Lynne Antone on sun 29 oct 06
Somehow my last message got sent while I was still typing, sorry. That's what happens when you have to take your eyes off of the screen and look for where the numbers are ;-) Now to finish and shorten up a bit:
I am doing some glaze tests today and tomorrow and wanted to try to get a
Transparent Purple glaze to pick up stamping and incising on my pots. I have a
nice purple already, but it is opaque and mostly covers up all of my design
work. In my purple glaze I use Tin Oxide and Green Chrome Oxide along with
Cobalt Carb. to get the purple color. I think I understand that the Tin is an
opacifier and suspect that the Green Chrome is also. And I was told that Tin makes Green Chrome turn pink or the other way around, but still you get pink with the combo.
The two bases that I plan to use contain Custer Feldspar, Gerst. Borate, Whiting, EPK and Silica and the other is the Glossy Clear Liner Glaze from "Mastering Cone 6 Glazes" containing G-200 Feld, Ferro Frit 3134, Wollastonite, EPK, Talc and Silica. I can post all the numbers if you want, I thought I'd just do the ingredients so you could tell me in any are also opacifiers. I just can not get this glaze mixing and combining down in my head. I have read the book twice at different times, tried to read Lili's instructions and I guess I am too dense to get it.
What else can I use, besides a Mason Stain, to get a glossy, clear purple?
Thanks all,
Lynne Antone
--
"Whenever I feel blue, I just start breathing again"
Beaver Creek Arts
Olympia WA
USA
Steve Slatin on mon 30 oct 06
Lynne -- You've got several different issues here, all wrapped up in the
single question ... how to get a clear purple glaze.
As you develop more knowledge, pieces of the glaze puzzle will
start to fall into place. There are multiple issues -- how you fire,
the other things in a glaze load, the components of the glaze,
the clay you use ... and what goes on inside of a glaze during
the melting stage of a firing is, at best, poorly understood.
The basic outline of a glaze -- bones, flesh, blood; glass
formers, stiffeners, and fluxes -- is an oversimplification.
Learning how things differ takes time -- how reducing a glaze
by a percent or two in sodium and increasing by a corresponding
amount of magnesium -- will still make a glaze, but with
different expansion characteristics. Lowering a few percent
in potassium and increasing calcium by the same amount
again usually gives you a workable glaze, but will be less
glossy and perhaps more opaque. Keeping the fluxes the
same and changing the silica to alumina ratio will change
the surface and flow of a glaze.
So my first thought is, don't be discouraged. This is something
many folks find difficult.
My second thought is this -- purples are great sellers, they
are quite striking, and lots of potters want a good purple in
their stable. But purple is problematic -- there really isn't any
such thing as purple light. The colors of light are red, orange,
yellow, green, blue, indigo, and violet. Yellow is a 'real'
color, a color of light. Purple is created with a mixture of
red and blue, and the deep, rich shade that many potters
prize is particularly dependent on reflected light. But you
want a transparent glaze, not an opaque, so this makes
things a little more difficult. What this comes down to
is that you'll have to play quite a bit with these things to
get what you want, it won't be easy, and you may find that
you can't get what SHOULD work to actually get there
because of some small thing relating to the clay you use,
the firing cycle, interactions between the melters and
the colorants, or something else like that.
The third thought I have on this is that because you're
firing in oxidation looking for a red and blue combination
will be a problem. You're probably going to have to go with
a tin-chrome red. (The blue is easy; many clear glazes
plus cobalt turn blue.) The principal opacifiers I'm aware of
are zircon (and its oxides and silicate), rutile, titanium dioxide,
and tin. Getting to the red in the base works against your
goal of getting to clear.
So now we're at the stage of looking for alternatives that
will give purple. Some of the purples I've seen have
had manganese in the glaze. (Manganese gives the lovely
purple color to amythyst.) But there's a bad history of
manganese toxicity among potters, so I don't recommend it.
Four thoughts, still no actual progress. Don't be discouraged!
It's usually this way, sometimes worse.
My fifth thought is this -- cobalt oxides (& carbonates, in
glaze recipes) don't always give a 'true' blue. It's quite
soluble in glaze melts, so it's not opacifying. Staying as close
to cobalt alone will also make keeping the glaze transparent
easier.
In glazes based mostly on sodium, calcium, and potassium as
melters, cobalt tends to be just plain blue. If the glaze has moderate
in magnesium, you tend to get mostly lilac, but sometimes
violet. Glazes with barium (or strontium) as a melter give a
vivid, interesting blue-green. With high magnesium, violet,
purple, and lavender are possible, but high magnesium tends
to create a matte surface. Matte surfaces are inherently more
opaque than smooth surfaces.
So ... sixth though. What you need is a high magnesium
glaze that's pretty smooth and clear, to which you can add
something between a half a percent and two percent of cobalt
to get some response that will be clear and in the purple
range. If you can find a very transparent clear high-magnesium
glaze, that could be the answer. I don't know of such a glaze,
though, so I toss one more idea.
This gets us to #7 -- I've had some small patches of
purple appear on some test tiles, rather unpredictably,
from what should be matte glazes that have been 'juiced'
with a little lithium to get them into the moderately glossy
range. Bailey gives a recipe -- check his book for T-14,
one of many 'transparent cone 6 base glaze' recipes he
has -- and try it with something in the region of 1 - 2
percent cobalt. This may suit your needs, but it may
not be as strongly purple as you wish. Send me a note
if you don't have access to Bailey's book and need the
recipe.
Of course the beauty to stains is that they don't change
in the glaze -- the colors remain true. If you aren't comfortable
with glaze formulation, and have found a recipe for a good,
reliable clear glaze, just adding a purple stain does make
some sense.
Regarding your two proposed glazes, Glossy Clear Liner
is, in fact, glossy and clear -- I've found some fit problems
with it and don't use it any more, but John H has reformulated
it for other potters with the same problem, and has something
on his web site about it, IIRC. He's always been extremely
generous with his time and experience.
The other glaze looks like a clear, though whether it's
truly transparent or not will depend on the proportions.
Have you read Lili Krakowski's basic glaze calc course
postings? I found them to be clear and direct -- and
fairly simple. Vicki Hardin posted them on her site
at http://vickihardin.com/articles/glaze-course/lili-krakowski.html
-- but they really concentrate on how to calculate a glaze
and presume you already have an understanding of what
a glaze is and how it works.
My background included a tiny bit of chemistry when I
started doing glazes, and I was able to read and understand
Rhodes on the subject. Since then everything else has
been relatively easy (except for Kingery -- I'd not recommend
Kingery unless you have a good 'hard science' background
and are really interested in materials engineering, in which
case you've probably already read it).
There are many ways to get started on this journey. You
may decide you just want to take other folks' glazes and
mix them up and see if they work -- I do a fair bit of that
myself. You may want to push a glaze around to get it to
do what you want -- that takes more knowledge, but you
can develop it well enough with a few simple experiments.
Best wishes -- Steve Slatin
--------------------------------------------------------
Somehow my last message got sent while I was still typing, sorry. That's what happens when you have to take your eyes off of the screen and look for where the numbers are ;-) Now to finish and shorten up a bit:
I am doing some glaze tests today and tomorrow and wanted to try to get a
Transparent Purple glaze to pick up stamping and incising on my pots. I have a
nice purple already, but it is opaque and mostly covers up all of my design
work. In my purple glaze I use Tin Oxide and Green Chrome Oxide along with
Cobalt Carb. to get the purple color. I think I understand that the Tin is an
opacifier and suspect that the Green Chrome is also. And I was told that Tin makes Green Chrome turn pink or the other way around, but still you get pink with the combo.
The two bases that I plan to use contain Custer Feldspar, Gerst. Borate, Whiting, EPK and Silica and the other is the Glossy Clear Liner Glaze from "Mastering Cone 6 Glazes" containing G-200 Feld, Ferro Frit 3134, Wollastonite, EPK, Talc and Silica. I can post all the numbers if you want, I thought I'd just do the ingredients so you could tell me in any are also opacifiers. I just can not get this glaze mixing and combining down in my head. I have read the book twice at different times, tried to read Lili's instructions and I guess I am too dense to get it.
What else can I use, besides a Mason Stain, to get a glossy, clear purple?
Thanks all,
Lynne Antone
Steve Slatin --
They grew and grew up the old church wall
Till they could growe no higher
They lapped and tyed in a true love knot
The rose wrapped ‘round the briar”
---------------------------------
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Ron Roy on mon 30 oct 06
Hi Lynne,
Removing some clay (EPK) will make a glaze more glossy and more transparent
- do several tests lowering the EPK by one each time.
Removing alumina (clay is mostly alumina and silica) can also cause a glaze
to run so fire your tests on some thing that will protect your shelves.
RR
>Somehow my last message got sent while I was still typing, sorry. That's
>what happens when you have to take your eyes off of the screen and look
>for where the numbers are ;-) Now to finish and shorten up a bit:
>
>I am doing some glaze tests today and tomorrow and wanted to try to get a
>Transparent Purple glaze to pick up stamping and incising on my pots. I have a
>nice purple already, but it is opaque and mostly covers up all of my design
>work. In my purple glaze I use Tin Oxide and Green Chrome Oxide along with
>Cobalt Carb. to get the purple color. I think I understand that the Tin is an
>opacifier and suspect that the Green Chrome is also. And I was told that
>Tin makes Green Chrome turn pink or the other way around, but still you
>get pink with the combo.
>
>The two bases that I plan to use contain Custer Feldspar, Gerst. Borate,
>Whiting, EPK and Silica and the other is the Glossy Clear Liner Glaze from
>"Mastering Cone 6 Glazes" containing G-200 Feld, Ferro Frit 3134,
>Wollastonite, EPK, Talc and Silica. I can post all the numbers if you
>want, I thought I'd just do the ingredients so you could tell me in any
>are also opacifiers. I just can not get this glaze mixing and combining
>down in my head. I have read the book twice at different times, tried to
>read Lili's instructions and I guess I am too dense to get it.
>
>What else can I use, besides a Mason Stain, to get a glossy, clear purple?
>
>Thanks all,
>
>Lynne Antone
Ron Roy
RR#4
15084 Little Lake Road
Brighton, Ontario
Canada
K0K 1H0
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