Snail Scott on thu 29 may 03
At 08:14 PM 5/28/03 -0500, you wrote:
>You have made my day about sieving. It seems to be a big part in glazing
>but with all the little particles crushed out by the roller, I figured this
>would work.
Some particles don't crush easily. But sometimes it
doesn't matter. Glazes really need a sufficiently
small particle size to melt thoroughly together, and
'chunks' don't add their substance into the chemical
mix as readily. But not all glazes contain materials
prone to outsize chunks or clumped particles. IF
your proposed glazes are of this sort, you may be able
to skip seiving. Other glazes are actually a bit more
interesting unseived, as the irregularity can yield
a more varied appearance. Some glazes really do need
it, though, and look nasty without it. They may also
be less stable chemically, since some of their
component minerals may not have evenly entered the
melt.
I use a fairly limited range of glazes, I don't
make functional ware, and I feel no need to follow
practices that don't appear to improve my work. But
I got to this point through experimentation. MY
glazes mostly do fine without seiving, as do many
others, but it's not true of all glazes. You can't
just go with statistical odds, and say, "70% of
glazes are fine without seiving, so mine probably
will be, too". (For one thing, I just made up that
number!) These are many, many glazes out there,
and I doubt that the ones I've tested are a good
statistical sample. After all, I only want certain
things from my personal glazes, and entire types of
glaze and glaze materials have never warranted my
attention. For another thing, it wouldn't matter if
99% of ALL glazes don't need seiving, if the ones
YOU want to use are in the remaining 1%.
Since you are just finding your way toward the
glazes you want to use, I would suggest seiving,
for now.
Take your 100-gram batch and dip a test tile, then
seive the remainder and dip another test. (Record
which is which.) ;) If you can't see any
difference, you can probably skip seiving that
glaze in the future. If you can see a difference,
you've just tested (essentially) two glazes at
once, so choose your favorite!
I can't tell you from here whether your rolling
method is sufficient as a substitute for seiving,
since seiving really serves two roles: breaking up
clumps and distributing the material more evenly
through the glaze, AND removing chunks that are too
large, which sometimes include foreign material.
Clumps may respond to being broken up by rolling,
but chunks may not. Try testing an unrolled glaze,
then roll the remains of the same batch and test
that. Then seive what's left and test it as well.
I know this sounds like extra work, but every
variation you make in processing your glaze is
really a new test in its own right, but without
all the extra mixing! ;) And if you do end up
with a glaze that needs seiving...honestly, it's
not that much work, especially compared with the
whole rest of the ceramic process, and it may end
up being not much more effort that your 'rolling'
method. Remember, seiving 100-gram batches is
tedious, but when you make up larger batches for
use, it's only a little more work to seive all
that extra glaze. I suspect that your rolling
method, while quick for test batches, will get
to be a pain for multi-gallon quantities, and
you definitely want your test batches to
resemble the final glaze as closely as possible.
IF your comparisons on the test tiles show
negligible variation, take your pick, but don't
test using one method then make your full-size
batch using another.
-Snail
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