Kat Fode on wed 20 dec 00
Howdy
Ops-- Didn't give the "whole" recipe on my last posting, cause
I recieved it from a friend and wasn't sure if he wanted me to tell
everyone (you know some people can be protective) But he says
Yes go for it find out as much as possible!!! This glaze turns out
brown, with hints of blue, it is matte and gets fired to a cone 7.
Looks like a reduction glaze, but is fired in electric Ox.
Smooth matte.
Custer Feldspar 7.5
Lithium Carb. 6.0
Whiting 5.9
Titanium Dioxide 10.5
Zinc Oxide 19.5
Kaolin 19.7
Flint 30.0
-------
Add: Mang carb. 2.5
Cobalt carb. 1.5
Cobalt oxide .5
I was mostly curious about the Zinc. Lithium is a strong flux and was
wondering if somehow
this glaze was ok to use. I only use it on the outside of pots, or
peices for non-functional
ware. This recipe is way out of limits on the glaze calculation program
I use, but Lithium
is one of those difficult materials to understand.
The Curious Kat.
John Hesselberth on wed 20 dec 00
Kat Fode wrote:
>Ops-- Didn't give the "whole" recipe on my last posting, cause
>I recieved it from a friend and wasn't sure if he wanted me to tell
>everyone (you know some people can be protective) But he says
>Yes go for it find out as much as possible!!! This glaze turns out
>brown, with hints of blue, it is matte and gets fired to a cone 7.
>Looks like a reduction glaze, but is fired in electric Ox.
>Smooth matte.
>Custer Feldspar 7.5
>Lithium Carb. 6.0
>Whiting 5.9
>Titanium Dioxide 10.5
>Zinc Oxide 19.5
>Kaolin 19.7
>Flint 30.0
> -------
>Add: Mang carb. 2.5
>Cobalt carb. 1.5
>Cobalt oxide .5
Hi Kat,
You are right about it being way out of limits, but it isn't the zinc
that bothers me as much as some other things. This glaze is short of
both silica and alumina and it will be very unstable. I will bet it will
fail the vinegar test (submerge half a test coupon in vinegar for 3
days--look for color and or sheen change vs the unsubmerged portion) in
less than 3 hours, let alone 3 days. Also as Ron Roy often points out
using Lithium Carbonate as a source of lithium is not the best way to do
it. It is soluble enough that you are likely to get very uneven
distribution of it over time or maybe even on the same piece of pottery.
My HyperCard calculation of the unity formula is:
Unity Formula:
0.023 K2O 0.216 Al2O3 1.876 SiO2
0.009 Na2O 0.002 Fe2O3 0.002 TiO2
0.149 CaO 8.7:1 Si:Al Ratio
0.002 MgO
0.205 Li2O
0.613 ZnO
A stable glaze should have at least 2.5 silica and 0.25
alumina--preferably more. I wouldn't use this on functional ware (inside
or outside) unless, for some reason I don't understand, it passes the
vinegar test and shows a low level of leaching of zinc, cobalt, manganes
and lithium on a professional leach test.
If you like this glaze a lot, my recommendation would be to confine it to
sculptural pieces. If I am mistaken and it does pass vinegar and leach
testing please let me know. I am always looking to improve my
understanding and occasionally strange things do happen.
Regards, John
John Hesselberth
Frog Pond Pottery
P.O. Box 88
Pocopson, PA 19366 USA
EMail: john@frogpondpottery.com web site: http://www.frogpondpottery.com
"It is, perhaps, still necessary to say that the very best glazes cannot
conceal badly shaped pots..." David Green, Pottery Glazes
Ron Roy on wed 27 dec 00
Hi Kat,
I agree - this should not be used on food bearing surfaces.
This is seriously short of silica at cone 7 - and somewhat short of alumina
so I don't think it's a durable glaze. The other downer is the amount of
Lithium carb.
Lithium carb if present in more than small quantities (around 2%) can lead
to serious shivering in some glazes. Better test it well for fit.
It is a recrystallized zinc matte and would not function well as a liner glaze.
Lithium is not so hard to understand - it's the lithium carb that presents
special problems because it is somewhat soluble.
I would like to know how much lithium it releases when tested for leaching
if you decide to test it.
RR
>Ops-- Didn't give the "whole" recipe on my last posting, cause
>I recieved it from a friend and wasn't sure if he wanted me to tell
>everyone (you know some people can be protective) But he says
>Yes go for it find out as much as possible!!! This glaze turns out
>brown, with hints of blue, it is matte and gets fired to a cone 7.
>Looks like a reduction glaze, but is fired in electric Ox.
>Smooth matte.
>Custer Feldspar 7.5
>Lithium Carb. 6.0
>Whiting 5.9
>Titanium Dioxide 10.5
>Zinc Oxide 19.5
>Kaolin 19.7
>Flint 30.0
> -------
>Add: Mang carb. 2.5
>Cobalt carb. 1.5
>Cobalt oxide .5
>
>I was mostly curious about the Zinc. Lithium is a strong flux and was
>wondering if somehow
>this glaze was ok to use. I only use it on the outside of pots, or
>peices for non-functional
>ware. This recipe is way out of limits on the glaze calculation program
>I use, but Lithium
>is one of those difficult materials to understand.
>
>The Curious Kat.
>
>______________________________________________________________________________
>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.
Ron Roy
93 Pegasus Trail
Scarborough
Ontario, Canada
M1G 3N8
Evenings 416-439-2621
Fax 416-438-7849
| |
|
