search  current discussion  categories  glazes - ash 

blak seto /was ash washing & jeff campana's posting --

updated thu 18 nov 99


Ronan ORourke on wed 17 nov 99

Thanks Hank,
that certainly made things a lot clearer. I now see the reason for the
whole process.
Gets you thinking though, what else would stay in solution when cooled
this way rather than crystallising? copper? cobalt? manganese?
I have far too much work to fit in my next firing (on Friday) as it is,
so all these tests are going to have to wait a month or so. Rest assured I
will post any interesting results.
Yes Stephen you're quite right, the only way to find out is to give it a

Thanks again for spelling things out, you certainly have wetted my
-----Original Message-----
From: Hank Murrow
Date: 11 November 1999 22:23
Subject: Re: Ash washing & Jeff Campana's posting --

----------------------------Original message----------------------------
Good Morning Steve & Ronan; A few words about Black Seto may be in
order, so bear with me. In the mid 1500s potters at the Seto kilns finally
benefited from some military trickledown and were allowed to have iron
tools made for them. Now they were finally able to pull draw trials from
their anagamas; and they were no doubt surprised to see the saturated-iron
glazes come out blackish on the drawrings instead of rusty. The iron was
trapped in the black reduced form of the oxide by the quick cooling, while
the same glazes remaining in the kiln for a normal cooling had time to
crystalize to rust colors. They soon figured out that they could increase
the iron content to get a truly deep black (which if left in the kiln would
be terribly scummed with precipitated metal) which the Tea masters loved
for its contrast with the frothy green matcha tea. Trouble was, they could
only pull a few from the stoke holes in each firing, so these wares were
relatively scarce. Of couse, by about 1600, Hideyoshi brought back potters
from Korea who introduced the new Noborigama (multi chambered) kiln design;
and long firings were out, higher temperatures were achieved, and the Shino
glazes started looking like Oribe. Arakawa ressurected the process in the
thrirties when he built his famous anagama near the site of the original
Shino kilns. Gorgeous Shino and Black Seto pieces were produced there by
Cut to the present, and your local anagama has those wonderfully
large stoke holes and you can place a tea bowl or two where you can reach
them at the end of the firing. You can take a weathered andesite (KNa .24,
Ca .44, Mg .31, Fe .26, Al .81, & Si 3.8)and add a little unwashed wood ash
(for melt & irridescence) and because it's so plastic, green glaze your
bowl or vase(for a nice crawl) and pull it out of the anagama for a quick
cool and a black glaze with some nice tong marks for decoration. Or, you
could take any Tenmoku recipe and add enough iron to more than saturate it
if left to cool in the kiln; and get a black that way. Cobalt additions
will not give the color I prize. I am describing an very thick absolutely
jet black with a sort of raven's wing irridescence, and a tortoiseshell
pattern where the crawl heals over.
And you don't need an anagama! Those who have borne with me so far
have realized that you just need a kiln with a humongous spyhole, or some
other aperture big enough to reach in and grab some pots. I have grown
impatient with the longish waits between anagama fires and the increasing
competition for that choice space near a stokehole; so I am building a
small experimental kiln which will have generous and frequent openings to
retreive pots in the way I've described. These wares don't really need an
anagama, and I need to fire them much more often if I am to produce any
good wares reliably. Hope this clarifies the former posts and whets
everyone's apetite! Hank in Eugene