Liz Dodge on thu 23 oct 97
Bonnie and I have been having a little off-list discussion about this maroon
glaze called Kemp 17. Its come up before on this list, but its time to
elevate this to the experts - Ron Roy or others and share with all again.
Why is this chrome 6 oxidation glaze containing chrome a lovely maroon
color?
---------------------------------------------------------------------
Previous discussion:
Liz,
I guess it's a chrome glaze in a boron base. boron from Gerstley Borate,
but there is so little chrome in it! I've heard that in a glaze firing,
if there are ANY glazes with chrome they will turn ANY glazes with boron
pink, so maybe that's why there is so little chrome-- not any more
needed. Did you post Ron Roy on this?
Bonnie D. Hellman
Pittsburgh, PA
work email: oliviatcavy@juno.com
home email: mou10man@sgi.net
On Mon, 20 Oct 1997 10:02:47 oliviatcavy writes:
>
>From: Liz Dodge
>To: Multiple recipients of list CLAYART
>Subject: Re: Request for translucent maroon cone 6 (oxidation) recipe
>Date: Fri, 17 Oct 1997 10:31:37 EDT
>Message-ID: <199710171742.NAAAA25260@x6.boston.juno.com>
>
>----------------------------Original
>message----------------------------
>This glaze has been discussed on clayart previously. Its a really
>nice gloss
>cone 6 oxidation maroon/dark red (despite the description). Darker
>where
>thick, breaks to white where thin.
>
>Kemp 17 Red/Pink/Purple/Mauve
>
>Ingredient Percentage
>
>Nepheline Syenite 16
>Whiting 20
>Gerstley Borate 21
>Kaolin 11
>Silica 32
>Tin Oxide 5
>Chrome oxide 0.15
>
>
>Liz Dodge
>Berkeley, CA
>
>--------- End forwarded message ----------
---------------------
Forwarded message:
From: oliviatcavy@juno.com
To: LizzardOL@aol.com
Date: 97-10-20 13:38:58 EDT
Liz,
I guess it's a chrome glaze in a boron base. boron from Gerstley Borate,
but there is so little chrome in it! I've heard that in a glaze firing,
if there are ANY glazes with chrome they will turn ANY glazes with boron
pink, so maybe that's why there is so little chrome-- not any more
needed. Did you post Ron Roy on this?
Bonnie D. Hellman
Pittsburgh, PA
work email: oliviatcavy@juno.com
home email: mou10man@sgi.net
On Mon, 20 Oct 1997 10:02:47 oliviatcavy writes:
>
>From: Liz Dodge
>To: Multiple recipients of list CLAYART
>Subject: Re: Request for translucent maroon cone 6 (oxidation) recipe
>Date: Fri, 17 Oct 1997 10:31:37 EDT
>Message-ID: <199710171742.NAAAA25260@x6.boston.juno.com>
>
>----------------------------Original
>message----------------------------
>This glaze has been discussed on clayart previously. Its a really
>nice gloss
>cone 6 oxidation maroon/dark red (despite the description). Darker
>where
>thick, breaks to white where thin.
>
>Kemp 17 Red/Pink/Purple/Mauve
>
>Ingredient Percentage
>
>Nepheline Syenite 16
>Whiting 20
>Gerstley Borate 21
>Kaolin 11
>Silica 32
>Tin Oxide 5
>Chrome oxide 0.15
>
>
>Liz Dodge
>Berkeley, CA
>
>--------- End forwarded message ----------
Ron Roy on sat 25 oct 97
Hi Bonnie and Liz,
What I know is what I read on this.
First of all the red comes from the combination of Tin and Chrome - called
chrome-tin red. The amounts of each are within the recommended limits for
this type of glaze. The chrome can vary from under 0.1 to up around 0.5.
The amount of chrome and the chrome/tin ratio give different shades from
pink, red, maroon, purple and green but these are not the only factors.
This type of glaze depends on a certain percent of CaO - best to keep that
percent over 12 - this glaze has 17.25 - a lot - in fact oversupplied for a
cone 6 glaze. Because Gerstley Borate is the source of boron for this glaze
there is some MgO present ( 1.10 percent.) This may account for the
discrepancy in reported colour because MgO will vary in the Gerstley
Borate.
The glaze is short of silica for cone 6 and the alumina is on the low side.
Some one once said on ClayArt that boron would prevent this kind of colour
response - not so - but not having enough CaO would. I have even read that
the more boron you have the more CaO you need to counteract the solvent
action of the B2O3.
If you wanted more consistent colour results (if the colour varies from
load to load) you should raise the alumina and silica in this glaze.
Don't try to get this colour with any glaze containing Zinc.
>----------------------------Original message----------------------------
>Bonnie and I have been having a little off-list discussion about this maroon
>glaze called Kemp 17. Its come up before on this list, but its time to
>elevate this to the experts - Ron Roy or others and share with all again.
> Why is this chrome 6 oxidation glaze containing chrome a lovely maroon
>color?
>
>>This glaze has been discussed on clayart previously. Its a really
>>nice gloss
>>cone 6 oxidation maroon/dark red (despite the description). Darker
>>where
>>thick, breaks to white where thin.
>>
>>Kemp 17 Red/Pink/Purple/Mauve
>>
>>Ingredient Percentage
>>
>>Nepheline Syenite 16
>>Whiting 20
>>Gerstley Borate 21
>>Kaolin 11
>>Silica 32
>>Tin Oxide 5
>>Chrome oxide 0.15
Ron Roy
93 Pegasus Trail
Scarborough,Canada
M1G 3N8
Evenings, call 416 439 2621
Fax, 416 438 7849
Studio: 416-752-7862.
Email ronroy@astral.magic.ca
Home page http://digitalfire.com/education/people/ronroy.htm
KEMPB on sat 25 oct 97
Hi everyone,
I am the original sender of the now infamous Kemp 17
which seems to have taken on a life of it's own. I cannot claim
that it is "my" glaze because like most glazes, we get them from
various sources and adapt them to our particular needs.
Now it is my understanding - and experience - that a combination of
tin and chromium in a ratio of around 20:1, will give you colours
in the pink/mauve range, depending on the base glaze.......when
fired in an oxidation atmosphere.
The boron in the glaze or in surrounding glazes is not the culprit
when it comes to flashings of pink on other pots. It is the tin in
other glazes that is the problem.
Referring to The Potter's Dictionary of Materials and Techniques,
Frank Hamer writes " at this temperature (1200 degrees C - 2192
degrees F) the chromium oxide becomes volatile and some will travel
to adjacent pots in the kiln. It is impossible to keep other tin
glazed pots from becoming flazhed with pink. The original glaze
does not seem to be thereby depleted in colour."
So, have fun and keep on keeping on !!!!
Brian Kemp
PS. I am a boomerang freak. I design, make and throw boomerangs and
one of the famous boomerangs is coincidentally a Kemp 17.
It was designed by an American (Lorin Hawes) who lives in
Australia. He gave it the name Kemp 17 because it had a wing span
of 17 inches and he made it and test flew it at Kemp Beach in
Queensland Australia. (I understand that it was not pink in colour
!!!!)
kempb@nievax.nie.ac.sg
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