Jon Kirkendall on sun 31 jan 99
Hi all,
I've been using the following purple glaze for a while now, and it's
pretty much of a workhorse glaze: it's popular with customers, it never
runs, it has never crawled, very reliable. TOO reliable. It does not
break on high points, drips don't show, thickness doesn't change the
color. I've tried other glazes under it and it covered them right up.
I want to start playing with it because I want some slight variation in
the coloring, and am wondering where to start. Increase the gerstley
borate slightly? Add 2% bone ash? rutile? wood ash? I'm beginning to
experiment, and would love some suggestions.
Here's the glaze, cone 6, oxidation
Potash feldspar 37
gerstley borate 12
dolomite 6
talc 14
EPK 5
silica 23
zinc oxide 3
add cobalt carbonate 2
thanks, Jonathan in DC
lpskeen on mon 1 feb 99
Jon Kirkendall wrote:
> I want to start playing with it because I want some slight variation in> the c
Oh goody Jon,
Can't wait to see the responses to this, as I've had the same "problem"
with a couple of glazes I've been using - so reliable, they don't move
at all! On Tony Hansen's suggestion, I tried adding titanium, but that
dinna make it move. Rutile just sits in the bottom of the bucket and
floats around on the top of the glaze when mature. I have a box of bone
ash tho...may try that.
Good luck!
--
Lisa Skeen ICQ# 15554910
Living Tree Pottery & Soaps http://www.uncg.edu/~lpskeen
FAILURE IS NOT AN OPTION!!! It comes bundled with the software.
The Bill of Rights - (void where prohibited by law)
Brian Crocker on mon 1 feb 99
Jonathan with all the threads about Ilmanite how about it ?? Does
interesting things, spots and so on. Regards Brian
At 04:37 PM2:10: 31/01/99 EST, you wrote:
>----------------------------Original message----------------------------
>Hi all,
>
>I've been using the following purple glaze for a while now, and it's
>pretty much of a workhorse glaze: it's popular with customers, it never
>runs, it has never crawled, very reliable. TOO reliable. It does not
>break on high points, drips don't show, thickness doesn't change the
>color. I've tried other glazes under it and it covered them right up.
>
>I want to start playing with it because I want some slight variation in
>the coloring, and am wondering where to start. Increase the gerstley
>borate slightly? Add 2% bone ash? rutile? wood ash? I'm beginning to
>experiment, and would love some suggestions.
>
>Here's the glaze, cone 6, oxidation
>
>Potash feldspar 37
>gerstley borate 12
>dolomite 6
>talc 14
>EPK 5
>silica 23
>zinc oxide 3
>
>add cobalt carbonate 2
>
>thanks, Jonathan in DC
>
>
Brian Crocker
4 Erica Street,
Tea Tree Gully 5091,
South Australia,
Australia.
{e.mail} crocker@dove.com.au
"Never loose sight of the bigger picture,"
"Never loose sight of what you set out to achieve."
NAB.
Janet H Walker on mon 1 feb 99
Hi Jon. This is a great request. I've tried all kinds of unreliable
purples!! I'm sure I'm not alone!!
All are high in magnesium (you've got that part) and they have
lithium in them in some form, whether from lithium carbonate or from
spodumene. This may be to give them enough fluxing power to
counteract the magnesium (but i hesitate to add that this is idle
speculation). You could try replacing up to half of the feldspar
with spodumene just to see what happens. This is often a fun
exercise.
Your recipe matches one that Brian Kemp submitted to ClayArt awhile
ago. Brian's other mauve/purple recipes were based on chrome/tin
rather than on cobalt purple. The chrome tin amounts are usually
5.0% tin and 0.15% chrome oxide. Or you could just put your glaze
with tin in it next to your brand new thermocouple to pick up some
chrome :->
The lithium carbonate in the glazes I looked at amounted to 0.15
molecular equivalents of Li2O in the unity formula (in case you have
a glaze calc program handy). (This was about 3.5% lithium carb.)
Dunno if any of this is useful. I have a purple so powerful that it
CRACKS the POTS. Yup, this can happen! But I don't think it has to
do with the color! Prob'ly an expansion thang, right Ron?
Jan Walker
Cambridge MA USA
Ron Roy on tue 2 feb 99
Hi Jonathan,
Your glaze is oversupplied with MgO which explains why it's purple rather
than blue. Glazes with zinc oxide in them are a problem with many oxides -
chrome/ tin pinks won't work, if coloured with iron oxide you get muddy
browns. Zinc glazes work well with cobalt and copper however.
I calculated with both G200 and Custer - quite similar both ways. With
Custer the alumina goes down a bit and the silica goes up. There is barely
enough silica to match the lower limits I use and the alumina is lower than
I would recommend for a boron glaze. If you want to improve the durability
I suggest adding 10% more of either spar.
The expansion is a bit higher with the G200. Both are near what I recommend
for vitrified cone 6 bodies - but I would do a fit test to be sure.
Adding rutile is going to push the colour more to the green side and a
combination of cobalt and copper will give variations depending on the
amounts of each.
Adding zircopax will push it to more opake and the colours will be more
pastel. I suggest doing a line blend adding 2, 4, 6, 8 and 10%.
If you want to improve the durability I suggest adding 10% more spar.
If you have questions just let me know - I prefer one at a time.
RR
>----------------------------Original message----------------------------
>I've been using the following purple glaze for a while now, and it's
>pretty much of a workhorse glaze: it's popular with customers, it never
>runs, it has never crawled, very reliable. TOO reliable. It does not
>break on high points, drips don't show, thickness doesn't change the
>color. I've tried other glazes under it and it covered them right up.
>I want to start playing with it because I want some slight variation in
>the coloring, and am wondering where to start. Increase the gerstley
>borate slightly? Add 2% bone ash? rutile? wood ash? I'm beginning to
>experiment, and would love some suggestions.
>Here's the glaze, cone 6, oxidation
>Potash feldspar 37
>gerstley borate 12
>dolomite 6
>talc 14
>EPK 5
>silica 23
>zinc oxide 3
>add cobalt carbonate 2
Ron Roy
93 Pegasus Trail
Scarborough, Ontario
Canada M1G 3N8
Tel: 416-439-2621
Fax: 416-438-7849
Web page: http://digitalfire.com/education/people/ronroy.htm
Jon Kirkendall on wed 3 feb 99
Thanks for your response, Ron. One question (for now!): what role does
the small amount of zinc oxide play in this glaze? Is it used as a
flux? The glaze, again, is:
>
>Potash feldspar 37
>gerstley borate 12
>dolomite 6
>talc 14
>EPK 5
>silica 23
>zinc oxide 3
>
>add cobalt carbonate 2
I've always had trouble with zinc and would just as soon leave it out.
Jonathan
Chris Schafale on thu 4 feb 99
Jonathan --
Here's an idea for variegating your purple glaze. I'll say at the
outset that it is untried by me, and I have no idea if it
will work. I was given a recipe for a wash that can be brushed,
sprayed or sponged over another glaze to produce some glaze
movement/interesting effects. All it consists of is: 150 g Gerstley
Borate, 20 g rutile, and 5 g titanium, mixed with water to a
skim-milk consistency. You can also use different colorants, such as
30 g copper carb, 5 g. cobalt carb, or 30 g red iron oxide, instead
of the rutile/titanium.
Let me know if you try it and what the results are.
Chris
Light One Candle Pottery
Fuquay-Varina, NC
candle@nuteknet.com
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