Dale McCleskey on mon 26 jan 98
Dale McCleskey
01/26/98 07:15 AM
I just fired a new, to me, clear glaze I got off this list. Cone 6,
oxidation. Glaze called "absolutely clear, recipe:
40 custer spar
30 ghastly borate
20 ball clay (OM4)
10 flint
Results beautiful except my blue (cobalt) slip went black under this clear.
Slip applied to leather-hard piece, bisqued, then dipped in clear. Anybody
with an answer to whats happening? Is the iron in the OM-4 ball clay
joining the cobalt to make black? Am I the guest recipient of a voodoo
curse? What are all those cows chewing on when they're just laying around?
I hate to have to abandon this glaze because, like me, its so cheap and
simple.
Dale McCleskey, Nashville, TN, USA, Confused.
douglas gray on tue 27 jan 98
In message Dale McCleskey writes:
> I just fired a new, to me, clear glaze I got off this list. Cone 6,
> oxidation. Glaze called "absolutely clear, recipe:
> 40 custer spar
> 30 ghastly borate
> 20 ball clay (OM4)
> 10 flint
>
> Results beautiful except my blue (cobalt) slip went black under this clear.
> Slip applied to leather-hard piece, bisqued, then dipped in clear. Anybody
> with an answer to whats happening? Is the iron in the OM-4 ball clay
> joining the cobalt to make black? Am I the guest recipient of a voodoo
> curse? What are all those cows chewing on when they're just laying around?
> I hate to have to abandon this glaze because, like me, its so cheap and
> simple.
Dale
I doubt that there is enough iron in the ball clay to cause your blue slip to go
balck. Ball Clay, by itself, fires out almost white. How much cobalt, or stain
do you have in the slip itself. Maybe you could try to cut the amount in half
and see if the color lightens to blue again. Really strong concentrations of
cobalt, if your are using cobalt, can produce black. Try cobalt carbonate if
you are using coablt oxide. Just a thought.
doug
============================================================================ =)
Douglas E. Gray, Assistant Professor of Art
P.O. Box 100547
Department of Fine Arts and Mass Communication
Francis Marion Univeristy
Florence, South Carolina 29501-0547
dgray@fmarion.edu
803/661-1535
Michelle Harris on wed 28 jan 98
>
> In message Dale McCleskey writes:
>
> > I just fired a new, to me, clear glaze I got off this list. Cone 6,
> > oxidation. Glaze called "absolutely clear, recipe:
> > 40 custer spar
> > 30 ghastly borate
> > 20 ball clay (OM4)
> > 10 flint
> >
> > Results beautiful except my blue (cobalt) slip went black under this clear.
'
> I doubt that there is enough iron in the ball clay to cause your blue slip to
> balck.
I agree that it is not the iron in the slip that causes the poor color
of blue. I think for sure it is the glaze that is mostly to blame,
(although you may also need to finetune the colorants you put into your
slip) I too use a dark blue slip under a clear glaze on most of my work,
and have found 4 glaze considerations:
1. will it craze?
2. will the glaze evoke a good or poor color response.
3. will the glaze let the slip decoration stay fixed, or will it cause
it to flow and move
4. will the glaze go rough (almost pebbly) over the areas with slip
Before Christmas i tested a wide variety of clear glazes and
combinations of them. The results varied widely. Like you, some of the
tests made the slip go dull and dead looking blackish teal blue instead
of a deep sparkly navy. I settled on the following:
Frit 3134 50
Pioneer kaolin 25
silica 25
bentonite 1-2
Ron Roy furthur modified it, which i tested and liked, to this:
Untitled Recipe 2
-----------------
F3134............... 44.00 43.14%
CUSTER SPAR......... 23.00 22.55%
EPK................. 20.00 19.61%
SILICA.............. 13.00 12.75%
=BENTONITE........... 2.00 1.96%
----------
102.00
Unfortunately, it is more expensive than the glaze you mentioned,
because of the amount of frit. However, the other glazes that i liked
the color response either crazed badly, or the slip moved a lot under
the glaze.
As Doug said, it could also be you need to play with the comb and % of
colorants, if you're interested, i can go dig out my recipe. You can
see photos of my pots (and the slip) this month at,
http://www.virtualsk.com/current_issue/computers_and_clay.html
Good luck,
Michelle
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