Janet Starr on mon 1 jan 07
I have also found that adding colorants reduces crazing. I asked this
question to Ron Roy at a workshop and he did not have a specific answer.
Since "Mastering Cone 6 Glazes" and the "Glazemaster" calculation program
(and all the other calculation programs) treat colorants as extras, there
doesn't seem to be a way to measure the effect of oxides on a glaze. I am
also interested in finding out about anyone's results in this area. It
seems that we are leaving out a whole area of glaze chemistry. I'd like to
see one of the programs include the effects of colorants on the glaze. Does
anyone have any experience with this?
Over time I have noticed a pattern when I test clear bases with coloring
Base glazes that craze on my clay body, can appear with no crazing when
coloring oxides are added.
In most cases, percents of 5-10 RIO or 1-2 Cobalt will show un crazed. I
have not studied these surfaces under
a microscope, but they are clearly improved surfaces when looking at them in
sunlight. An example of this is the last colorant tests I made,
using Brian Gartside's Volume Clear Glaze. The clear was badly crazed, but
all the tiles, colored with RIO and Cobalt, were not crazed.
However, since the base was crazed, I feel nervous about the seemingly un
crazed tiles. I mean, maybe they are crazed, but I do not see it.
Or, like shivering can much later, perhaps crazing can also happen much
I have used this base now in a bigger batch with 10 RIO, and the pots are
not crazed, as I can see. In fact, the glaze is looks like a lush Tenmoku
at Cone 6.
Contrary to this improvement, I have seen Copper Oxide as a colorant, make
an un crazed clear glaze,
I would like to study this closer. Is there any documentation on the above?
Suggestions for glaze testing to
further investigate this? Do coloring oxides have an effect on expansion of
a glaze? Maybe a big yes, and this is an
area I in the dark about, or, it could be something interesting to study.
After the weekend, I am starting up again and would like to look into this
relationship, if there is one.
These evenings I have reread all of the articles I thought where interesting
in my year of Clay Times and Pottery Illustrated.
I think the columns in Clay Times have excellent information that one can
benefit from reading a few times.
Best regards from Alisa in Denmark
claystevslat on tue 2 jan 07
I can't speak to 'all' programs, but Glaze Master
certainly does allow you to include colorants in
the COE calculation.
All you have to do is to put them in the
same spaces where the regular ingredients go,
instead of down at the bottom.
Putting the colorants and the suspension agents
into the calculation gives you a significantly
improved understanding of your glaze.
-- Steve Slatin
--- In email@example.com, Janet Starr wrote:
> Hi Alisa,
> I have also found that adding colorants reduces crazing. I asked
> question to Ron Roy at a workshop and he did not have a specific
> Since "Mastering Cone 6 Glazes" and the "Glazemaster" calculation
> (and all the other calculation programs) treat colorants as
> doesn't seem to be a way to measure the effect of oxides on a