bill edwards on fri 1 apr 05
Here's the way to do the tests for colorants. The base
should be calculated without colorant if you want to
check for accuracy. The colorant is added in addition
to the base and if you are looking to round that off
to 100 you will re-calculate once you reach the
desired mark. Most glaze calculations programs can do
either one or you will have to use a hand held
calculator and average the materials. Its easier to
monitor the base seperate from the colorants so you
can adjust the colorant loads without tampering with
the original base while doing a study on color.
Remember, many bases can take various colorants, some
do not hold certain oxides well at high loads and
thats when you would start looking for factors that
can effect the ability of the base to release metal
oxides. The addition on an over-load would throw some
of the vital materials that make the base stable into
a newer set of percentages possible going out of range
for heat work you would use as well as its ability to
remain stable.
Once you start doing this you can use the lemon or
lime test method Ron and Jon has explained to see if
leaching occurs. Bases need to be checked for a myriad
of things to ensure a good start and any addition of
color needs to be re-calculated for performance.
There's lots of dynamics at play between the weights
of specific colorants added to various bases. What you
done was allot of work but you learn valuable
experience from those efforts. Keep doing it and
learning!
You would weigh the 1% addition and add that to your
total base glaze weight and continue doing that until
you find your favorite area based on your fired test
results. (I cheat and do a low, medium and high mix
for oxides and then look for the middle grounds upon
testing) If the low weight of an expected colorant
doesn't hit the area I expected then I have a
mid-range area and an over-load area where I can go
back and make comparisons) Then you can modify the
base if you have to in order for it to remain stable
for whatever purpose you need. Lots of possibilities
within glazing using a
few bases and coloring oxides. Keep in mind you may
have a re-test effort on your hands in the base won't
hold its colors and you have to modify but it can be
done. This is why we see in here the many attempts to
correctly get the proper information out but sometimes
its a squabble over how it should be done since it
does take hands on experience and some calculations
experience. The less toxic material used, the better.
The less leaching you get, the better. But you don't
want cracked pots of poor glazes so there's lots of
curves in learning this. Also the hot to cold/cold to
hot transition on your test tiles once you find the
color level you like might be an option. Look for
micro breaks in the glaze or do a ink rub on them
after a few freeze thaws in boiling water.
I am late is seeing this and Ron or Jon may have
already taken you up on this? Anyways, good luck and
happy testing. Let us know you results!
Not all glazes are for food bearing purposes and
sometimes that gets lost in the threads when a glaze
shows up. There are some that wouldn't work at all for
that but others would choose them for other types of
art. The argument is weather or not these would hold
up to the test of time. That argument is void since
some circumstances prove that in art, some materials
that are used simply are not suitable for food bearing
surfaces due to their toxic potential. All dust is
hazardous and fumes should be avoided in firing. I
would like to start seeing recipes that go public with
an end use purpose designation but thats not going to
happen in my life time. It is getting better however
thanks to many out there who have worked for years to
see that potters around the World are getting the best
solutions possible using science and common sense and
understanding thermal dynamics.
I have glazes that I wrote that are lab tested by
outside sources. I do this as insurance even though I
know from my own testing before I send the product out
how it should perform. I once owned a business
that manfactured art colorants and you learn from
these experiences and believe me those learning curves
were rather expensive at the time. There's some I use
for decorative
use thats not toxic in short term understanding and
knowledge but I wouldn't use them for cooking or
eating out of. Lead or Cadmium are never used in my
work nor is barium or even lithium. I wouldn't use
these materials in
my past art colorants nor would I now but I don't shun
those who do with exception to lead and cadmium with
special emphasis added towards lead where we do have
good record of damages pertaining to this substance
over a long period of time. Commercially
some of these are still on the market. Thats a choice
for them because they have in house labs. I think Ron
and Jon have proven you can really get more out of
your glazes and kilns than you could have ever
imagined and many people are beginning to see this.
All glazes can be essentially made better, and if not,
we don't need them. Even those artsy type colorants I
mentioned can be made better. Crawl glazes have even
came up to snuff in the arts world over the years
using different technology to get there. I wouldn't
want to try and eat off them however. The idea of a
knife scraping across those bumps doesn't appeal to me
in the least. Lol
The main purpose and intent is being able to enjoy
what you do and do it as safe as possible, extending
that safety margin out as far and wide as possible.
Clayart is loaded with this information already under
various mentions and it is advisable to continue
re-shaping your thoughts and testing to accompany the
trends and shifts in technology and the market. This
meaning, we do have to repeat ourselves periodically
and push our art to the next level. In the last 2-3
years there has been a complete over-haul in the minds
of many using the Mastering ^6 glazes and other well
written books. I believe more now than ever many have
learned that it takes less recipes than in the past to
get twice as much from your work. Simplicity and
creative use of heat and colorants known for safety
have added greatly to our business as potters and
artists and the achievements have been astonishing.
There's much, much more we can do now and we do need
to continue talking about it. We also can continue
posting (open) recipes here and their end purposes and
continue learning how to make them better, safer and
in some cases, cheaper without compromise to the
product.
The GB debate sill rages on and there's pro/con's
related to its use. Its one of Earths natural forming
materials that isn't known for stability in lab
testing due to changes in make-up or rather where its
dug. I still have great pieces of pottery that has
seen the oven and dinner table for nearly 10 years
using GB as the major component in the mix. The
products are also in great shape and time tested. But
there's newer technology where I have removed all GB
from my materials and can in most cases come within
95% of the work I done in the past with GB. I really
love this work and I believe with all my heart that
everyone has really built our business as potters to a
level never seen in the past. This has been good for
all involved!
I will never relent that I have learned all I need to
know. I want more and more information in front of me
than ever before.
Bill Edwards
Edmar Studio and Gallery
My question is..... after 19 dips you are no longer
using a 500 gram
batch. Each dip leaves a little less of the base
glaze so the
proportion of oxide to base glaze is different. Is
this correct?? I
recently did this with copper carb. only with 3
additions of 1/4
percent each but I mixed up three different batches so
that the
proportion would be accurate. Did I waste my time? I
thought of doing
it the way Kate did, but chickened out, thinking it
wouldn't be an
accurate test of the color. Mike Gordon
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Ron Roy on mon 4 apr 05
We should keep in mind that all glazes leach - it is a matter of how much
and under what conditions.
The lemon test only shows up very unstable glazes - if you want to know if
your glazes are stable have them lab tested and apply the standards you
think are appropriate and/or that are imposed by law.
I am tempted to say - you can avoid all that by not using know toxic
materials in your liner glaze. The trouble with that advice is the lack of
real thought that most potters have about what is toxic and what is not.
RR
>Once you start doing this you can use the lemon or
>lime test method Ron and Jon has explained to see if
>leaching occurs. Bases need to be checked for a myriad
>of things to ensure a good start and any addition of
>color needs to be re-calculated for performance.
>There's lots of dynamics at play between the weights
>of specific colorants added to various bases. What you
>done was allot of work but you learn valuable
>experience from those efforts. Keep doing it and
>learning!
Ron Roy
RR#4
15084 Little Lake Road
Brighton, Ontario
Canada
K0K 1H0
Phone: 613-475-9544
Fax: 613-475-3513
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