John Baymore on tue 13 may 97
--------------------------------------------------------------------------
........... Scrap Black-ecologists special
Keep a wash bucket for all your throwaway and cleanup. All dumped glaze
tests at all temps from raku to high-fire, clay washed off your hands,
glaze
wiped off the bottom of pots, leftover glazes and tests you didn't like,
etc.
...........
Dump a bunch of oxides in it till it is really black. Iron chromate is
cheap, use it first. Then more iron, some manganese, and about 1% cobalt.
Gotta have the cobalt or it won't be really black. Test it till it's
really
good. .......
---------------------------------------------------------------------------
---
This is a great way to use up scrap glaze........... beats polluting the
world .
However, I would not use this stuff on the food contact surfaces of
functional pieces. The "dump in coloring oxides until it is saturated and
turns black" approach to coloration is NOT a good one for particularly food
safe glazes. Particularly with the manganese and chromium components.
You also have to be sure that things like lead and cadmium haven't been
washed off into this "unknown" glaze formula. In school situations or
"coop" studios this is a REAL possibility since you really don't know what
and all is in use by every single person in the studio. Commercial low
fire glazes, china paints, overglaze enamels, underglazes, lusters, and the
like can get in there too! Someone may have just decided to dump
........."that bag noone knows what is in"......... just to finally get rid
of it !
BTW, ........... iron chromate is listed as a carcinogen, as are all
chromium compounds. It is cheap.....but be careful handling it.
Enjoy these "found" scrap glazes for what they are....... they are often
beautiful and "once in a lifetime" discoveries.
Also BTW...... if you fire ^10 reduction:
Go outside. Scoop up a container of dirt (not humus). Mix it with 2
containers of unwashed wood ashes. Wet seive through 80-100 m seive.
(Careful....it's caustic.) Discard what stays on the seive. Apply
resulting glaze, medium to thin, onto bisque pot and fire. (Place first
test on on a "cookie" in the kiln in case it runs.) See what you get.
Works in all places I have tried it. Adjust ash to dirt proportions for
other possible glazes.
Unless you scoop up the dirt from a Superfund Site or the trees burned
were growing on top of the tailings pile for a uranium mine , it
probably doesn't contain anything very toxic in a high enough concentration
to be of concern in a food contact sense, however it probably is not a well
balanced glass...... may be pretty "soft". Mostly it will probably contain
CaO, Na2O, K2O, MgO, Al2O3, SiO2, Fe2O3, and a trace of TiO2 and P2O5.
Likely it will craze, so if that bothers you as to hygiene, experiment and
add commercial flint to adjust fit.
Best,
........................john
John Baymore
River Bend Pottery
22 Riverbend Way
Wilton, NH 03086
603-654-2752
JBaymore@Compuserve.com
| |
|
