Kathy McDonald on thu 23 mar 06
Well..finally spring on the prairies and this is
the time that I go out to the garage/summer studio
and start getting set up for summer production.
Clean up time,,,in other words.
In the past I have always taken small portions of
glazes that are left over and/or dried out and
glazes that I didn't really like that well, or have
decided not to use again and dumped them all into
one big bucket and added about 5 kg of my white glaze
some copper and cobalt to the mix. (Kinda like I cook, not
terribly scientific I admit.)
I fire to cone 10 R.
This results in what I call a "shop glaze" that I use
mainly for the outsides of pieces and sometimes for
whole pieces ......if..... it turns
out good that year. The glaze is normally somewhere
between what I would call a satin matte
and a semi gloss opaque blue/green colored glaze.
Each year it's different.
Some year's it's been spectacular.
Glazes that are thrown in usually consist of some copper
reds
that I mix but don't like, a few cone 6 "screw-ups" , some
commercial
cone 6 glazes that are left over after winter and of course
my primary base glaze that comprises most of the shop
glaze...
which is a hi calcium white cone 10 glaze.
I know it can't be replicated this way , nor do I care I
like
the element of surprize. I normally use a liner glaze on
functional ware but am wondering what, if any, safety issues
exist to customers with this practice. I also know other
potters and some large studios that use this practice ,
however
they also use these glazes on the insides of functional cook
and tableware.
I would not do that.
Just looking for feedback from others and their thoughts on
the practice.
Kathy
.
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Ann Brink on thu 23 mar 06
Hi...I'm definitely not one of the glaze experts, but just want to tell you
that's exactly what I do. Adding opaque white to what I call "washbucket"
glazes has given me some interesting aquas and modulated blues. As far as
safety goes, my theory is: no harmful materials in- none out. If it's not a
crazing glaze, I use it inside pieces as well.
Ann Brink in Lompoc CA
Kathy wrote:"> In the past I have always taken small portions of
> glazes that are left over and/or dried out and
> glazes that I didn't really like that well, or have
> decided not to use again and dumped them all into
> one big bucket and added about 5 kg of my white glaze
> some copper and cobalt to the mix. (Kinda like I cook, not
> terribly scientific I admit.)
> I fire to cone 10 R.
>
> This results in what I call a "shop glaze" that I use
> mainly for the outsides of pieces and sometimes for
> whole pieces ......if..... it turns
> out good that year. The glaze is normally somewhere
> between what I would call a satin matte
> and a semi gloss opaque blue/green colored glaze.
> Each year it's different.
> Some year's it's been spectacular.
Donna Kat on fri 24 mar 06
On Thu, 23 Mar 2006 05:08:01 -0600, Kathy McDonald
wrote:
>In the past I have always taken small portions of
>glazes that are left over and/or dried out and
>glazes that I didn't really like that well, or have
>decided not to use again and dumped them all into
>one big bucket and added about 5 kg of my white glaze
>some copper and cobalt to the mix. (Kinda like I cook, not
>terribly scientific I admit.)
>I fire to cone 10 R.
>
>This results in what I call a "shop glaze"
>Just looking for feedback from others and their thoughts on
>the practice.
>
>Kathy
We do this in the studio I'm sometimes at and it is called 'mystery glaze'
which we treat as not food safe because of the high copper content in a
couple of glazes. It is as you say, sometimes gorgeous and sometimes 'blah'
and of course, never replicable.
Crista Nelson on fri 24 mar 06
We do this at the school I attend, at the end of each semester what we do is
take the glaze left over from the bottom of the bucket used for rinsing the
glaze mixer and add it to our X glaze bucket, each time it is done we add an x
to the name it is now called xxx glaze or triple x glaze as we have only
done this 3 times so far, the color always seems to come out a dark bluish green
color with semi matte and glossy areas depending on the thickness, glossier
where thicker.. Crista.....
lee love on fri 24 mar 06
I mix all of my standard wood ash glaze tests together. They always
end up looking like my primary glaze. It makes sense, because my
tests go either side of where I think it will work best.
--
Lee In Mashiko, Japan
http://mashiko.org
http://seisokuro.blogspot.com/
"On the internet, nobody knows you are a dog."
Donald G. Goldsobel on fri 24 mar 06
It is amazing that all shop glazes seem to look similar. Warren McKenzie
reported he swept the glaze dripping sfrom the floor, added cobalt and got a
nice blue. I think if most potters added cobalt to the leftovers, you'd get
green black. If there is rutile in the blend it will prevent the cobalt from
producing the usual blue and dolomite will do the same.
I has its uses. I put it under Coleman's green patina and get great
combonations depending on varying thicknesses.
D
Ivor and Olive Lewis on sat 25 mar 06
Dear Kathy McDonald,
You say=20
...... and dumped them all into one big bucket and added about 5 kg of =
my white glaze some copper and cobalt to the mix. (Kinda like I cook, =
not
terribly scientific I admit.) I fire to cone 10 R...... I normally use a =
liner glaze on
functional ware but am wondering what, if any, safety issues
exist to customers with this practice......
Your mixture has an unknown composition. It would be impossible without =
an analysis to reveal the proportions of the ingredients to say anything =
definitive about its chemistry and hence its durability.
I have been unable to find any evidence that Copper, used as oxides or =
carbonates, enters into a direct chemical relationship with Silicon =
Dioxide. Except for some natural minerals where the copper ion is =
coordinated with Water as a complex Ion Copper oxide of either flavour =
remain in their molecular state in a glaze and are accessible to =
corrosive fluid. It seem fair to suggest that Copper will always leach a =
glaze in which it is an ingredient. This would be true even if there was =
only a small percentage present
Steve Slatin on sat 25 mar 06
OK, temptation drew me in ...
First, REVIEW YOUR RECORDS. Make sure you didn't
dump anything unacceptable into a glaze that got
iteself dumped into the mix. No lead, cadmium,
etc. in your workshop equals no unacceptables in
your shop glaze. Probably that's the case.
Second, TEST THE GLAZE. Lemon (or vinegar) test
for leaching; examine closely under loupe for fit
irregularities, do a thermal shock test, etc.
If you have a good at-home test for alkali attack
or utensil marking, use it. Treat a few test
pots roughly, run them through the dishwasher and
microwave to see how they react, and examine
again under a loupe.
You'd probably do this for a new glaze. No
reason not to do it for a big bucket of unknown.
Third, give it a name you can use with a straight
face in front of a client. I call mine gretas
(for garbo, yes, but that's sufficiently obscure
that people don't ask). My second naming
convention is based on the appearance of the
glaze before firing. One has a great number of
tests that include low %'s of RIO -- they
collectively are a light pink, so I call that one
Pink Greta. The other had a number of tests with
Alberta slip in them as a major ingredient; they
came out black, so I call it Black Greta.
(Black Greta was good enough that I reverse
engineered it and got a 'real' formulated glaze
to get the color and effect. Pink Greta is a
super overglaze when applied over Lili K's
reformulation of Tony Yeh's brown. By itself it
fires light blue. A year's worth of left overs
and stuff cleaned off the glazing table went into
these two glazes, simultaneously reducing my
dependence on purchased materials and my waste
stream, and freeing up a few plastic buckets for
more tests.)
Last, be sensible. As Ivor points out, those
pesky Cu atoms just keep getting away. If you
have, at most, a half concentration of your Cu
containing glaze in the final mix, you've got at
most half concentration of Cu (and likewise
everything else). If it passes the tests, it as
good for daily use as your regular glazes that
pass the same tests.
Best wishes -- Steve S
--- Ivor and Olive Lewis
wrote:
> Dear Kathy McDonald,
>
> Your mixture has an unknown composition. It
> would be impossible without an analysis to
> reveal the proportions of the ingredients to
> say anything definitive about its chemistry and
> hence its durability.
>
> I have been unable to find any evidence that
> Copper, used as oxides or carbonates, enters
> into a direct chemical relationship with
> Silicon Dioxide. Except for some natural
> minerals where the copper ion is coordinated
> with Water as a complex Ion Copper oxide of
> either flavour remain in their molecular state
> in a glaze and are accessible to corrosive
> fluid. It seem fair to suggest that Copper will
> always leach a glaze in which it is an
> ingredient. This would be true even if there
> was only a small percentage present
>
Steve Slatin --
In the mornin’ cry of the rooster
The baby lay alone
And the old cow in the green grass
Shed white tears in the red hot sun
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Ron Roy on sat 25 mar 06
Hi Kathy,
You can always do the lemon test to see if the glaze is grossly unstable.
You should have such glazes lab tested for leaching if you are going to use
them as liner glazes.
In this case you may find those comercial cone 6 glazes may be the weak link.
A good test to see if glazes are durable in an alkaline bath (dish washer)
is to make two test tiles with the glazes on each - leave one in the dish
washer and keep the other out as a control - just compare the two every
month to see if there is any change.
RR
>Well..finally spring on the prairies and this is
>the time that I go out to the garage/summer studio
>and start getting set up for summer production.
>Clean up time,,,in other words.
>
>In the past I have always taken small portions of
>glazes that are left over and/or dried out and
>glazes that I didn't really like that well, or have
>decided not to use again and dumped them all into
>one big bucket and added about 5 kg of my white glaze
>some copper and cobalt to the mix. (Kinda like I cook, not
>terribly scientific I admit.)
>I fire to cone 10 R.
>
>This results in what I call a "shop glaze" that I use
>mainly for the outsides of pieces and sometimes for
>whole pieces ......if..... it turns
>out good that year. The glaze is normally somewhere
>between what I would call a satin matte
>and a semi gloss opaque blue/green colored glaze.
> Each year it's different.
>Some year's it's been spectacular.
>
>Glazes that are thrown in usually consist of some copper
>reds
>that I mix but don't like, a few cone 6 "screw-ups" , some
>commercial
>cone 6 glazes that are left over after winter and of course
>my primary base glaze that comprises most of the shop
>glaze...
> which is a hi calcium white cone 10 glaze.
>
>I know it can't be replicated this way , nor do I care I
>like
>the element of surprize. I normally use a liner glaze on
>functional ware but am wondering what, if any, safety issues
>exist to customers with this practice. I also know other
>potters and some large studios that use this practice ,
>however
>they also use these glazes on the insides of functional cook
>and tableware.
>
>I would not do that.
>
>Just looking for feedback from others and their thoughts on
>the practice.
>
>Kathy
Ron Roy
RR#4
15084 Little Lake Road
Brighton, Ontario
Canada
K0K 1H0
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