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ron roy's cone 6 black liner glaze

updated wed 5 nov 08


James F on tue 4 nov 08

I use Ron's wonderful and trouble-free black liner glaze from MC6G quite ex=
tensively. I used it on the Identity piece=2C but as some of you may have =
noticed=2C it tends to break to golden brown on the high spots=2C which in =
this piece is rather distracting. I discussed with Ron a few of my ideas f=
or altering the glaze to reduce breaking=2C and he added a few of his own i=
deas. We decided that the results of the test should be posted to the list=
in case there are others who might find this line of research beneficial. =
Please note that I do not know what effect my alteration has on the food s=
afety of the glaze. I do not think there will be any adverse effect=2C but=
proceed at your own risk. In any case=2C here are my results:


I just pulled from the kiln my experiments with altering your black liner g=
laze to eliminate breaking=2C and thought you might like to know the result=
s. All were fired to a hard cone 6 using the following ramp:

570 degrees F per hour to 1982. 200 per hour to 2232=2C with a 10 minute s=
oak. Natural cooling down to 1900. 150 per hour to 1500=2C then natural c=
ooling to room temperature.

I tested four of the ideas by performing line blends=2C adding more EPK=2C =
cutting back the frit=2C adding tin=2C and adding zircon.

Adding EPK did not reduce the breaking. Even with an extra 10%=2C the glaz=
e broke as before. The extra EPK did=2C however=2C affect the glaze color=
=2C dulling it noticeably and imparting a distinct gunmetal tinge=2C even a=
t just 2% additional.

The next experiment was with cutting back the frit. There was no change in=
breaking until I had cut back to 20% from the original 26%. The breaking =
was completely eliminated when cut to 16%. The color remained a rich black=
=2C and the glaze appeared mature and glossy in all cases.

The experiments with adding tin were unsatisfactory. While breaking was el=
iminated at 4% and higher tin=2C the color of the glaze was decidedly brown=

The experiments with adding zircon were also unsatisfactory. 8% and higher=
Zr did eliminate the breaking but the glaze again went brown=2C though les=
s so than with the tin.

I think I am going to go with the reduced frit version (18% rather than 26)=
. It is obviously fine for sculptural work=2C but wonder what you think fr=
om a functional standpoint?

Thanks for your advice and guidance.


James Freeman

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