Wanda Holmes on wed 3 apr 02
In continuing to research this problem, I did an internet search on bristol
glazes. I came up with the following reference in an article by John Fromme
to something called Satin-vellum glazes on:
http://art.sdsu.edu/ceramicsweb/articles/glaze_tech/fluxes_silica_alumina.ht
ml
"Satin-vellum glazes
Satin-vellum glazes often contain zinc oxide as an ingredient.
Since true matt glazes often tend to have rough surfaces which
are easily marked by metal and which are difficult to clean,
the satin-vellum glazes provide a functional alternative. The
much smoother semi-matt surface of the satin-vellum glazes
have a most attractive satin sheen surface and are produced by
the addition of 3 to 4% zinc, titanium and tin oxides in a
majolica or low-earthenware region (1100 C. (2110 F.)."
This description of the surface fits the original glaze and my revised one
perfectly. It's what I love and want to keep, while eliminating the
leaching problem, if possible. Does anyone know more about these
satin-vellum glazes?
Wanda
-----Original Message-----
From: Ceramic Arts Discussion List [mailto:CLAYART@LSV.CERAMICS.ORG]On
Behalf Of John Hesselberth
Sent: Monday, April 01, 2002 8:17 PM
To: CLAYART@LSV.CERAMICS.ORG
Subject: Re: Glaze gurus, I could use your help REVISED
Hi Wanda,
This glaze has some unusual characteristics and is outside the range of what
I have tested so I am speculating to some degree. You say it is a waxy
semi-matte, yet it has a silica/alumina ratio of over 10. This would
clearly be in the glossy range so I speculate that you are not getting it
melted (rule 3). Of course it also violates Rules 1 and 2 as you noted.
Notice that it has very little K/Na, some calcium and lots of zinc. Yes
zinc is a good flux at cone 6, but not as good as K/Na.
When you then raised the Si and Al levels to meet minimum rule 1 and 2 goals
you made it even more difficult to melt. The little bit of boron you added
was probably not enough to get the job done--so you are still having a
problem with rule 3. If you took this glaze up to cone 8 - 10 it might do
better--that is the easiest way to see if it is a melting problem. Of
course the glaze will probably be glossy then.
So bottom line--my guess is that this is a good example of an unmelted
matte--and a great new example for me to add to my bag of
lemon-juice-test-tiles. Who else will hazard a guess?
Regards,
John
on 4/1/02 8:11 PM, Wanda Holmes at wholmes@FORTETECHNOLOGY.COM wrote:
> I forgot to give the unity value for B2O3 in the revised glaze. It is
.08.
> Wanda
>
> -----Original Message-----
> From: Wanda Holmes [mailto:wholmes@fortetechnology.com]
> Sent: Monday, April 01, 2002 7:06 PM
> To: Clayart
> Subject: Glaze gurus, I could use your help
>
>
> I tested Richard Behren's Satin Matt Cone 6 glaze and fell in love with
the
> waxy semi-matte surface. However, it leached badly in a 3-day vinegar
test.
> So, I set about to make it more durable. Despite my efforts, the
"improved"
> glaze still leaches almost as badly. Any insight any of you can offer
would
> be most appreciated.
>
> The original recipe was:
> Feldspar (I used Custer) 34.9
> Whiting 12.62
> Zinc oxide 25.8
> EPK 4.10
> Silica 22.6
>
> .5 Cobalt carbonate added
>
> The chemical formula is:
> Na2O .03
> K2O .08
> MgO .00
> CaO .25
> ZnO .64
>
> Al2O3 .15
>
> SiO2 1.6
> P2O5 .00
> TiO2 .00
> Fe2O3 .00
>
> Al:Si 1:10.92
>
> My improved recipe is:
> Custer feldspar 25.8
> Whiting 5.2
> Zinc Oxide 18.6
> EPK 9.3
> Silica 26.7
> Ferro Frit 3124
> Cobalt carbonate .5
>
> With a chemical formula of:
> Na2O .07
> K2O .08
> MgO .00
> CaO .24
> ZnO .61
>
> Al2O3 .25
>
> SiO2 2.52
> P2O5 .00
> TiO2 .00
> Fe2O3 .00
>
> Al:Si 1:10.28
>
> My strategy was to get it within the limits set out by Ron & John in
> "Mastering Cone 6 Glazes", boost the alumina and silica up into the
durable
> range, keep the Al:Si ratio near the original values, & keep the fluxes
near
> their original values.
>
> The surface quality of the new glaze is very like the original. The color
> response is a bit less intense. Once again, it is a thing of beauty, but
> not durable. Should I just keep boosting up the Al & Si until I find a
> durable result or ruin the surface quality, whichever comes first?
>
> Wanda
____________________________________________________________________________
__
Send postings to clayart@lsv.ceramics.org
You may look at the archives for the list or change your subscription
settings from http://www.ceramics.org/clayart/
Moderator of the list is Mel Jacobson who may be reached at
melpots@pclink.com.
| |
|
