Judy Rohrbaugh on fri 17 feb 06
I have never seen floating blue, just read about it here on clayart.
I made, well, rather, stumbled upon a glaze that sounds similar to what you all write
about and I don't mind sharing if someone wants it.. I only ask that you let me know if you get anywhere.
I have fired it on a buff/light reddish clay and have gotten the best results. I have done tests on this but none lately and I don't have all of the notes as far as what I have used in colorant amounts.
I just mixed up a batch to try over white clay. It fired ok, (whew) but the color is sort of washed out. I used 2% cobalt carb and 2% rio. There is some rutile, too, I would have to look up the amouunt, it is small, maybe 2% or so.
These are the notes I no longer have: I had used this glaze before over the buff/red and got a nice mottled plum brown that broke into some mottled blue.
Would anyone have any idea of what amounts of rio and cobalt to use? The rutile was the same, I am certain.
Also a way to get a nicer, deeper blue- but not a blue jean color blue. That seems to be what I got today, with some lighter mottling.
I recall trying 4% cobalt carb and 1 or 2% rio and the blue was a stark blue jean color.
So, for this last firing, anyway, I think I am getting the right firing range, it was cone 6 hard on the bottom row of my kiln, where these pots were- and cone 5 at the top of my kiln where other pots were.
Do you fire your floating blue over white clay or a color? This glaze does not work at all over my speckled clay (manganese).
Judy Rohrbaugh
Fine Art Stoneware
Ohio
Steve Slatin on fri 17 feb 06
Judy --
There are many different floating blue recipes, and most are different
over different clays. One of the few generally accepted commonalities
is that a floating blue glaze has a phase separation that actually
causes the 'hare's fur' effect and some or all of the blue.
The floating blue I use has no cobalt in it, and the blue is entirely
a result of the phase separation effect.
If you take a strong colorant (like cobalt oxide or cobalt
carbonate) and use 4% in the glaze, you'll get blue like
crazy, but not a 'floating' blue -- because the colorant
will make the entire glaze, top to bottom, blue. The
phase separation, a light blue effect, will be invisible over
-- and under -- the dark blue colorant. In short, too much
blue, no float. Also, 4% cobalt has a substantial flux effect.
If you've got a glaze that vitrifies well without it, I'd be
concerned with running at that concentration.
I'd recommend raising the rutile amount before raising the cobalt.
Ref: http://ceramic-materials.com/cermat/education/17.html
(Good article on Floating Blue)
http://ceramic-materials.com/cermat/education/17.html
(Zamek's article on substituting for gerstley borate, his
recipe uses 1% cobalt and 4% rutile, with 2% spanish RIO
Best wishes, and tell us about your results -- Steve Slatin
Judy Rohrbaugh wrote:
I have never seen floating blue, just read about it here on clayart.
I made, well, rather, stumbled upon a glaze that sounds similar to what you all write
about and I don't mind sharing if someone wants it.. I only ask that you let me know if you get anywhere.
I have fired it on a buff/light reddish clay and have gotten the best results. I have done tests on this but none lately and I don't have all of the notes as far as what I have used in colorant amounts.
I just mixed up a batch to try over white clay. It fired ok, (whew) but the color is sort of washed out. I used 2% cobalt carb and 2% rio. There is some rutile, too, I would have to look up the amouunt, it is small, maybe 2% or so.
These are the notes I no longer have: I had used this glaze before over the buff/red and got a nice mottled plum brown that broke into some mottled blue.
Would anyone have any idea of what amounts of rio and cobalt to use? The rutile was the same, I am certain.
Also a way to get a nicer, deeper blue- but not a blue jean color blue. That seems to be what I got today, with some lighter mottling.
I recall trying 4% cobalt carb and 1 or 2% rio and the blue was a stark blue jean color.
So, for this last firing, anyway, I think I am getting the right firing range, it was cone 6 hard on the bottom row of my kiln, where these pots were- and cone 5 at the top of my kiln where other pots were.
Do you fire your floating blue over white clay or a color? This glaze does not work at all over my speckled clay (manganese).
Judy Rohrbaugh
Fine Art Stoneware
Ohio
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Don Goodrich on fri 17 feb 06
Hi Judy,
I agree with Steve that 4% cobalt is too much. I use about 1.5 percent
cobalt carbonate in my Floating Blue.
You can see some examples on this page:
http://dongoodrichpottery.com/potpixd.htm
where most of the pieces are FB on porcelain, with one on buff stoneware,
among a few other glazes.
The recipe used here is:
47.3 Nepheline syenite
27 Gerstley borate
20.3 Silica
5.4 Kaolin
2 Red iron oxide
1.5 Cobalt carbonate
4 Rutile
2 Bentonite
In my experience, I can get a deeper, richer blue by refiring
at cone 5 after firing to cone 6. No idea why this works.
Also of note is that refiring it to cone 04 gives a
celedon-like grey-green,although it lacks the translucency
of true celedons I've seen.
Good luck in your Floating Blue quest. It can be cantankerous, but it has
generated a lot of repeat customers for me since Ms Skeen introduced me to
it a few years ago.
Don Goodrich
goodrichdn@aol.com
William & Susan Schran User on sat 18 feb 06
On 2/17/06 7:57 PM, "Don Goodrich" wrote:
> In my experience, I can get a deeper, richer blue by refiring
> at cone 5 after firing to cone 6. No idea why this works.
When we were firing ^6 at school, I found our "floating blue", that we
labeled "blue hares fur" gave the best results fired fast to ^5 with a
fairly quick cool down. A slower fire, a little higher temperature and
especially a slow cool down would produce a more green color.
I would assume the higher temperature combined with a slow controlled cool
down will allow for more of an interaction between the colorants and the
boron in the glaze.
If your clay is sufficiently vitrified at ^5, you might want to fire a kiln
of all floating blue to ^5 and cool down faster - remove spy hole plugs &
keep vent running.
-- William "Bill" Schran
Fredericksburg, Virginia
wschran@cox.net
wschran@nvcc.edu
Ivor and Olive Lewis on sun 19 feb 06
An interesting thing about phase separation blue is that, were you able =
to observe the layer of glaze from the opposite direction, that is, =
looking towards the incident light rather than at the reflection, the =
hue would have an orange tint.=20
This physical effect can also influence the hue and tonality of white =
porcelain bodies. Seen by reflected light they will have a blue cast but =
when you look and see transmitted light it has a weak dull orange cast.
Best regards,
Ivor Lewis.
Redhill,
South Australia.
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