julene on fri 28 mar 03
The glaze problems that you are seeing with the Blueberry Glaze is very
similar to what I saw with the Saturated Iron Glaze during my last firing.
Some unexpected pinholes and a more washed out appearance without as much
warm crystal growth that reminds me of red oaks in winter. The glaze that I
used is basically the same as yours, but with Frit 3134 instead of the
Gerstley Borate. It did not bother me considerably as I am now just setting
up my processes and controls. My pots are only fired so far as tests, my
own personal dinnerware or special gifts or charity items, so I have not had
to worry about a large number of rejects.
When the firing was almost to the point where I had planned on firing down,
I could no longer see the bottom cones. I do set the cones up to be seen,
but find looking at them through the bottom peephole in an electric kiln
difficult. Of course I was wearing safety glasses and I believe that the
the cones are needed for the control of the process. I just like having
good eyesite and find that watching/seeing the cones can be very difficult
at times. I have been collecting items needed for firing. One of which is
a high temperature thermocouple. My clay supplier was the best source that
I found for the high temperature thermocouple. They sold me the
thermocouple and 6 feet of thermocouple wire for a very good price. I
already have a multimeter. It is a simple matter of attaching the wire.
If one has the money, by all means buy what one feels is the best measuring
option and buy Lou Nils book for the TC table, as there is alot of other
useable information in there. But, as potters are probably one of the
smallest groups that uses thermocouples for temperature measurement, there
are web sources (industrial thermocouple suppliers) that have complete
charts downloadable for free from the web for most thermocouple types.
Measuring the voltage supplied by the thermocouple is a direct method of
getting this reading and very cost affective.
How accurate does one believe that high temperature measurement is anyway
and is accuracy really what you are interested in? What I would believe we
are more concerned with is repeatability. That it what I am doing setting
up repeatable processes.
After finally deciding it was time to chart the temperature of the firing,
it proved to work quite well and to be very interesting. My readings showed
that the temperature of the kiln wasn't quite at the temperatures that I
thought it was even though the heatwork was done and the cones where in the
positions that I had predetermined. The kiln also cooled much quicker than
I had thought even with the cooldown cycle. I am not saying that the
temperature that I reached was unacceptable just that it was not what I had
expected. I will now need to set up a schedule and limits to decide what is
acceptable for the results I am looking for.
I will continue to work with my processes. I am interested in knowing if
anyone else is concerned with the alkalinity of their glazes and is testing
for that? I have tried a soil tester and yes, I have found that the
alkalinity has an affect on my glazes.
Yes. I so still have the iron oxide from twenty years ago. It is a brighter
red than the present. I am just wondering if anyone else has found this
difference and if what is now called Spanish Iron Oxide is what I used to
purchase just as Red Iron Oxide.
Julene, an educated peasant, who was much more at home in the engineering
department than the art department
| |
|
