Paul Herman on thu 7 apr 05
Hi D. Michael,
I'm so glad to have had the right guess!
I've used that combination for many years, but with ash from Utah
Juniper rather than Ponderosa. The Juniper variation produces a dry
cracked surface, more of a sintered slip than a glaze. But it does get
that nice yellow color.
As for the difference between the California Ponderosa ash and the
Colorado varety, I'm not surprised. They are after all very different
places, and the geology/mineralogy would certainly affect the trees that
grow there.
Another consideration is what part of the tree the ash comes from. Bark,
small branches and twigs are reputed to contain more traces of metal
oxides, hence more color.
We have recently been trying to put these ideas into practice with our
woodfirings. In the previous firing (October '04) we burned a
predominance of truss scraps. It was industrial wood, mostly Douglas
Fir. We all thought the colors on the work were less intense than
previous firings, and considered that we had burned less bark and
branches.
So this spring's firing (finished last night and down to 1200F after 24
hours) we burned several barrels of Ponderosa bark that had accumulated
around the splitter, and a lot of limb wood. We also stretched out the
total wood stoking another eight hours, to 72. There is a lot riding on
these twice yearly firings, and sunday morning seems like a long time to
wait.
good (fine) ashey firings,
Paul Herman
Great Basin Pottery
Doyle, California US
http://www.greatbasinpottery.com/
----------
>From: DMCARTS@AOL.COM
>To: CLAYART@LSV.CERAMICS.ORG
>Subject: Re: =A0 =A0 =A0 Re: Shino and Ash Glaze Answer
>Date: Thu, Apr 7, 2005, 6:27 AM
>
> Thanks to all who took a shot at a guess of the two ingredients in the dr=
y
> Yellow glaze....Believe it or not the ingredients are 50 EPK and 50 Ponde=
rosa
> Pine Ash (unwashed), that's it! (on stoneware) Paul Herman had the best g=
uess
> with Ash and Kaolin.
>
> I have fired this glaze before (in L.A.) and it came out brown to Mauve
> Brown. Here In Pagosa Springs, CO I get this great yellow. I'm sure its t=
he
> soil
> contributing to the ash but not sure exactly. I've been told that the ran=
chers
> around here claim that the grasses here are the highest is minerals,
beneficial
> to cattle, than any other place in Colorado....maybe something to that.
>
> Any ideas?...Do you think this is unusual or am I easily impressed?
>
> D. Michael Coffee
Jim Murphy on thu 7 apr 05
on 4/7/05 8:27 AM, DMCARTS@AOL.COM at DMCARTS@AOL.COM wrote:
> I have fired this glaze before (in L.A.) and it came out brown to Mauve
> Brown. Here In Pagosa Springs, CO I get this great yellow. I'm sure its the
> soil ...
> Any ideas?...Do you think this is unusual or am I easily impressed?
Hi Dennis,
It makes sense at higher altitude - since water tends to run "downhill" -
soil of higher mineral concentration would be left at the top of a
hill/mountain.
There's also something about alkaline soils (pH above 7.0) causing iron
deficiencies in plant growth. In Ponderosa Pine, the "needles" turn
yellowish when soil is Iron-deficient.
A question remains though, is there more or less Iron in high-altitude
woodash ?
Perhaps, growth in Iron-deficient soil - at higher altitude - may account
for your different glaze results (L.A. vs. Colorado).
Best wishes,
Jim Murphy
| |
|
