lili krakowski on thu 23 jul 09
Lis writes: " ...I really want to know... what substance will affect =3D
the
colour of cobalt in the way I want. I know adding red iron oxide will =3D
make
it greyer, and adding copper or chrome or green stain will make it =3D
greener
and red stain purpler..... but there has to be something simple that =3D
makes
the blue of cobalt dark, rich, cool and 'earthy'. Even if it was the =3D
clay
body, what in the clay had that effect?"
What's to say? You want something perfectly reasonable. But clay is =3D
NOT reasonable.
It is as varied and capricious as nature itself.
I know I am going to be long-winded and boring, but bare with me (as the =
=3D
stripper said)
and I will try to make this "Archives clear."
Sorry your slip recipe was thrown out. House cleaning ALWAYS is=3D20
a mistake leading to catastrophe! But your slip was a slip, there
are no "mytery" or "surprise" ones--all that can happen is that the =3D
proportions of this clay
to that clay, this flux to that flux, is different. Theoretically your =3D
slip recipe called
for materials no longer available--so ou'd be stuck anyway.
Permit me to take all this apart.
You CANNOT know that Fe2O3 will make the glaze greyer. Nor can you be =3D
sure
that adding this or that will have this "guaranteed, money back" result.
As I tried to explain earlier you are looking through glass when you =3D
look at a glaze.
It is as though you were looking through sunglasses. Through sunglasses =
=3D
your scrambled
eggs look olive colored, your ketchup disgusting, the whole wheat toast =3D
dark grey...And the milk
green or similar. When you look AT most glazes you are looking THROUGH =3D
most glazes
and you will have different "impressions" depending on the glass itself, =
=3D
how thick
it is, and so on...how mature the glaze is...and what shows through from =
=3D
the clay.
The clay body affects the glaze in at least two possible ways. First, =3D
materials IN the
clay will melt into the glaze, interact with it, affecting its color. =3D
So magnesium in the body
will affect the cobalt in your glaze. The texture of the clay body can =3D
affect the
look of the glaze, simply because roughness of the body would affect=3D20
the structure of the glaze surface. =3D20
And now we get to slip. Slip in this case is simply an interface. It =3D
"negates" the effects
of the body, replacing them with its own.
You might try Bonnie Staffel's black slip--85% Barnard, 15% whiting. If =
=3D
you have
no Barnard, Ron Roy designed a synthetic one...Check Archives.
You say you are using a white body you like. Use a white slip that =3D
has
no magnesium (in case clay body does) to test.
TINT your slip with some cobalt, and other possibilities--nickel, =3D
rutile, chrome*,=3D20
chrome* + copper, manganese*, and see what happens.
Try for a heavily tinted slip, with no tinting, and very little tinting =
=3D
in your glaze
All you can know is that, given a certain glaze recipe, certain results =3D
are likely to occur.
I do not know if I whined yet that my computer ate all its content up =3D
the other day, so I
have to re-do my Glaze Master (TM) . I must ask John if and how one can =
=3D
save all one's
recipes on disk. (I digress, sorry)
IF your cobalt is in a high magnesium glaze, or over a talc containing =3D
body (talc is magnesium
silicate), and a frightening number of white clay bodies at lower temps =
=3D
are magnesium containing,
you will get purple. Nice purple, ugly purple. Purple. =3D20
IF you are using a ferrugineous body or one with manganese* your blue =3D
will be somewhat muddied.
It will not be that great Delft blue we know and love (Esp. in Delf).
If your cobalt is in a highly alkaline glaze: much potash, sodium, =3D
lithium, or woodash, it should be
a pleasant blue...with some difference between potash and soda I never =3D
remember which does what
but not that much.
If you are using a high calcium glaze there will be little effect. =3D
Nothing special. And if
at mid-range or below you are using a calcium borate glaze--likely if =3D
you use a frit--the boron
will have slight effect...it will just be blue.
You still have not told us what glaze you are using. Maybe you should =3D
try another glaze
with different ingredients. Some very pretty blues emerge in zinc =3D
containing glazes. Give'em a whirl!
However.
If this were my problem I would start with a look at my glaze. What =3D
glaze family does it belong to?
I then would test the other glaze families....that means, yes, one with =3D
magnesium also. I would test at leastone with zinc,
which has its own reactions with colors. (A box full of "u"s will be =3D
provided for those who use British spelling.)
I would try all the galzes I am testing with tin, also with Zirconium. =3D2=
0
I would try slips over the body, and pigments over the glaze.
Lovely Derek Emms Pigment:
Red Clay 92
Cobalt oxide or carbonate 4
Mn2O3 4*
Can be used as a slip
David Eeles colorant:
Talc 12.50
Kaolin 25
R ed Art Clay 18.75
Cobalt Cab 25
Manganese 12.50
Red Iron Ox.25
Here is a Jenny Lykins c6-11 slip
Grolleg 50=3D20
Custer Spar 25
Flint 25
Bentonite 2.
With 10% rutile it is honey, with 1/2% cobalt it is blue.
Cardew has a blue stain which I have used and do use.
Cobalt 20
Manganese 10
Tin 20
Po spar 30
Silica 20
Fluorspar 20
This is Katherine Scott's Blue Grey "pigment." My guess it that added =3D
cobalt would bring a dark blue
Fe2O3 25
Cobalt 15
Manganese 10
Chrome 5
Gerstely Borate 10
This was used at c.10 or so, so extra flux may be needed. No idea.
Black Engobe (no idea of source)
Wollastonite 42
Frit 3110 or P283 (NOT equivalent, two different frits)15
Bentonite B 30
Cobalt 3
Iron Oxide 10
Conrad Blue (I assume from his book)
China clay 72
Cobalt Oxide 15
Chrome 13 *
The * after manganese and chrome are to point out to Newbies that these =
=3D
materials have "warnings" attached, and they should take the proper =3D
precautions re: toxic materials. Look'em up, do as told.
Same caution applies to Iron Chromate a very interesting but unloved =3D
material, great, I think, for simply darkening colors.
In fine (thank goodness) I would try slips and pigments under =3D
transparent, semi-trans plain glaze, or tinted glaze. I would try each =3D
slip/pigment under each glaze--going from lightly tinted to heavily =3D
tinted glaze.
I might try the slips and pigments under a clear alkaline, a calcium =3D
borate, a zinc ontaining glaze that is clear, has some cobalt, more =3D
cobalt. Do same with clear glazes . And try your clear glazes with a =3D
small amount of tin, and a small amount of zirconium (two separate =3D
tests.)
And lettuce know what happens.
lili krakowski on thu 23 jul 09
Lis writes: " ...I really want to know... what substance will affect =3D
the
colour of cobalt in the way I want. I know adding red iron oxide will =3D
make
it greyer, and adding copper or chrome or green stain will make it =3D
greener
and red stain purpler..... but there has to be something simple that =3D
makes
the blue of cobalt dark, rich, cool and 'earthy'. Even if it was the =3D
clay
body, what in the clay had that effect?"
What's to say? You want something perfectly reasonable. But clay is =3D
NOT reasonable.
It is as varied and carpicious as nature itself.
I know I am going to be long-winded and boring, but bare with me (as the =
=3D
stripper said)
and I will try to make this what I like to call "Archives clear."
I am sorry that your slip recipe was thrown out. I would not worry =3D
about it. The slip was a slip, there
are no "mytery" or "surprise" ones--all that can happen is that the =3D
proportions of this clay
to that clay, this flux to that flux, is differnt. Theoreticall your =3D
slip recipe called
for materials no longer available.
Permit me to take this all apart.
You CANNOT know that Fe2O3 will make the glaze greyer. Nor can you be =3D
sure
that adding this or that will have this "guaranteed, money back" result.
As I tried to explain earlier you are looking through glass when you =3D
look at a glaze.
It is as though you were looking through sunglasses. Through sunglasses =
=3D
your scrambled
eggs look olive colored, your ketchup disgusting, the whole wheat toast =3D
dark grey...And the milk
green or similar. When you look AT most glazes you are looking THROUGH =3D
most glazes
and you will have different "impressions" depending on the glass itself, =
=3D
how thick
it is, and so on...how mature the glaze is...and what shows through from =
=3D
the clay.
The clay body affects the glaze in two possible ways. First materials =3D
IN the
clay will melt into the glaze, interact with it, affecting its color. =3D
So magnesium in the body
will affect the cobalt in your glaze. The texture of the clay body can =3D
affect the
look of the glaze, simply because roughness of the body would affect=3D20
the structure of the glaze surface. =3D20
And now we get to slip. Slip in this case is simply and interface. It =3D
"negates" the effecs
of the body, replacing them with its own.
You might try Bonnie Staffel's black slip--85% Barnard, 15% whiting. If =
=3D
you have
no Barnard, Ron Roy designed a synthetic one...
As you say you are using a white body that you like, use a white slip =3D
that has
no magnesium (in case clay body does)
TINT your slip with some cobalt, and other possibilities--nickel, =3D
rutile, chrome,=3D20
chrome + coppet, manganese*, and see what happens.
Try in fact for a heavily tinted slip, with very little tinting in your =3D
glaze
All you can know is that given a certain glaze recipe certain results =3D
are likely to occur.
I do not know if I whined yet that my computer ate all its content up =3D
the other day, so I
have to re-do my Glaze Master (TM) . I must ask John if and how one can =
=3D
save all one's
recipes on disk. (I digress, sorry)
IF your cobalt is in a high magnesium glaze, or over a talc containing =3D
body (talc is magnesium
silicate) and a frightening number of white clay bodies at lower temps =3D
are magnesium containing)
you will get purple. Nice purple, ugly purple. Purple. =3D20
IF you are using a ferrugineous body or one with manganese your blue =3D
will be somewhat muddied.
It will not be that great Delft blue we know and love (Esp. in Delf).
If your cobalt is in a highly alkaline glaze: much potash, sodium, =3D
lithium, or woodash, it should be
a pleasant blue...with some difference between potash and soda I never =3D
remember which does what
but not that much.
If you are using a high calcium glaze there will be little effect. =3D
Nothing special. And if
at mid-range or below you are using a calcium borate glaze--likely if =3D
you use a frit--the boron
will have slight effect...it will just be blue.
You still have not told us what glaze you are using. Maybe you should =3D
try another glaze
with different ingredients. =3D20
However.
If this were my problem I would start with a look at my glaze. What =3D
glaze family does it belong to?
I then would test the other glaze families....that means, yes, one with =3D
magnesium also. I would test one with zinc,
which has its own reactions with colors. (A box full of "u"s will be =3D
provided for those who use British spelling.)
I would try slips over the body, and pigments over as well as under the =3D
glaze.
Lovely Derek Emms Pigment:
Red Clay 92
Cobalt oxide or carbonate 4
Mn2O3 4*
Can be used as a slip
David Eeles colorant:
Talc 12.50
Kaolin 25
R ed Art Clay 18.75
Cobalt Cab 25
Manganese 12.50
Red Iron Ox .25
Here is a Jenny Lykins c6-11 slip
Grolleg 50=3D20
Custer Spar 25
Flint 25
Bentonite 2.
With 10% rutile it is honey, with 1/2% cobalt it is blue.
Cardew has a blue stain which I have used and do use.
Cobalt 20
Manganese* 10
Tin 20
Pot spar 30
Silica 20
Fluorspar 20
This is Katherine Scott's Blue Grey "pigment." My guess it that added =3D
cobalt would bring a dark blue
Fe2O3 25
Cobalt 15
Manganese 10
Chrome 5*=3D20
Gerstley Borate 10
This was used at c.10 or so, so extra flux may be needed. No idea.
Black Engobe (no idea of source)
Wollastonite 42
Frit 3110 or P283 (NOT equivalent, two different frits) 15
Bentonite B 30
Cobalt 3
Iron Oxide 10
Conrad Blue (i assume from his book)
China clay 72
Cobalt Oxide 15
Chrome 13 *
The * after manganese and chrome are there to point out to Newbies that =3D
these materials have "warnings" attached, and they should take the =3D
proper precautions re: toxic materials. Look'em up, do as told.
Same caution applies to Iron Chromate a very interesting but unloved =3D
material, great, I think, simply darkening colors.
In fine (thank goodness) I would try slips and pigments under =3D
transparent, semi-trans plain glaze, or tinted glaze.
And lettuce know what happens.
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