Lili Krakowski on sat 27 sep 08
My mind is a bit boggly.
I have lived lo these many thinking that rutile in reduction can
produce a blue--without any addition of cobalt. I have assumed
that these rutile blues--which I have seen, and not particularly
liked--are celadon blues modified by the presence of titanium.
Duh.
Then there is floating blue...which we all know a lot
about....and which gets the blues from
cobalt.
Yes? No? Are we talking at cross purposes?
Duh, again.
Lili Krakowski
Be of good courage
Ivor and Olive Lewis on sun 28 sep 08
Dear Lili,
I had a look in Chappell, page 186 which gives the Floating Glaze
recipe. It contains Red Iron oxide, Cobalt oxide and Milled Rutile. It
also contains Colemanite, a rich source of Boron.
I would suggest the science of this glaze is complex. It contains two
glass forming oxides, Silicon Dioxide and Boric Oxide. Other oxides
are Soda, Potash and Lime. According to Kingery et al these modifying
oxides, especially those of the Alkali Earth Group like Calcium oxide,
influence what happens, promoting two glasses which do not mix. When
the inclusions of one glass in the other are of a favourable size
there is an optical effect. The glaze becomes opalescent and blue. In
effect, it has properties similar to those of a Chun or Jun style
glaze.
What should be expected of The Rutile content ? Under normal
circumstances this is an opacifier, so it either does not enter into
any reactions with other ingredients or it precipitates on cooling.
Why Cobalt in this recipe ? Possibly to guarantee getting a blue if
conditions are not just quite right in the kiln to deliver the desired
effect !
A good source of information relating to opalescence in glazes is
Nigel Wood,"Chinese Glazes". ISBN 90-5703-23-25.
Best regards,
Ivor Lewis.
Redhill,
South Australia.
Angela Davis on sun 28 sep 08
Mine gets boggled all the time by the exciting things I read on
this list Lili. If only I could remember half of it, I've learned to
take lots of notes.
Which is funny because the other night reading through the archives on
Floating Blue I came across a very enticing post by Steve Slatin giving a
recipe for Gnu Blue
(the same that John B posted yesterday) which is an OX rutile blue, not
reduction and no cobalt!
Worth reading here:
http://www.potters.org/subject101529.htm
I haven't mixed up any tests yet but yes this boggles my thoughts, what is
it that
I don't understand here? Is there something in the Alberta slip to
account for the blue?
The glaze sounds wonderful and I think it's a sign that it gets a mention
the day after
I "discover" it. Will mix it soon and report.
Angela Davis
In Homosassa
Have you tested this one Alisa? I didn't find it on your site, which is
the first place I check when I
find an interesting glaze. Thank you.
----- Original Message -----
From: "Lili Krakowski"
To:
Sent: Saturday, September 27, 2008 8:23 PM
Subject: Rutile blue; a question!!!
> My mind is a bit boggly.
>
> I have lived lo these many thinking that rutile in reduction can
> produce a blue--without any addition of cobalt. I have assumed
> that these rutile blues--which I have seen, and not particularly
> liked--are celadon blues modified by the presence of titanium.
> Duh.
>
> Then there is floating blue...which we all know a lot
> about....and which gets the blues from
> cobalt.
>
> Yes? No? Are we talking at cross purposes?
>
> Duh, again.
>
>
> Lili Krakowski
> Be of good courage
Steve Slatin on sun 28 sep 08
Lili -- You're not boggly at all, there're
different ways to skin a cat (or, as the
French speakers among us would say, "plumer
un canard" which I think is really great
since it translates back literally as 'pluck
a duck.')
The rutile effect in oxidation gives blue and
white, depending on the usual factors -- which
clay you put it over, thickness, maximum firing
temperature, fineness of the rutile (white specks
are more common with the coarser grades of
rutile than with the 'ceramic' grade), etc.
But if you re-fire the piece to its original
temperature (which I did to experiment with
the effects of oxide washes over an already-fired
surface) I discovered a wonderful effect in
the way of a deepening of the glaze, additional
clarity, and some hints of purple highlights.
These came at the cost of a loss in opacity/
whiteness, and the basic blue. And, of course,
some additional cracking failures in otherwise
good pots.
Since my recipe had no cobalt to be a blue
colorant, the remaining glaze was mostly
tan and glossy. Cobalt provides a dark blue
background in the Chapelle glaze where thick.
The recipe I use (which is just a modification
of the one on DigitalFire I made to accommodate
the COE/CTE of my clays; try the DigitalFire
recipe first if you're not sure, it's easy
and reliable and has ONLY THREE INGREDIENTS)
hasn't got a blue colorant and relies on the
phase change between the boron rich and
mostly silica portions of the glass to get its
color. Without the rutile, though, it's clear.
And it's just a 'vanilla' ^6 oxidation glaze.
With RIO and TiO2 to substitute, it's tan and
has no blue. Twice fired, it gets similar but
more clear. So that sort of exhausts what you
can get from me on this issue ... but I do
think that the traditional ^10 rutile blue
has no cobalt in it. I also understand that
some other ClayArters found that if
you fired with the same firing cycle, but
without reducing, you'd still get the blue.
(Which makes sense -- reduction effects
normally show up when there's an element
involved with a big color shift between
the Oxy color and the Reduc color -- copper,
iron, etc.)
So why do we associate rutile blues with
reduction? I suspect it's because they are
touchy glazes, and it's when potters are
sophisticated enough to do things like
copper reds that they master rutile blues.
Then, because the copper demands reduction
and the rutile is indifferent to atmosphere,
they fire both glazes together. (That's
entirely speculation, but there you have
it ...)
Steve Slatin --
--- On Sat, 9/27/08, Lili Krakowski wrote:
> My mind is a bit boggly.
>
> I have lived lo these many thinking that rutile in
> reduction can
> produce a blue--without any addition of cobalt. I have
> assumed
> that these rutile blues--which I have seen, and not
> particularly
> liked--are celadon blues modified by the presence of
> titanium.
> Duh.
>
> Then there is floating blue...which we all know a lot
> about....and which gets the blues from
> cobalt.
>
> Yes? No? Are we talking at cross purposes?
>
> Duh, again.
>
>
> Lili Krakowski
> Be of good courage
Ric Swenson on mon 29 sep 08
the clue to 'floating blue' is probably the colemanite. boron..... The rut=
ile is essential....but the real effect of floating blue is probably from t=
he colemanite.....in large part.
=20
=20
reactions?
=20
=20
=20
=20
=20
Ric
=20
=20
"...then fiery expedition be my wing=2C ..." -Wm. Shakespeare=2C RICHARD II=
I=2C Act IV Scene III Richard H. ("Ric") Swenson=2C Teacher=2C Office of I=
nternational Cooperation and Exchange of Jingdezhen Ceramic Institute=2C Ta=
oYang Road=2C Eastern Suburb=2C Jingdezhen City.JiangXi Province=2C P.R. of=
China. Postal code 333001. Mobile/cellular phone : 86 13767818872 < RicSwe=
nson0823@hotmail.com> http://www.jci.jx.cn/http://www.ricswenson.com
> Date: Sun=2C 28 Sep 2008 17:05:58 +0930> From: iandol@WESTNET.COM.AU> Sub=
ject: Rutile blue=3B a question!!!> To: CLAYART@LSV.CERAMICS.ORG> > Dear Li=
li=2C> I had a look in Chappell=2C page 186 which gives the Floating Glaze>=
recipe. It contains Red Iron oxide=2C Cobalt oxide and Milled Rutile. It> =
also contains Colemanite=2C a rich source of Boron.> I would suggest the sc=
ience of this glaze is complex. It contains two> glass forming oxides=2C Si=
licon Dioxide and Boric Oxide. Other oxides> are Soda=2C Potash and Lime. A=
ccording to Kingery et al these modifying> oxides=2C especially those of th=
e Alkali Earth Group like Calcium oxide=2C> influence what happens=2C promo=
ting two glasses which do not mix. When> the inclusions of one glass in the=
other are of a favourable size> there is an optical effect. The glaze beco=
mes opalescent and blue. In> effect=2C it has properties similar to those o=
f a Chun or Jun style> glaze.> What should be expected of The Rutile conten=
t ? Under normal> circumstances this is an opacifier=2C so it either does n=
ot enter into> any reactions with other ingredients or it precipitates on c=
ooling.> Why Cobalt in this recipe ? Possibly to guarantee getting a blue i=
f> conditions are not just quite right in the kiln to deliver the desired> =
effect !> A good source of information relating to opalescence in glazes is=
> Nigel Wood=2C"Chinese Glazes". ISBN 90-5703-23-25.> Best regards=2C> Ivor=
Lewis.> Redhill=2C> South Australia.
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