George VanOstrand on fri 2 aug 96
I have the following recipe for Rob's Red to Green cone l0:
Cornwall stone 750
Whiting 180
Colemanite 50
copper carb 100
BARIUM CARB 100
bentonite 20
There are two questions:
1. Does anyone have this recipe to check its accuracy. I'm not
sure about the COLEMANITE. In my notes there is a typographical error and
it might be DOLOMITE.
2. I can't get colemanite and it was suggested that I use Gerstley
Borate. Would this work and would the amount remain the same?
I hope someone out there with molecular analysis skills can help me.
Thanks in advance
George VanOstrand
gvanostr@julian.uwo.ca
London, Ontario
Richard Burkett on fri 2 aug 96
Regarding Rob's Green:
Your recipe, George, is identical to mine for all practical purposes. This
originated at the Kansas City Art Institute as far as I know. With all that
copper I wouldn't use it on functional ware - at least on food surfaces.
With that small of an amount of colemanite I think Gerstley borate is a safe
substitute - the version I have was written that way and often recipes
written in the past twenty years which specify colemanite really mean to
use gerstley borate, even though the two are not identical.
Richard Burkett
richard.burkett@sdsu.edu
June Perry on fri 2 aug 96
In a message dated 96-08-02 17:56:37 EDT, you write:
<< --------------------------Original message----------------------------
I have the following recipe for Rob's Red to Green cone l0:
Cornwall stone 750
Whiting 180
Colemanite 50
copper carb 100
BARIUM CARB 100
bentonite 20
There are two questions:
1. Does anyone have this recipe to check its accuracy. I'm not
sure about the COLEMANITE. In my notes there is a typographical error and
it might be DOLOMITE.
2. I can't get colemanite and it was suggested that I use Gerstley
Borat >>
I put this on the computer program and figuring it with colemanite or
gerstley or dolomite the rate of expansion showed a slight difference
favoring the colemanite. The bit of Na2O in the gerstley probably made the
difference. The gerstley lowers the Cao from .64 with the colemanite to .62,
again minute difference. I would guess that with the small amout of this
material (about 4.63% in a 100% formula which does not include the copper and
bentonite) you would be fine with any of the three choices you mention. The
little bit of boron may help with the red color. Sooooo - I would go with the
gerstley borate.
By the way, a kilogram of the glaze using the gerstley borate is $1.03 while
the same glaze using dolomite instead would lower it to .89cents per
kilogram.
Here is the molecular formula of the glaze with colemanite and without the
bentonite and copper:
..10 Na2O .34 Al2O3 2.58 SiO2
..10 K2O
..01 MgO B2O3 .14
..64 CaO
Expansion 8.01
Ratio 7.68
The bentonite will up the Silica Alumina a bit. Also using gerstley borate
instead lowers the Cao to .62, adds .03 Na2O, ups the silica to 2.60 and
lowers the B2O2 to 1.0.
Hope this helps!
June Perry
EMail: juneperry@wave.net
or: Gurushakti@aol.com
William Amsterlaw on sat 3 aug 96
To George VanOstrand:
..
On 8-2-96 you asked:
<<
1. Does anyone have this recipe to check its accuracy.
2. I can't get colemanite and it was suggested that I use Gerstley
Borate. Would this work and would the amount remain the same?
>>
..
I have the following recipe for Rob's Green posted some time ago by Dave
Eitel. It calls for Gerstley borate, not colemanite, in the same proportion
used in your recipe. It substitutes 7 parts of (non-toxic) strontium for 10
of (toxic) barium. (Dave Eitel's post indicates that he actually uses less
than 7 parts strontium with good results.) The glaze produces a glossy,
forest green.
Rob's Green
(cone 10, oxidation)
cornwall 75
whiting 18
Gerstley borate 5
copper carb 10
strontium carb 7
bentonite 2
- Bill Amsterlaw
Plattsburgh, NY
Louis Howard Katz on wed 14 aug 96
On Fri, 2 Aug 1996, Richard Burkett wrote:
> ----------------------------Original message----------------------------
> Regarding Rob's Green:
> Your recipe, George, is identical to mine for all practical purposes. This
> originated at the Kansas City Art Institute as far as I know. With all that
Some of the facts surrounding Rob's Green in my head don't quite add up.
I think the glaze got its
start when Ferguson asked
a student (Randie)to work on an
Oribe Green Sustitute known as
Randies Green I believe
Rob's was the product of a
line blend, but both my
glaze book and data base
are at another location, and the glazes are from before 1979.
Louis
***************************************************
*Louis Katz lkatz@falcon.tamucc.edu *
*Texas A&M University Corpus Christi *
*6300 Ocean Drive, Art Department *
*Corpus Christi, Tx 78412 *
*Phone (512) 994-5987 *
**************************************************
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