Richard Mahaffey on wed 30 may 07
Bill and Matt,
I have added some more information to the previous emails.
Those pots (http://www.tacomacc.edu/home/rmahaffe/contents.htm) were
with a low iron stoneware. I think the iron content was .5 to 1%. I
usually fire below cone 01. We have kind of settled on 1850 F as a good
target. I have used saggars made of hard bricks, kiln shelves with
brick in the corners for large pieces. Thrown stoneware saggars (with
grooves and Kanthol wire to bind them), chimney flue liners. They are
going to crack anyway so we do not stress about it.
filling the saggars I use sawdust, wood chunks, bits of metal (avoid
galvanized as Zinc gas is rather poisonous) and wire and salt.
One of my students has taken to making small salt cups to hold the table
salt in different places in the saggar. We have best success if they
are either wet or bisqued. It is important to not overload the saggar
with carbon producing materials. You need to find a sweet spot where
wood products, pots and air give the best colors. I have since
switched to pine shavings that I buy in a bag from the feed store.
Very convenient, that compressed wood shavings and easy to store, too.
They sometimes call the pine "White shavings".
Another potter uses porcelain clay and adds Iron near the pots to get
the pink/peach colors. She uses iron swarth from a machine shop and
makes a kaowool tent for the pots inside the saggar. I think it is
easier to add the iron to the clay. I think that sometimes iron can
come from the fire bricks inside a saggar but I am not 100 % sure about
that. (in my experience stainless steel does not give any results).
If I were using porcelain I might think about soluble colorants on the
bisqueware to add some pop.
Terra sigs work well but are not required. I burnish my clay which is
made by a local supplier - I modified the original formula (their
formula) and I do not have the entire formula but we added some red clay
either Newman red or Carbondale red work well if you have a gray
stoneware (when wet) I would add between 5 and 10%. Either of these
makes the clay burnish nicely if you catch it at the right time.
We fire in reduction and cool rather quickly. I think the reduction
helps keep the "stuff" inside the saggar.
We use standard 50-50 epk and silica kiln putty and only seal the
saggars tops just before lighting the kiln (It seems to shrink less that
way).
If your ware is black either raise the temp (don't go above cone 01 or
cone 1 unless all else fails) or use less combustibles. I do not fill
the inside of my pots with sawdust unless I want black.
My studio phone at school is 253-566-5346 I am there between 12:30 and
3:30 M-Th or before 10:30 am in my office at 253-566-5260 if you have
any questions.
I started saggar firing in about '77 or '78 I don't do that much these
days, but I stay active because my students fire saggars fairly frequently.
Try soaking bird seed in a high concentration salt water solution - we
have gotten silver dots from that when the seeds are on top of the pot.
If you ever want someone to come and do a workshop on saggar firing let
me know, I would be happy to do that. I also have some good slides
from school trips to Turkey and China.
I hope that this helps, don't hesitate to ask questions as this is
coming off the top of my head and I kind of need to work through the
process.
Best regards,
Rick
Ps. I used to fire at cone 10 but things looked kind of burnt with some
German May wine salt glaze bottle colors so I lowered the temp to cone 6
things still looked "burnt" so I lowered the temp to cone 1 using a fire
brick saggar that was 2.5" thick. when using thinner saggars the temp
at cone 1 was too high more burnt looking ware. I read that Paul
Soldner said that in low fire Salt the lower the temperature the
brighter the color on the pots so that is what started me down the road
to low temp saggar. We just fired one at 1650 and the results were not
too good - all black with some spectacular metalic silver areas - too
much sawdust.
Pps. your saggaring may vary
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