Gail Dapogny on fri 3 mar 00
I have two glaze questions (well, actually I have hundreds!) that I need
help with:
1. During the "orange glaze" thread recently I almost mentioned a recipe
for a frustrating cone 9-10 glaze that is gorgeous when it turns out, but
has a tendency to run badly, and also pits and sometimes blisters. I've
almost given up on it. I've always wanted to ask Ron Roy about it. The
recipe is:
custer spar 56.1
neph sye 15.4
whiting 13.3
EPK 8.6
barium carb 6.6
plus
RIO 4
titanium 8
I didn't get around to writing in, but then I saw the same recipe mentioned
by Lana Reeves who calls it ANNE SMITH ORANGE. The difference is that she
uses Kona rather than Custer. In puzzling over this, I wondered if Kona
wouldn't make it even more runny since it melts at a lower temp.... I'm
curious whether any of you have some ideas what makes this glaze so
troublesome.
2) Can anyone tell me how noticeable the difference between ordinary
custer feldspar and G200 would be? I plan to order some G200 in order to
make a temoku glaze whose recipe I noticed, but I'm curious just how great
the difference between the two would be, especially when the G200 comprises
a substantial portion of the glaze. Would this purer form of feldspar
(purer according to what I've read) give the glaze (or any glaze using
custer) less excuse to pinhole?
Thanks very much.
---Gail
Gail Dapogny
1154 Olden Road
Ann Arbor, MI 48103-3005
(734) 665-9816
gdapogny@umich.edu
www.silverhawk.com/ex99/dapogny
Nancy Guido on sat 4 mar 00
Hi Gail, I don't know who you order from but the Village Potters Guild in
Plymouth orders most of their chemicals from Rovin. They are out of stock on
the G200 and don't have plans (I'm not sure why) to get more in. We have
been using Custer in place of the G200. The only comments from Guild
members are that the matt glazes seem a little shinier. This is backwards
from what you are asking, but maybe the reverse would be true, G200 would be
a little more matt?
Nancy G.
ferenc jakab on sun 5 mar 00
Gail,
according to my database,
Custer feldspar:
K2O 10.13%
Na2O 3.03%
Al2O3 17.2%
SiO2 69.33%
Al:Si ratio 6.83
Expansion 8.06
Surface Tension 3.55
G 200 Potash Feldspar:
K2O 3.46
Na2O 3.46
Al2O3 20.86
SiO2 71.15%
Al:Si ratio 5.78
Expansion 6.53
Surface Tension 3.80
So as you can see the expansion ratio is quite different and G200 contains
considerably less potassium. I'll let the glaze gurus explain what this
means.
Feri.
Hank Murrow on sun 5 mar 00
>----------------------------Original message----------------------------
>Hi Gail, I don't know who you order from but the Village Potters Guild in
>Plymouth orders most of their chemicals from Rovin. They are out of stock on
>the G200 and don't have plans (I'm not sure why) to get more in. We have
>been using Custer in place of the G200. The only comments from Guild
>members are that the matt glazes seem a little shinier. This is backwards
>from what you are asking, but maybe the reverse would be true, G200 would be
>a little more matt?
>
>Nancy G.
Dear Gail; My experience with the two spars suggests that Custer has more
silica than G-200. Therefore, if your glazes are normally crystalline
matts, they will go shiny when they get that added SiO2. Of couse, you
might just up the fluxes a bit to compensate, a job for one of the
excellent glaze software programs we now have available. Good Luck, Hank in
Eugene
Ron Roy on mon 6 mar 00
Hi Gail,
I'm way behind so that explains why this took so long.
I need more information - are you firing in reduction? I have assumed so.
When I look at it with Custer and then with F4 I see it would tend to run
less with the F4 but have more pin holes and be more matte.
This brings up another point - I need to know what kind of clay you are
using under it and a description of your bisque firing - that might be an
explanation of the pinholes. It is unusual to have both running and pin
holes so I am suspecting unclean bisque firing.
This glaze is high in alkalies and is probably going to release some of
that barium into food - just in case your are concerned about that.
The first thing I would do with this glaze is get the Neph Sy out - it can
lead to defolocculation over time and upset the viscosity of the glaze in
the bucket - this in turn can lead to application problems - which might be
an explanation as to the different results you are getting.
Because your colour is coming from iron I would also recommend replacing
the Barium with Strontium - it works well with iron - remember. If you want
to do this just take out the Barium and replace with 5 Strontium Carb.
Let me know if you want me to design some revisions for you - RR
>----------------------------Original message----------------------------
>I have two glaze questions (well, actually I have hundreds!) that I need
>help with:
>
>1. During the "orange glaze" thread recently I almost mentioned a recipe
>for a frustrating cone 9-10 glaze that is gorgeous when it turns out, but
>has a tendency to run badly, and also pits and sometimes blisters. I've
>almost given up on it. I've always wanted to ask Ron Roy about it. The
>recipe is:
> custer spar 56.1
> neph sye 15.4
> whiting 13.3
> EPK 8.6
> barium carb 6.6
>plus
> RIO 4
> titanium 8
>
>I didn't get around to writing in, but then I saw the same recipe mentioned
>by Lana Reeves who calls it ANNE SMITH ORANGE. The difference is that she
>uses Kona rather than Custer. In puzzling over this, I wondered if Kona
>wouldn't make it even more runny since it melts at a lower temp.... I'm
>curious whether any of you have some ideas what makes this glaze so
>troublesome.
>
>
>2) Can anyone tell me how noticeable the difference between ordinary
>custer feldspar and G200 would be? I plan to order some G200 in order to
>make a temoku glaze whose recipe I noticed, but I'm curious just how great
>the difference between the two would be, especially when the G200 comprises
>a substantial portion of the glaze. Would this purer form of feldspar
>(purer according to what I've read) give the glaze (or any glaze using
>custer) less excuse to pinhole?
>
>Thanks very much.
>---Gail
Ron Roy
93 Pegasus Trail
Scarborough
Ontario, Canada
M1G 3N8
Evenings 416-439-2621
Fax 416-438-7849
Ron Roy on mon 6 mar 00
Hi Feri,
The explanation is - your data base is wrong. The Custer is close to mine
so I can't take issue with it - however - the more typical analysis for
g200 - from the mine - is
K2O - 10.67
Na2O - 3.01
CaO - 0.81
Fe2O3 - 0.08
Al2O3 - 18.41
SiO2 - 66.86
LOI - 0.16
Total 100.0
When I run that though my calculator it has a ratio of 6.17 and an
expansion of 615.57 (I use a different scale form most)
To put that in perspective the ratio for Custer is 8.85 (more silica) and
an expansion of 585.45 (cause SiO2 has a low expansion.)
the only spar like material I have data for in which the sodium and
potasium is equal is Cornwall Stone.
So tell us - where did your data come from.
>----------------------------Original message----------------------------
>Gail,
>according to my database,
>
>Custer feldspar:
>K2O 10.13%
>Na2O 3.03%
>Al2O3 17.2%
>SiO2 69.33%
>
>Al:Si ratio 6.83
>Expansion 8.06
>Surface Tension 3.55
>
>G 200 Potash Feldspar:
>K2O 3.46
>Na2O 3.46
>Al2O3 20.86
>SiO2 71.15%
>
>Al:Si ratio 5.78
>Expansion 6.53
>Surface Tension 3.80
>
>So as you can see the expansion ratio is quite different and G200 contains
>considerably less potassium. I'll let the glaze gurus explain what this
>means.
>Feri.
Ron Roy
93 Pegasus Trail
Scarborough
Ontario, Canada
M1G 3N8
Evenings 416-439-2621
Fax 416-438-7849
Ron Roy on thu 9 mar 00
Hank is right here but it depends on the ratio of the glaze to start with
and how much g200 is replaced with Custer.
If you are using a calculation program and have reasonable analysis for
your materials it would be very easy to make the substitution and make the
adjusments to the clay and/or silica.
If you are moving from Custer to G200 you will automatically lower the
ratio and keep your matte.
If you are moving from G200 to Custer there is a chance you will raise the
ratio enough to get more shine - but not always and sometimes not enough to
matter.
I know this calculation stuff seems very difficult for many of you - and it
does take some effort to learn it - but for this kind of job it is an
amazingly effective tool.
RR
>----------------------------Original message----------------------------
>Dear Gail; My experience with the two spars suggests that Custer has more
>silica than G-200. Therefore, if your glazes are normally crystalline
>matts, they will go shiny when they get that added SiO2. Of couse, you
>might just up the fluxes a bit to compensate, a job for one of the
>excellent glaze software programs we now have available.
>Good Luck, Hank in Eugene
Ron Roy
93 Pegasus Trail
Scarborough
Ontario, Canada
M1G 3N8
Evenings 416-439-2621
Fax 416-438-7849
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