw together what was available to
them: soda, lead, ash, clay, sand.  None of this was scientific in the way
we think of science, but it was empirical and worked for them.

We live in a much more sophisticated time, getting materials from all over
the world, and can know with great accuracy what is IN the materials.  We
can, and do, get informational sheets from  our suppliers which tell us that
this batch of feldspar differs a little from the previous batch with the
same name.
 
This  is nothing to get excited about. Our materials are mined, and mine
runs vary, and then mines run out, and another mine takes over.  Some
materials are imported, and some are imported from more than one place.
 
We calculate glaze to figure out the amount of melter, the amount of
"sticker", and the amount of glass maker we want (if we want to create a new
glaze)  or to find out what is in a glaze recipe we have or get, or to find
out what might be wrong with a glaze that does not work right.
 
The formulas we calculate are called "empirical"  or "molecular".  The
adjective[s] required to tell that this is not high chemistry, but a
practical, easy way for a simple potter to get a good idea of what is going
on and what she is doing.
 
To begin:
The oxides we use are divided into three groups.  The melters or fluxes form
the RO group, the "stickers"  the  R203 group, and the glass formers: the
R20 group.  This RO business simply means one atom of the material proper
and one atom of oxygen.  There is much more to be known about these
divisions, but you can read up about them on your own.  For here and now,
the RO group is also called the Basic Oxides, the R203 group Amphoretic, and the RO2 one Acidic.
 
The RO group is the determinant of the character of a glaze.  The stickers
are Alumina (Al203) and Boron  (B2O3),  and the prime glass former  Silica
(SiO2)
 
Boron is placed with the stickers in the US and with the glass-formers in
the UK because actually it performs both functions. And, more confusing,
boron is considered a flux by some because replacing some alumina with boron lowers the glaze's melting point.
 
Alright so far.
 
Most books start their calculation section with a formula to be transformed
into a recipe.
 
I will start with an IMAGINARY recipe to be calculated into a formula, because in practice that is what we do/need most.
 
 Whiting     32
 Zinc           12
 Dolomite     15
 Clay            24
 Flint            17
 
 Ok.  How do we transform this into a formula?

 

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Originally written for Clay Art Listserv and reprinted here by kind permission of Lili Krakowski.