Ivor and Olive Lewis on fri 3 mar 06
Dear Jared Webster,
The colour of a rock is no indication of the eventual colour of a glaze =
that might employ that rock as an ingredient.
You need a full analysis. Then I would suggest you consult a rather slim =
volume by an Australian Potter Ivan Englund who wrote "Rock Glazes", =
ISBN 0-95911764-0-3.
I use "Mintaro Slate" a greenish grey rock. This gives me some wonderful =
brilliant yellow crystals. But the background colour is a burnt umber.
Tailing heaps at old and ancient mines are a good places to pick up =
fragments of geological minerals which contain higher proportions of =
colouring compounds.
Have fun with your search.
Ivor Lewis.
Redhill,
South Australia.
nsmheralds@netzero.net on sat 4 mar 06
>The colour of a rock is no indication of the eventual colour of a glaze=
that =
might employ that rock as an ingredient.
I concur. I've been conducting tests using various indigenous materials=
I collected from roadsides here in Oregon. I've noted a number of mate=
rials that look quite different in raw form but will be difficult to dis=
tinguish after firing. Two samples of sandy shale from the Coast Ranges=
, one with a visibly higher iron concentration, exhibit subtle differenc=
es in color after firing. I placed, on the same test bowl, Mt. StHelens=
dacite, Mt. Hood dacite and high Cascades andesite. I was kind of lazy=
and didn't label them. After firing, they all look exactly the same. =
Oregon coastal sandstone and John Day Formation nontronitic andesite loo=
k remarkably alike and remarkably like Mt. StHelens dacite.
If you want to pursue the use of indigenous materials in ceramics, you'l=
l also want to pursue the study of geology. Looking at tables of oxide =
contents of materials is extremely helpful, but it will only give you pa=
rtial information. You need more understanding than simple oxide conten=
ts will give you if you want to more fully interpret the results of any =
test firing involving indigenous materials.
=
Nathan Miller
Thistillium Pottery
Newberg, OR
=
| |
|
