John Hesselberth on tue 30 nov 99
I am finally getting a slow trickle of data from Alfred Analytical (from
those who have told Alfred they could send the results to me). I have
also had regular phone conversations with Roland Hale and Bob LaPlant at
Alfred Analytical (they have been really busy and sending data to me is,
rightly, lower on their priority list than many other things they do).
What I am learning, though, is that there may be a problem keeping more
people from having their glazes tested when they really would like to.
Or, alternatively, some people are not spending their money effectively
by testing for things that aren't there in the first place.
The problem I am sensing is that some of us are so unfamiliar with glaze
chemistry that we don't know what to test for. Therefore we either test
for things that probably aren't in the glaze in the first place or don't
test at all. We may be intimidated by all the techno-speak that is
contained in many of our Clayart messages. Whatever the reason, I am
writing this note to encourage people who are in this situation to ask
for help. I certainly will try to answer any requests for help of this
type that I see. I am certain several other of the glaze-knowledgeable
people on Clayart would also. If you'd rather not ask on-list, then
write me off list.
At the same time, I am trying to help the people at Alfred Analytical to
learn "glaze-speak". We all tend to assume that because they are located
in the same town as a well-known ceramics school that they would have
glaze chemistry in their veins. Not so. As an aside, Alfred Analytical
is not a part of Alfred University. They work closely together in some
areas; however Alfred Analytical is privately owned. They are excellent
analyical chemists who do high quality work but terms like gerstley
borate, nepheline syenite, cone 6, etc. leave them saying, huh??
I guess my whole point of this message is to say: If you want to have
your glazes tested, but need help in any way, please ask--on or off list.
And when you do test, please don't forget to tell Alfred Analytical it's
OK to send the results to me. Or better yet, send them to me yourself--I
will get them faster that way.
John Hesselberth
Frog Pond Pottery
P.O. Box 88
Pocopson, PA 19366 USA
EMail: john@frogpondpottery.com web site: http://www.frogpondpottery.com
"It is time for potters to claim their proper field. Pottery in its pure
form relies neither on sculptural additions nor on pictorial decorations.
but on the counterpoint of form, design, colour, texture and the quality
of the material, all directed to a function." Michael Cardew in "Pioneer
Pottery"
Chris Schafale on wed 1 dec 99
John,
Perhaps it would be useful for you to review the guidelines
for getting a glaze tested. That is, what materials might
potentially be problematic and should be tested for, and what
materials can be considered safe. It occurs to me that one reason
you may not be getting many glazes tested, is that many glazes simply
don't contain anything very dangerous. For instance, I am committed
to getting my glazes tested when necessary, but so far I'm using
glazes that don't really contain toxic materials. I'm not going to
send a glaze off to Alfred to get them to test for iron release,
because I'm just not worried about iron from a glaze being toxic even
if it did leach. I do use cobalt, but my understanding has been
(please correct me if I've got this wrong) that cobalt is very stable
and doesn't tend to leach.
Off the top of my head, I would suggest that glazes
containing barium, lithium, lead, copper, cadmium, vanadium,
manganese, nickel, chrome, and possibly cobalt should be tested for
release of these elements. What else would you add, or take away?
Chris
> ----------------------------Original message----------------------------
> I am finally getting a slow trickle of data from Alfred Analytical (from
> those who have told Alfred they could send the results to me). I have
> also had regular phone conversations with Roland Hale and Bob LaPlant at
> Alfred Analytical (they have been really busy and sending data to me is,
> rightly, lower on their priority list than many other things they do).
> What I am learning, though, is that there may be a problem keeping more
> people from having their glazes tested when they really would like to.
> Or, alternatively, some people are not spending their money effectively
> by testing for things that aren't there in the first place.
>
> The problem I am sensing is that some of us are so unfamiliar with glaze
> chemistry that we don't know what to test for. Therefore we either test
> for things that probably aren't in the glaze in the first place or don't
> test at all. We may be intimidated by all the techno-speak that is
> contained in many of our Clayart messages. Whatever the reason, I am
> writing this note to encourage people who are in this situation to ask
> for help. I certainly will try to answer any requests for help of this
> type that I see. I am certain several other of the glaze-knowledgeable
> people on Clayart would also. If you'd rather not ask on-list, then
> write me off list.
>
> At the same time, I am trying to help the people at Alfred Analytical to
> learn "glaze-speak". We all tend to assume that because they are located
> in the same town as a well-known ceramics school that they would have
> glaze chemistry in their veins. Not so. As an aside, Alfred Analytical
> is not a part of Alfred University. They work closely together in some
> areas; however Alfred Analytical is privately owned. They are excellent
> analyical chemists who do high quality work but terms like gerstley
> borate, nepheline syenite, cone 6, etc. leave them saying, huh??
>
> I guess my whole point of this message is to say: If you want to have
> your glazes tested, but need help in any way, please ask--on or off list.
>
> And when you do test, please don't forget to tell Alfred Analytical it's
> OK to send the results to me. Or better yet, send them to me yourself--I
> will get them faster that way.
>
> John Hesselberth
> Frog Pond Pottery
> P.O. Box 88
> Pocopson, PA 19366 USA
> EMail: john@frogpondpottery.com web site: http://www.frogpondpottery.com
>
> "It is time for potters to claim their proper field. Pottery in its pure
> form relies neither on sculptural additions nor on pictorial decorations.
> but on the counterpoint of form, design, colour, texture and the quality
> of the material, all directed to a function." Michael Cardew in "Pioneer
> Pottery"
>
>
Light One Candle Pottery
Fuquay-Varina, NC
candle@intrex.net
John Hesselberth on thu 2 dec 99
Chris Schafale wrote:
>Perhaps it would be useful for you to review the guidelines
>for getting a glaze tested. That is, what materials might
>potentially be problematic and should be tested for, and what
>materials can be considered safe. It occurs to me that one reason
>you may not be getting many glazes tested, is that many glazes simply
>don't contain anything very dangerous. For instance, I am committed
>to getting my glazes tested when necessary, but so far I'm using
>glazes that don't really contain toxic materials. I'm not going to
>send a glaze off to Alfred to get them to test for iron release,
>because I'm just not worried about iron from a glaze being toxic even
>if it did leach. I do use cobalt, but my understanding has been
>(please correct me if I've got this wrong) that cobalt is very stable
>and doesn't tend to leach.
>
>Off the top of my head, I would suggest that glazes
>containing barium, lithium, lead, copper, cadmium, vanadium,
>manganese, nickel, chrome, and possibly cobalt should be tested for
>release of these elements. What else would you add, or take away?
Good suggestion Chris. Of course any list of this type will generate
controversy. I'm in agreement with the list above that you suggest;
although I would add boron because there is a "health advisory" level for
water of 0.6 mg/l. I still test for cobalt; the data I have seen is
consistent with your statement above, but I haven't seen enough to want
to stop testing for it. The other problem with cobalt (and several of
the others in your list) is that there isn't even a water standard to use
as a guide.
Of the materials I use (I don't use lead, cadmium or barium), I
personally worry most about copper. I like to use it. There is a water
standard for it of 1.3 mg/l and we also know it makes food taste bitter
at about 10 mg/l. I have now seen glazes containing 4-5% copper
carbonate that leach anywhere from next-to-nothing (0.07 mg/l) to a whole
lot (160 mg/l). Quite a range!
John Hesselberth
Frog Pond Pottery
P.O. Box 88
Pocopson, PA 19366 USA
EMail: john@frogpondpottery.com web site: http://www.frogpondpottery.com
"It is time for potters to claim their proper field. Pottery in its pure
form relies neither on sculptural additions nor on pictorial decorations.
but on the counterpoint of form, design, colour, texture and the quality
of the material, all directed to a function." Michael Cardew in "Pioneer
Pottery"
Gail Dapogny on thu 9 dec 99
So John....
Coming to this glaze testing thread late (yeah, I know... duhhh), but
sincere in my interest: if I want to have a glaze tested for barium
leaching, do I:
1.specify the chemical I want it tested for or leave it up to them?
2.include the glaze formula?
3.limit the size piece; I.e. how small is viable? E.g.test tile?
4.specify that they also send results to you?
5.include a check for _____?
6.send a SASE for the results?
7.Send return-mailing costs for the piece to be returned?
And finally...
8.How do I interpret the data that they send me, and how do I relay it
to someone else in understandable and practical terms?
---Thanks for your patience (in advance). ---Gail
Gail Dapogny
1154 Olden Road
Ann Arbor, MI 48103-3005
(734) 665-9816
gdapogny@umich.edu
John Hesselberth on fri 10 dec 99
Hi Gail,
I'm glad you are considering having some glazes tested. See my comments
below:
Gail Dapogny wrote:
>----------------------------Original message----------------------------
>So John....
>Coming to this glaze testing thread late (yeah, I know... duhhh), but
>sincere in my interest: if I want to have a glaze tested for barium
>leaching, do I:
> 1.specify the chemical I want it tested for or leave it up to them?
I'd specify what you want if you know. I always do. They can recommend
if they have the glaze formula, but they are not glaze chemisty experts.
You can also ask advice from most any of the glaze-oriented people on
Clayart. There were a couple messages a few days ago on what you might
consider testing for if those things are in your glaze.
> 2.include the glaze formula?
Please do; although it is not a requirement. Also tell them it's OK to
share the result with me if you are willng. I have already posted the
results from about 15 glazes on my web site and hope to have hundreds a
year from now.
> 3.limit the size piece; I.e. how small is viable? E.g.test tile?
Well, it has to hold liquid. They extract with a 24 hours soak in room
temperature acetic acid. I throw a cup from 350 grams of clay. Others
just send a mug or a cup from their normal production. If you are going
to test several glazes you will get more comparable results if the cups
are about the same size.
> 4.specify that they also send results to you?
Please, in addition to yourself of course.
> 5.include a check for _____?
$10 for each cup for the extraction Plus $10 for each metal to be
analyzed. Example: a sample to be analyzed for barium and copper = $30
> 6.send a SASE for the results?
No, they spring for the postage for that. It normally takes 2-3 weeks,
but they ocassionally get backlogged more or have an equipment breakdown.
> 7.Send return-mailing costs for the piece to be returned?
If you want them returned, they need $15 per order (not per piece) for S/H
>And finally...
> 8.How do I interpret the data that they send me, and how do I
>relay it
> to someone else in understandable and practical terms?
Ahhh, you would get around to that. Of course for lead and cadmium there
are standards that must be met in most countries including the U.S. For
others it is much more judgmental ranging from those who think we should
meet drinking water standards (clearly a safe side, defensible position)
to those who think we are crazy to even worry about the problem except
for lead and cadmium to those (like myself) who are somewhere in between.
My own view is this: I want to learn how to make my glazes as stable as
possible while still being attractive. In addition I have decided to set
an upper limit on leaching for glazes I use on food surfaces of 7-10
times the drinking water standard where one exists. I have chosen this
number ratioing off the lead requirements where the allowable leaching
level is 7-200 times the drinking water standard depending on the type of
vessel. I still think this is on the very safe end of the spectrum while
giving me enough artistic freedom to make and use attractive glazes. It
also challenges me to check my glazes because not all that I develop or
test from other's recipes meet these goals.
By the way, experiments are underway between me and Alfred Analytical to
see how much actually gets into various foods under realistic in-use
conditions. Things like coffee, milk, tomato sauce in a casserole,
orange juice. Results will be available when they get their backlog
worked down.
As to communicating the results to others you are welcome to borrow the
format I use on my site. It is a bit detailed, but it is comprehensive.
And, of course, if you send the results to me I will post them in that
format and you can give people that URL reference (By the way, I get
results much more quickly if you send them to me yourself. If you all
have had glazes tested and don't see them on my site, but would like to,
please send them to me yourself.)
For a more detailed perspective on this, as well as the water and
lead/cadmium standards, check out the words I have written on my web site
and I'll be happy to expand off line if needed. Go to:
http://www.frogpondpottery.com/glazestability/stableglazes.html
Also, if you forget any of the instructions for testing or the address or
whatever, you can find them at:
http://www.frogpondpottery.com/glazetest.html
>
>---Thanks for your patience (in advance). ---Gail
No trouble at all. I enjoy getting the opportunity to give this a little
publicity now and then. John
>
>Gail Dapogny
>1154 Olden Road
>Ann Arbor, MI 48103-3005
>(734) 665-9816
>gdapogny@umich.edu
John Hesselberth
Frog Pond Pottery
P.O. Box 88
Pocopson, PA 19366 USA
EMail: john@frogpondpottery.com web site: http://www.frogpondpottery.com
"It is time for potters to claim their proper field. Pottery in its pure
form relies neither on sculptural additions nor on pictorial decorations.
but on the counterpoint of form, design, colour, texture and the quality
of the material, all directed to a function." Michael Cardew in "Pioneer
Pottery"
John & Anne Worner on fri 5 may 00
Hi John,
I have another glaze I want to have tested. I wondered if it isa
necessary
to have the iron in it tested or if it will suffice with leachate
testing
for the cobalt (formula below).
I got the original recipe from a friend, but it was totally unbalanced,
and crazed on my clay. I have played with it until it is
unrecongnizable
from the original. Is it "kosher" to rename the recipe to AW.....??
I really feel that when people change a recipe they should get credit
for it - this goes for everyone and I guess it could be a subject for
discussion.
An interesting aspect of this glaze is that the addition of cobalt
changed the "feel" of the glaze. I have been using it without cobalt
for some time, but wanted to see if I could get a ^10 black that didn't
shift. I did, and it is quite black, satin. Without the cobalt it is
deep black/brown on porcelain. On stonewares it breaks to a bronze.
In reduction it is bronze breaking to brown - looks cool in both
atmospheres! One of my favorites.
Here's the formula. Let me know.
Anne
Black/Bronze and Black
=======================================
CUSTER FELDSPAR..... 35.65 35.65%
WHITING............. 6.09 6.09%
DOLOMITE............ 10.43 10.43%
FLINT............... 28.70 28.70%
EPK KAOLIN.......... 19.13 19.13%
========
100.00
CaO 1.05 8.73%
MgO 0.43 2.60%
K2O 0.30 4.20%
Na2O 0.13 1.18%
TiO2 0.01 0.08%
Al2O3 1.00* 15.12%
P2O5 0.00 0.05%
SiO2 7.61 67.81%
Fe2O3 0.01 0.22%
Cost/kg 0.57
Si:Al 7.61
SiB:Al 7.61
Expan 6.57
Colorant: 10% RIO
4/00
1. Making a new test batch with
1.5% Cobalt Carbonate.
this is very black with the added cobalt, but the glaze does not feel as
smooth as the original with only RIO
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