Paul Borian on wed 18 jun 08
For those who fire iron red glazes - at what temp to you start
reduction? I use Ohata red and the first few times I tested it out was
in an electric kiln, fired to cone 10 with a long soak, and it still
came out red. So it kind of makes me wonder just how much reduction it
really needs.
Reason I ask is that I am in the process of changing my firing schedule.
The one I use now is based around firing copper reds, which I used to do
all the time several years ago but I no longer fire them. At the time, I
found that I needed to start reduction around 1500 F in my kiln to get
them to come out and I have kept that schedule to date. My impression is
that I could wait until 1800 or 1900 F to start reducing and get the
same result - and just use a moderate reduction instead of heavy. I also
soak at top temp (cone 11) for an hour in oxidation and then drop them
temp to below the cone 9 range and hold another hour. For me, this glaze
comes out almost like a crystalline glaze - basically bright red iron
crystals floating in a rust background and I am not sure exactly why.
Thus, I am reluctant to make any major changes to the firing because I
don't want to lose this affect - but my guess is that early and heavy
reduction are not the main thing that cause it.
Any opinions?
Thanks,
Paul
John on thu 19 jun 08
Paul,
Iron reds like an oxidation atmosphere to be red.=20
In my book, " The Complete Guide to High Fire Glazes", I describe this =
and the firing cycle (02) which is oxidation to about cone 9 then light =
to medium reduction to cone 10. Then there are tons of variations from =
that. But firing with copper reds, shinos and Celadons will give you =
more of a brown color. The peak oxidation you are doing can help but =
then still tend to brown rather than red. =20
I fire Kaki's with Oil Spots, Yellows, etc.
Hope it helps,
John Britt
www.johnbrittpottery.com/wks.htm
http://ncclayclub.blogspot.com/
John Richmond on thu 19 jun 08
I have found that my best iron reds are done in an oxidation
atmosphere. Reduced atmospheres tend to make the silicate murky.
Have you tried firing your glaze in oxidation? What are the results?
John Richmond
On Jun 18, 2008, at 1:13 PM, Paul Borian wrote:
> For those who fire iron red glazes - at what temp to you start
> reduction? I use Ohata red and the first few times I tested it out was
> in an electric kiln, fired to cone 10 with a long soak, and it still
> came out red. So it kind of makes me wonder just how much reduction it
> really needs.
>
> Reason I ask is that I am in the process of changing my firing
> schedule.
> The one I use now is based around firing copper reds, which I used
> to do
> all the time several years ago but I no longer fire them. At the
> time, I
> found that I needed to start reduction around 1500 F in my kiln to get
> them to come out and I have kept that schedule to date. My
> impression is
> that I could wait until 1800 or 1900 F to start reducing and get the
> same result - and just use a moderate reduction instead of heavy. I
> also
> soak at top temp (cone 11) for an hour in oxidation and then drop them
> temp to below the cone 9 range and hold another hour. For me, this
> glaze
> comes out almost like a crystalline glaze - basically bright red iron
> crystals floating in a rust background and I am not sure exactly why.
> Thus, I am reluctant to make any major changes to the firing because I
> don't want to lose this affect - but my guess is that early and heavy
> reduction are not the main thing that cause it.
>
> Any opinions?
>
> Thanks,
>
> Paul
John Sankey on fri 20 jun 08
Here's what my experiments show:
Red iron oxide Fe2O3 decomposes to iron monoxide FeO above 1000=B0C e=
ven in
oxidising environments. Iron red is produced by a surface growth of c=
olumnar
crystals of Fe2O3, which requires oxygen. Best reds in an oxidizing
environment are obtained by a fast cool through the temperature range=
above
1000=B0C, where black FeO tends to form crystals, to about 950=B0C wh=
ere growth
of red Fe2O3 crystals is optimised. Oxygen is required for this
re-oxidization phase.
See http://sankey.ws/glazeiron.html for more details.
-----------------
Include 'Byrd' in the subject line of your reply to get through my sp=
am
filter.
I can only read text mail, no attachments.
David Hendley on mon 23 jun 08
I think glazes like Ohata do best in oxidation, not reduction.
For most potters, the truth is, we fire kiln-loads of lots of
different glazes, so you need to compromise and find what
works best for the whole load.
Pete Pinnell's column in the current Clay times is about
iron red glazes and is very interesting and well worth the read.
David Hendley
Maydelle, Texas
david(at)farmpots(dot)com
http://www.farmpots.com
>
> ----- Original Message -----
>
>
>
> For those who fire iron red glazes - at what temp to you start
> reduction? I use Ohata red and the first few times I tested it out was
> in an electric kiln, fired to cone 10 with a long soak, and it still
> came out red. So it kind of makes me wonder just how much reduction it
> really needs.
>
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