Anne Doyle on tue 19 jun 07
Hi everyone!
I'm sooooo glad this is back up and running, i realized while clayart was
off-line just how isolated i am up here with no ceramics friends to
consult and i really missed reading what you guys and gals all have to
say...
Anyhoo, here's the thing i need advice on:
I did a whole series of colour tests with MC6 bases for about 2 months
awhile back and developped the colours i wanted for my textured pieces. In
one particular case, I settled on a colour and decided to move forward
with it. Tested 100gm batch, then a 400gm batch and it was great, right
colour, right finish, no pinholes...
This was Glossy Base 1 with the addition of 0.35 chrome oxide and 1.0 zinc
oxide. On the test tiles done in my small test kiln it came out a
beautiful sage green.
I had a minor mishap... ok, maybe more than minor. As i was mixing the
10,000gm batch, some of the powder spilled out on the floor. I swept (I
know!) it up gently and tried to save as much of it as i could but who
knows how much of which powder i really lost. I didn't think it was that
much really.
So, i glazed up 20+ pieces in this colour and fired them to ^6...
The pieces came out beige, with maybe a very faint hint of green but not
more than that. A few pinholes here and there,...
I told myself, forget it and just make up a new batch, but i thought i'd
do some tests first. I tested the beige from the bucket with an added 2%
of each of the following: G-200, also with 3134(for added boron), then
with EPK, and also one with all 3 to see... well, tiles came out sage
green...?... in fact i ran a test tile of the original batch and it came
out green as well, although not as nice as the tests with the added %
s... ???
So, i'm left wondering if my test kiln is actually an oxidation atmosphere
(there are no peepholes and no venting), and maybe in the big kiln with
peepholes open the chrome is just vanishing? I'm not sure i'm explaining
this right... i wonder if my test kiln is really producing different
results because its a different atmosphere? Is that possible? It's a 115v
electric test kiln that was once used for annealing i think, or glasswork
anyhow... has a peephole in the front i use for watching the cones but it
doesn't really stay open during firing, it has a little metal piece that
falls back over the hole...
Anyhow, is it possible that i can't get the greens i'm getting in the test
kiln in the big kiln for this reason?
I look forward to reading your response as i am more than a bit stumped by
this...
"it is a puzzlement"
Thanx,
Anne
Paul Lewing on fri 22 jun 07
On Jun 19, 2007, at 8:17 AM, Anne Doyle wrote:
This was Glossy Base 1 with the addition of 0.35 chrome oxide and 1.0
zinc
oxide. On the test tiles done in my small test kiln it came out a
beautiful sage green.
Anne, your problem here is the interaction of the chrome with the
zinc. I think the reason you are encountering the variability is
that you have very little of either and so it takes only some tiny
variation somewhere to make it go green or brown. I'd say if you
want it more reliably green, cut the zinc. If you want it to be
brown all the time, add more zinc.
A more reliable way to get the same color might be to use iron
chromate as a colorant, in a base that has no zinc.
Paul Lewing
www.paullewingtile.com
John and Judy Hesselberth on fri 22 jun 07
On Jun 19, 2007, at 11:17 AM, Anne Doyle wrote:
> Anyhow, is it possible that i can't get the greens i'm getting in
> the test
> kiln in the big kiln for this reason?
>
> I look forward to reading your response as i am more than a bit
> stumped by
> this...
> "it is a puzzlement"
>
> Thanx,
> Anne
Hi Anne,
Two thoughts come to mind. First a major difference between test
kilns and larger kilns is often cooling rate. Unless you are firing
your test kiln down to match the cooling rate of your big kiln you
will get different results and that can include different colors as
well as different degrees of glossiness of matteness.
Second you may have dispersed the colorant better in the small batch
than in the large. This can happen easily if you let a batch sit a
few days and then don't thoroughly redisperse. I also do it by
pouring the batch through a sieve so I can see that the bottom of the
bucket is clean before I reuse a glaze.
Regards,
John
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