Steve Slatin on fri 24 feb 06
My most recent round of rutile tests was done as follows --
I made 4 sets of DigitalFire's floating blue glaze base,
(80% Alberta Slip, 20% frit 3134) each batch with
4 % of a different additive -- they were
1. Ceramic Rutile
2. Milled Rutile
3. Granular Rutile
4. Ilmenite
Each batch was 504 g of materials, mixed with one
measured cup of potable water, mixed with a whisk
but NOT strained. (I will do a round of tests with
strained mixes next. This allows me to test for one
more variable than if I strained right off.)
Observations -- the ceramic rutile was much finer than
milled or granular; but all three were a tan-to-brown color.
Ilmenite was not, it was black and particle size was
larger than with the other materials, even granular rutile.
All tests were fired together with a slow cool firing to
cone 6. A white stoneware (SPS's Sea Mix 5) was
used for all tests.
Visual results
1 -- an especially smooth, consistent pale blue
'float' over a tan background
2 -- almost identical background and similar
pale blue 'float' but it did not appear so consistently
on the test piece as in the case with #1. It also
appeared only where the glaze was somewhat
thicker than was the case with #1.
3 -- the base was more a clear slightly greenish
color. Instead of getting a blue float where
thick, I got black flecks. I also had some
rough areas where it appeared that the
glaze didn't completely vitrify (possibly because
of not sieving).
4 -- background almost indistinguishable from
#3, and lots of black flecks and a some gold
flecks, surface where thickest somewhat
textured but appears completely vitrified.
This glaze is almost identical in colors
and surface to the wash I was
experimenting with in August-September
with RIO and Ti mixed together in
fairly high concentration.
I was surprised, but fairly pleased. Where
once I was wondering why Ti and RIO together
didn't get me something like Rutile alone, I
now have an indication that the controlling
factor may be particle size. That is, providing
the rutile in the case of #1 and #2 is chemically
similar to that in #3, and the ilmenite is actually
different ... well, it looks different, so I'm ready
to bet it is.
Bruce G had an interesting series of tests in
response to a 'black fleck' problem with a
batch of glaze mixed with a new rutile. I can't
find this in the archives right now, but I'd now
suggest that the problem may have been that
the new batch was mixed with a granular rutile
where the previous ones were mixes with
milled or ceramic rutile.
-- Steve (still trying to figure out what to do with
5 pounds or so of milled rutile now that I want
to switch to ceramic grade, in full recognition of
the fact that Bruce is still the king of sig inserts)
Slatin
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