Jon Pacini on fri 3 oct 03
Greetings All--------
A subject dear to my heart ---sand vs grog-- I could go on for hours.
But I'll spare you and just give some generalities. If anyone wants to go
into details, I'll be happy to go that route too.
There are a couple of commonly used sands, silica and feldspathic, and a
number of grogs, kaolin, fireclay and a bunch of recycled crushed materials.
If you're going to be substituting Silica sand for flint fireclay grog
you stand the least chance of causing a glaze shivering or body dunting
problem. Flint fireclay is fairly high in silica as far as grogs go. First
you have to take into account the percentage of the body which is made up of
the grog to be substituted. If the body is 5% grog/sand it will have a lot
less effect on glaze fit than if the body is 20% grog/sand. An easy addition
to the body if you do end up with glaze fit problems is Feldspar. This will
fuse the free silica and will generally resolve the problem. Unless of
course you're starting with a body that is already quite vitreous, then you
should if possible reduce the silica from another source in the formula.
If you're subbing the Silica sand for Kaolin grog, then you may very
well run into glaze fit problems and body dunting. The problem isn't so much
caused by the sand granules, as it is by the fines that comes along with it.
Very few sands/grogs are strictly a specific mesh material. That is, if the
bag says 60 mesh sand, what you've got is a majority of 60 mesh sand, a very
small percentage of larger grains and varying percentages of assorted finer
grains. The amounts of the finer grains depends on the make up of the
deposit that's being mined and the way the sand is being processed. If the
the body fairly open, then feldspar will once again be an easy fix. If the
body is dense, then you must reduce the amount of silica from another
source.
If you're in an area where you have feldspathic sand avaliable and you
sub that for the grog, then you end up with a denser body. IF the body was
previously vitreous, the amount of feldspar in the formula will need to be
reduced or you may end up with warpy pots. Also the larger grain sizes of
feldspathic sand will tend to melt and come to the surface of the pot. This
usually only becomes troublesome at ^10+.
If you're subbing Silica sand for a crushed recycled material, you're on
your own----
Remember ---these are generalities and are gleaned from anecdotal
experiences----any resemblance to a specific clay body is purely
coincidental. :)
Best regards
Jon Pacini
Clay Manager
Laguna Clay Co
ivor and olive lewis on tue 22 mar 11
Dear Lee Taylor,
You could add Sillimanite to your list if your supplier has if in stock.
Be regards,
Ivor Lewis,
REDHILL,
South Australia
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