Dannon Rhudy on tue 8 aug 06
Janine said:
.......need specific gravities of UNT glazes........have to
fill a gallery by the 15th........
Hate to tell you this, but UNT glazes are hit-or-miss,
and most of them are in fact collections of glazes from
a lot of other places/persons. Neither of the professors
at UNT taught any glaze classes in the three years I was
there. But they did have huge collections of handouts
of glazes.
No way could they supply you with the specific gravity
or indeed any technical information.
"Filling a gallery" with work with unknown glazes is
risky business. A more thoughtful approach might serve
you better.
regards
Dannon Rhudy
----- Original Message -----
From: "Janine Roubik"
John Britt on tue 8 aug 06
Janine,
The first glaze is Leach 4/3/2/1 (if you retotal to 100%) and the sp. gr.
could be about 155.
(page 61 of my book)
>UNT celadon c/9-10
>Ball clay 200
>whiting 400
>silica 600
>soda feldspar 800
>
>add 2% RIO
I am going to guess that this glaze (as it has 10% gerstley borate) should
be mixed thinner. Try sp. gr. 150. Just a guess.
>
>Celadon II
>Feldspar 1400
>gerstley borate 200
>whiting 200
>kaolin 200
>silica 200
>
>add 3% RIO
>
>
This one is similar to Sam Satin Celadon which we mix at sp.gr. 158.
>Blue celadon c/9-10
>feldspar 800
>silica 600
>barium carb. 160
>dolomite 140
>kaolin 200
>whiuting 100
>
>add 2% RIO
>
This Rutile Blue is called Ray's Rutile Blue in my book, page 109. Ray
was from Dallas, TX. sp.gr. 146.
>Rutile blue
>talc 11.2
>whiting 20.5
>potash feld. 32.2
>kaolin 16.6
>flint 19.5
>
>add rutile 8.3
P.S. If you like that Rutile Blue try this one(Page 109):
RUTILE BLUE 11 cone 10
Custer Feldspar 30.00
Whiting 11.10
EPK Kaolin 16.80
Silica 26.30
Dolomite 15.80
Rutile 8.00
Hope it helps!
John Britt
www.johnbrittpottery.com
Bruce Girrell on tue 8 aug 06
Janine,
I hate to tell you this, but the specific gravity is determined by how much
water you add to the dry materials. You can mix up just about any specific
gravity that you choose. What S.G. would he like?
Bruce Girrell
Janine Roubik on tue 8 aug 06
Hello,
This is my first time posting to this.
I've recently gotten access to a gas kiln (YAAA!) And have been trying to
find some nice glazes to use. I've got a listing of some UNiversity of
North Texas glazes from the kiln owner. This guy wants to know the
specific gravities of these glazes. I also am in a time constraint and
need to fill a gallery by the 15th. The glazes this guy had listed
he "garanteed" are good but again, I need the Specific gravities for them.
Does anyone know these off hand? Is there a way to aprroximate based on
the type of glaze?
UNT celadon c/9-10
Ball clay 200
whiting 400
silica 600
soda feldspar 800
add 2% RIO
Celadon II
Feldspar 1400
gerstley borate 200
whiting 200
kaolin 200
silica 200
add 3% RIO
Blue celadon c/9-10
feldspar 800
silica 600
barium carb. 160
dolomite 140
kaolin 200
whiuting 100
add 2% RIO
Rutile blue
talc 11.2
whiting 20.5
potash feld. 32.2
kaolin 16.6
flint 19.5
add rutile 8.3
And what's the deal with people poo-pooing rutile blues? This one is
really pretty!
Thanks for any help,
JMR
Janine Roubik on wed 9 aug 06
Hello,
Thanks for the info. Yes, what the UNT grad gave me was a photocopied handout with various sources. But John Britt found them in his book and was able to give me sp. grs. for them, which was real nice of him.
As to the more thoughtful approach, I totally agree with you, and would love to just be able to test nothing but glazes for a month or so, but the fellow who's kiln I'm using says I "test too much" and I "don't need to" with "his" glazes because he knows them like the back of his hand (MY GOD I hope so). It makes me nervous, but it's his equipment. I do have a backstock of older stuff (Cone 5 electric) that I'm taking to this gallery, but I just wanted to have some newer colors to kinda ease them in, so I don't show up with a whole batch of totally different looking stuff at some point down the road.
Thanks for all the info again! I like this listserve - people are so nice!
Janine
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Tom at Hutchtel.net on wed 9 aug 06
Janine,
Let's start from the beginning here. Specific gravity measures the ratio of
solids (ground rocks in the case of glazes) to water. The higher the
number, the more ground rock is suspended in the glaze.
Therefore, when you dip a piece into this suspension of ground rock,
(glaze), more or less will be deposited on the bisqueware depending on the
time of immersion, number of dips, drying time between dips, and maybe a
couple of other factors. So specific gravity, by itself, means
nothing....you need the bisque temperature, dipping time, and clay type to
have any potential chance of success.
This is one of the reasons that "glaze recipes don't travel well".
We usually figure that from the time we see a glaze effect we like, either
from someone else's recipe or our own concoction, it will take a minimum of
6 to 12 months to know how to dip, how to fire, how the glaze works with
other glazes we use, and, in short, have the glaze be "dependable". And we
fire 1-2 times per week.
The problem with "filling a gallery" with brand new glazes is, what happens
when someone wants another piece in that same glaze? You could spend the
rest of your life chasing something that is not duplicatable.
Are we trying to discourage you? no! But we are trying to say, committing
to a gallery full of pieces with glazes that are unknown in relationship to
your processes is full of risk and potential disappointment.
I'd really suggest going with glazes you already use, especially if you are
not in control of the firing.
Sometimes, it is best to say, "I can't do it" than to risk trying to deliver
on a commitment with unknown resources.
Tom Wirt
Hutchinson, MN
twirt@hutchtel.net
www.claycoyote.com
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