Chris Schafale on wed 10 feb 99
I don't know if this qualifies as a "boneheaded mistake", but I sure
didn't see this coming, and hope my experience might stop someone
else from having the same problem.
Here's the scenario: A friend asks me to make a communion set for
her husband for Christmas. She wants an inscription on the bottom of
the plate. I make 4 plates, so I'll have some to choose from, but I
don't want to put the inscription on all of them because I might want
to sell the others to someone else. So, I think, I'll just glaze
all four, pick the one I like best, and then write the inscription
in underglaze and refire. Christmas is fast approaching, however,
and I don't have time to do the refire before she needs the plate. I
give it to her without the inscription, promise to do it later. She
gives it to her husband, who loves it.
A couple of weeks later, I get the plate back, write the inscription
in underglaze, and get ready to refire. I've refired Floating Blue
before to cone 5, and had some problems with the glaze getting
greenish, so I think, hmm, maybe if I fire it just to
bisque temp (04), I won't have that problem. Well, imagine my horror
when I open the bisque kiln and find that the plate, previously a
lovely, variegated dark blue with lighter blue areas, is now
uniformly a kind of yellow-green-tan color. All traces of blue have
completely vanished.
Fortunately, I still have the extra plates I made, and this time I do
the inscription with an engraving tool, the customer is happy, and
all's well that ends well.
But, for all you Floating Blue lovers out there -- don't refire to
bisque temperature! And more generally, as I have learned to my
sorrow, if you are going to refire a glaze, it's best to try it first
on an expendable piece.
Hope this saves someone else a costly mistake. And if anyone out
there knows why this glaze should behave this way when refired to
bisque, but not when refired to maturity, I'd love to know the
answer. I suspect titanium crystallization, but don't really
understand why this would happen only at the lower temp.
Chris
Light One Candle Pottery
Fuquay-Varina, NC
candle@nuteknet.com
Joshua Lynch on thu 11 feb 99
Is this glaze food safe? Most of the floating blue ^6 recipes are similiar
(RISD, Cooper, Clayart).
Don Goodrich on fri 12 feb 99
Hi Chris,
Been there, done that. The FB looked really pale and washed out when
refired to cone 04 when I tried to combine it with a low-temp glaze in a 2nd
firing. Having learned the error of my ways and with nothing to lose, I dipped
the pot in the Floating Blue bucket again (probably didn't need to) and
refired to cone 6. Voila! Better than the first time: the FB came out a rich
blue, its character restored.
So, there may be hope for that plate yet. If you haven't refired it yet,
maybe it's worth a try.
Don Goodrich in soggy, but soon to be snowy Zion, Illinois
goodrichdn@aol.com
http://members.aol.com/goodrichdn
Chris Schafale on mon 15 feb 99
An update on the Floating-Blue-turned-brown plate. Several people
wrote to suggest that I refire it all the way to cone 5 and predicted
it would turn blue again. I scoffed. Then I dipped half the plate
in Floating Blue and left the other half brown, and stuck it in my
cone 6 firing. Well, folks, it's blue again. All over. The part
that didn't get more glaze is very slightly browner in places where
the glaze is thin, and the whole thing has that greenish, "you fired
me too high" look that Floating Blue can get, but by golly it's blue.
Coulda knocked me over with a feather.
Sure would like to know just what's going on here. My best guess is,
the rutile in the glaze formed crystals in the first re-firing,
creating the tan color which covered up the blue. In the second
re-firing, the crystals melted back into the mix at the higher
temperature, and the cooling was rapid enough to keep them from
reforming. Any other theories out there?
Chris
Light One Candle Pottery
Fuquay-Varina, NC
candle@nuteknet.com
Tom Buck on tue 16 feb 99
Chris:
I rather think the explanation lies in crystal particle size
rather than some crystalline glaze now (at C06) and no crystalline forms
at C6.
My favourite author, Michael Cardew, "Pioneer Pottery" gives some
indication of this effect on Page 140 during his discussion of Iron
stoneware glazes, and opaque white glazes (non tin oxide). He has a
footnote that relates suspended in-glaze particle size and light colour
transmission. Worth checking on.
BFN.
Tom Buck ) tel: 905-389-2339
& snailmail: 373 East 43rd St. Hamilton ON L8T 3E1 Canada
(westend Lake Ontario, province of Ontario, Canada).
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