Tena Payne on wed 4 aug 99
I have aculpla questions that maybe some of you more
chemically-literate potters can help me with. I'll be asking different
questions about two separate glazes.
I tested this 20x5 glaze at ^6. It has 20% of each listed:
wollastonite, frit 3134, kaolin, flint, and custer feldspar. I added 4%
cobalt and got a great cobalt blue. My question is 'how can I adjust
this glaze to make it more durable?' It's a high-gloss surface that
tends to scratch easily. I need it for dinnerware and it needs to stand
up better under use. If I can't adjust this glaze, does anyone have an
alternate ^6 hard-surfaced clear base that I could test?
Second glaze, next question. This is a Charles Counts' glaze:
Frit 3134 25.4
Neph Sye 34.9
Whiting 5.6
G. Borate 3.7
Flint 25.4
My studio assistant mixed this glaze and misread the percentage of the
colorants. She added:
10% rutile
5% copper
10% red iron oxide
(she picked up a previous test I had done)
Now the resulting glaze isn't that bad... just not what I wanted. It's
a metalic cammo green and where it's thick it's almost gun-metal grey.
Can this glaze batch be saved? (or redeemed?) (I have tested it under
the above cobalt glaze with interesting effects.) So I can just use it
that way if nothing else.
Is there anything I can do/add to make this bucket of stuff look better
than it does?
Thanx for your help and forgive my ignorance. (ignorance can be cured,
stupidity can't.) I'm working on both. ;>
Tena
Birmingham, AL
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Sue Beach on sun 9 feb 03
Hello group.
I made up three 3,000 gram batches of one of the base glazes in Ron &
John's book. One batch I left white, one was colored with copper, one with
cobalt carb. I seem to have added too much water, maybe? The pots seemed
thoroughly covered with glaze when they went into the kiln. When the pots
came out of the glaze firing, they had patches of raw clay, patches of
thinly glazed spots & patches that were fully covered, but much more matte
than my test tiles had been. The glaze is SO different than the test
batch! The test batches were wonderful, so I took the leap & mixed up the
large batches.
The next time I fired, I tried taking water off the top before mixing up
the glaze. The consistency of the glaze was better - milkish. Pots still
didn't turn out right. Better coverage, but not like it should have been.
And not much color.
So, my question is, do I take off more water? Am I removing soluable
materials along with the excess water? Could I mix up more dry glaze & add
to the bucket to thicken it? That way I could put the removed water back
(I saved it).
This was a disappointing firing because (of course) I had a special order
in the kiln that did not turn out.
IF I can get the glaze fixed, I'll try re-glazing the order.
I sure would hate to have to dump 9,000 grams of glaze, but also hate
ruining good pots.
Suggestions appreciated.
Sue Beach
in the country outside Muncie, Indiana
feeling very discouraged & not much like a potter today.....
Catherine White on sun 9 feb 03
Hi, Sue and everyone else to whom this has happened.
I worked and worked testing a stony turquoise glaze of my own design. Got
it just as I wanted on a large "L" shaped test tile. Dancing about patting
myself on the back.......
Then the pottery piece came out of the same electric kiln fired to the same
^8 temp and checked with pyrometer and cones. The upper surface was an ugly
broken yellowish instead of stony blue-green. The glaze was thin looking.
What a downer. I have pretty well figured out what went wrong, but it does
diminish one's enthusiasm temporarily.
I look forward to the pros' comments on all this since my problems mirror
yours.
Best wishes,
Catherine in Yuma, AZ
My inability to emulate occasionally results in originality.
http://www.clayart.fsnet.co.uk/pp_catherine_white.html
=============================================
----- snip -----
The pots seemed
> thoroughly covered with glaze when they went into the kiln. When the pots
> came out of the glaze firing, they had patches of raw clay, patches of
> thinly glazed spots & patches that were fully covered, but much more matte
> than my test tiles had been. The glaze is SO different than the test
> batch! The test batches were wonderful, so I took the leap & mixed up the
> large batches.
> Sue Beach
> feeling very discouraged & not much like a potter today.....
Pat Southwood on sun 9 feb 03
Sue,
It sounds too thin,
What does your hand look like when you have dipped it in the stirred glaze?
Can you clearly see the wrinkles of your knuckles and your fingers are
virtually bare of glaze, just sort of wet and a bit greyish (way too thin)
or are your knuckles just appearing through the murk?(too thick)
Take out half a pint of water at a time and test the resulting glazes on
tiles or lost and lonely pots.
Mark the tiles clearly, make notes on paper as well as on the tiles.
Patience is a virtue!
Always test a big batch before a special order with a new glaze, yes, I
know, the benefits of hindsight are wonderfull , are they not!!
Been there, done that, thrown those pots away.
Good Luck
Pat.
Stephani Stephenson on mon 10 feb 03
It sounds like the problem -glaze was perhaps too thin....especially if
you are pulling water off.
In some cases , you , now the pottery sleuth , can figure out what
happened not by just examining the glaze
but by examining what kind of differences there were in the clay,
especially the clay surface
i.e. How did the clay on the large pot differ from the test tile clay?
Was the large pot thrown? was the clay pot surface more compressed than
the test tile surface? was it ribbed smooth or, conversely, scraped or
sanded?
was the grog more submerged from the surface or was it more exposed?
Was the surface more sealed? if the pot and the test tile were bisqued
were they bisqued at the same temp? Can you tell anything about the
glaze behavior by looking at the size and shape of the pot? was the pot
curved and the test tiel flat?
I have noticed that certain glazes are sensitive to changes in the
surface of the clay, and sometimes the surface of a pot is more 'worked'
than the surface of a test tile, so it is good to try and mimic the
conditions you will find on the pot, on the test tile. For some of my
glazes, and certain claybodies, if the clay has been either excessively
ribbed with a rubber rib , sealing the surface, or if it has been
sponged, exposing the grog, glaze behavior on the larger, or vertical
pieces, can be affected.
also how was glaze applied to pot v test tile. both dipped or poured? or
was one dipped and one painted?
Stephani Stephenson
steph@alchemiestudio.com
Lily Krakowski on mon 10 feb 03
Forgive my sounding like a street-corner preacher, but Any Glaze Can Be
Saved!!!!
Did you say "milkish" ? "Milk", as in "cow" ? I suspect that is your
problem.
Every glaze has its ideal consistency and every potter has her preference.
Still--The consistency varies with method of application. Sprayed on
glazes--about which I know little--have to be thinner. But for pouring or
dipping the consistency goes from heavy cream to cream soup....for brushing
I go up to commercial Ranch dressing or even yoghurt.
As a rule of thumb, an average glaze goes on a pot to a thickness of a
nickel to two nickels (one on top of each other). Glazes with a lot of
clay, thicker as a rule, those without thinner.
That is why some people measure the water they put in, and some use a
hydrometer.
As a general shot in the dark backup: could you have bisqued the pots too
high? Are there burnished surfaces that fail to absorb water properl˙?
Sue, I do not add this for you, but for newbie readers...
Sue Beach writes:
.....I seem to have added too much water, maybe? ......
> The consistency of the glaze was better - milkish. ..... >
> > ______________________________________________________________________________
Lili Krakowski
P.O. Box #1
Constableville, N.Y.
(315) 942-5916/ 397-2389
Be of good courage....
Paul Lewing on mon 10 feb 03
on 2/9/03 12:50 PM, Sue Beach at sbeach@IQUEST.NET wrote:
> The next time I fired, I tried taking water off the top before mixing up
> the glaze. The consistency of the glaze was better - milkish. Pots still
> didn't turn out right. Better coverage, but not like it should have been.
> And not much color.
>
> So, my question is, do I take off more water?
Yes.
Am I removing soluble materials along with the excess water?
If you were mixing up some other glaze recipe that you did not share the
recipe for, I'd say maybe you were. But I know that Ron and John made a
real effort to devise recipes that used only non-soluble materials. So in
this case, I'd say no.
Could I mix up more dry glaze & add
> to the bucket to thicken it? That way I could put the removed water back
> (I saved it).
You could. But if you made no measuring mistakes when mixing the first
batch, that's not necessary. And there's no need to save the water. If
there had been anything soluble in the original batch, you're probably
better off without it.
>
> This was a disappointing firing because (of course) I had a special order
> in the kiln that did not turn out.
Another perfect example of Lewing's Law of Ceramics. That is "The more you
care about it, the less likely it is to work".
Paul Lewing, Seattle
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