MudFire - Luba & Erik on fri 14 oct 05
I have used these two cone 10 reduction glazes for a long time and love them
dearly. They are the softest of mattes and most beautifully variegated,
delicious to hold glazes in our studio. But with gas prices going through
the roof, I'm testing lots of cone 6 reduction glazes to hopefully change
over in the next year or so. These two glazes I just can't let go but I
don't know enough about glaze conversion yet to tackle these on my own.
Could any of the glaze gurus please help me take a stab at converting these
cone 10 redux glazes to cone 6 redux? Thank you so much!!!
MARKET BLUE
Custer Feldspar 50
Whiting 4
EPK 24
Dolomite 22
Cobalt Carbonate 0.5
AUTUMN YELLOW
Soda Feldspar 43.4
EPK 20.8
Dolomite 13.9
Whiting 8.7
Tin Oxide 4.3
Bone Ash 6.9
Bentonite 2
Red Iron Oxide 0.5
Luba
MudFire Clayworks and Pottery Center
Open Studio * Gallery * Workshops
www.mudfire.com
175 Laredo Drive
Decatur, GA 30030
404-377-8033
Daniel Semler on sat 15 oct 05
Hi Luba,
I had a quick (well actually not so quick but there you go:)) look at this.
I have previously taken a clay matte not unlike Autumn Yellow from Cone 10
Redux to Cone 6 redux. Did this for a w/s with RR. Anyhow did a line blend
between the base glaze with about 5% boron added and 10% boron added. Turned
out 5% was enough and by the time you got to 10 there was a greenish tinge
showing up. It wasn't a perfect match for surface but it was very close.
Tried a similar trick with yours. Trouble is finding a frit that does not
introduce more silica. You have so little in this glaze that its a bit of a
problem. But try a 5 part blend of these two and see what it looks like.
So the first one has about 4% or a bit less Boron. Note also that its
expansion
has dropped a little. Not a problem in this case I wouldn't think.
Autumn Yellow (4% Boron) Autumn Yellow (8% Boron)
Code Number: Luba Code Number: Luba
====================================
=========================================
F4 SPAR................ 33.70 F4 SPAR.....................
21.80
DOLOMITE............... 13.90 DOLOMITE....................
11.20
WHITING................ 6.30 WHITING.....................
7.00
BONE ASH............... 6.50 BONE ASH....................
5.60
EPK.................... 19.40 EPK.........................
20.00
TIN.................... 4.30 TIN.........................
4.40
BENTONITE.............. 1.90 BENTONITE...................
1.60
F3195.................. 14.00 F3195.......................
28.30
=========
=========
100.00
99.90
A couple of notes. I left the bentonite in the 100% as you supplied
it and its
relative percentage has dropped, but with all that clay you probably never
needed it anyway. I corrected the tin so that percentage wise its still about
what it was in the original. In most cases I would have expected both the
bentonite and the tin to be additional to a base glaze of 100%. Note the 99.90
in the 8% case is simply a computer rounding affect.
The expansion in both these glazes is appreciably lower than the original.
Matte glaze expansion is however not well predicted by calc. software
so I tend
not to worry. It is interesting to note how similar this exercise was to my
other glaze. The same COE drop in calculations was noted. Further, the fluxes
start to deviate a little in the 8% boron case as there simply is too little
room for movement in a glaze of this composition, at least for me. There just
isn't enough silica to make changes easy to absorb.
Finally, the frit I chose is 3195, mainly 'cos its what I used last time. If
you don't have this frit I can try with another if you let me know what you
have. But bear in mind that I looked at a few and they just didn't make a good
choice and things were rather harder.
One final thing. In doing a 5 part blend with these two glazes I would expect
that you'll find something close in the left most two based on what I saw. If
you end up using the ones further to the 8% boron glaze you'll note that there
is a ton of clay. Perhaps it will crawl, not sure.
Oh, and remember to add in 0.5 % iron which I just left out of my calcs for
simplicity's sake.
Market Blue changes :
Market Blue (4.6% boron) Market Blue (7.3% boron)
Code Number: Luba Code Number: Luba
====================================
=========================================
CUSTER SPAR............ 37.60 CUSTER SPAR.................
30.20
DOLOMITE............... 22.20 DOLOMITE....................
20.10
EPK.................... 23.10 EPK.........................
22.60
F3195.................. 17.10 F3195.......................
27.10
=========
=========
100.00
100.00
Again, with these line blend them in 5 parts and check out what which works.
Here the adjusted glazes are better matches for the original
molecularly due to
the higher silica. Again, expansions are lower and again for clay mattes its
probably irrelevant. I dropped the whiting in the end because we had
enough CaO
from the frit. Also remember to add the cobalt carb. 0.5% in each
recipe. Again
it makes no difference to the calcs so I left it out.
Let me know how this goes also.
If you questions about the above let me know. If you are doing glaze calc
yourself and want more details on how I did this let me know and I'll give as
much as I can. I have tried to explain with this some of the problems. Your
biggest one here is the lack of silica. The boron quantity was chosen so that
it fell well inside the limits for cone 6 glazes. I suggest a blend
test of two
glazes so that you can see what happens with the boron additions. It
will affect
the iron for example.
HTH
D
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