David Hendley on wed 3 mar 99
At 07:33 AM 3/2/99 EST, you wrote:
>I will say this and maybe I will step on some toes. There seams to be a cult
>developing around limit formulas and calculation as the answer to all
questions.
>I am with Steve on this one. Glazes that are worth applying on handmade
pots are
>outside the guides. So they are not perfectly balanced but they sure look
good.
>We must realize that we don't make utilitarian pots to compete with industry
>(technically perfect) if this is the case you as a studio potter will always
>create an inferior product to the industrial standard.
Ouch! Right on my big toe.
Maybe you and Steve are not talking about functional pottery.
A lot of us make utilitarian pottery, not to compete with industry,
but as an alternative to factory-made ware.
I can tell you, without a doubt, that it is possibe to use durable,
functional glazes, that are within the established limits, that
are beautiful to look at.
We functional potters who develop claybodies and glazes that are
functionally sound get tired of "artists" who know nothing about
glaze formulation, and don't care to know, selling "pseudo-functional"
pottery that leaches, seeps, or doesn't work.
It gives all handmade pottery a bad rap and we are left to explain
that we know what we are doing technically and our pottery
is truly functional.
Computerized glaze calculation is an absolute boon to functional
potters because we can see what's going on in a glaze without
spending 20 minutes doing arithmetic, as we did in in the pre-pc age.
Of course it's not the "answer to all questions", but it's important.
Go ahead and put your unbalanced, crazed, leaching glaze
on your art, but as soon as you put that glaze inside a bowl
you are making an implied statement that it is a functional glaze.
If it is not, I would consider that grossly negligent.
The goal of a functional potter IS to make pottery that is
technically perfect, as well as artistic inspired, and a pleasure to
use. As to the "industry standard", I would put my Ron Roy mug
to the test against anything produced in a factory. It is in no way
technically inferior, with the added bonus that is breathes life.
Best wishes,
David Hendley
Maydelle, Texas
hendley@tyler.net
http://www.farmpots.com
>----------------------------Original message----------------------------
>Hello Clayarters,
>I am compelled to respond to Steve's comments about "breaking the rules".
First
>of all the implication in this statement is that somehow if you are
breaking a
>rule in of itself is art. I would be very surprised if you can make
anything in
>clay worth a look, without you having to follow some rules: be it clay
>preparation, firing schedule, cooling and so on.
>I am not quite sure what it is that you are trying to say. Perhaps you are
>referring exclusively to unity formula limits ? They are guide lines not
limits
>as such. Kind of like learning perspective drawing (definite rules there)
when
>your interest is to free draw. It gives you a frame work to be able to
visualize
>a glaze before mixing (an educated guess at best).
>
>I will say this and maybe I will step on some toes. There seams to be a cult
>developing around limit formulas and calculation as the answer to all
questions.
>I am with Steve on this one. Glazes that are worth applying on handmade
pots are
>outside the guides. So they are not perfectly balanced but they sure look
good.
>We must realize that we don't make utilitarian pots to compete with industry
>(technically perfect) if this is the case you as a studio potter will always
>create an inferior product to the industrial standard. Simply put they
have real
>ceramic engineers on staff, technicians and equipment to monitor and keep
>controls. Where we can excel is in expression, warmth, uniqueness, and so on.
>
>Lastly, the guides were meant for hi-fire only where they make a bit of
sense.
>At medium range, low medium-range, and low-fire the boron is the monkey ranch
>(lead excluded). Sixteen years ago when John Eden was developing his glaze
>calculation program I asked him to make it so one can include B2O3 in the RO
>column, and in some cases it made sense but most of the time it didn't.
The only
>guides that I found useful are Robert Schmitz guides (at least he
acknowledges
>that there is such thing as low-fire and mid-range) in Richard Zakins' book
>Ceramics Mastering the Craft.
>
>Happy Potting,
>
>Paul Rozman
>700 Russell Road, RR# 2
>Ladysmith, BC, V0R 2E0
>Canada
>TL. (250) 245-1055
>
>http://www3.bc.sympatico.ca/mtopottery
>
>mtopottery@bc.sympatico.ca
>
Beth Ward on thu 4 mar 99
<< Go ahead and put your unbalanced, crazed, leaching glaze
on your art, but as soon as you put that glaze inside a bowl
you are making an implied statement that it is a functional glaze.
If it is not, I would consider that grossly negligent. >>
I took the glaze and color development class with Robin Hopper. I learned a
hell of a lot in the class (but please do not ask my opinion of Mr. Hopper.)
Anyway in this class was a woman from Canada who inspite of recent
information about barium glazes leeching into liquids, insisted that she
"loved the barium blues" and until there was conclusive research about the
problems, she would continue to use them.
I found this totally irresponsible.
As makers of functional ware, it is an obligation to calculate carefully and
HARM NO ONE!!
Beth
Muddfolks@aol.com
John Hesselberth on fri 5 mar 99
David Hendley wrote:
>----------------------------Original message----------------------------
>I can tell you, without a doubt, that it is possibe to use durable,
>functional glazes, that are within the established limits, that
>are beautiful to look at.
>Of course it's not the "answer to all questions", but it's important.
>Go ahead and put your unbalanced, crazed, leaching glaze
>on your art, but as soon as you put that glaze inside a bowl
>you are making an implied statement that it is a functional glaze.
>If it is not, I would consider that grossly negligent.
>
Dave,
I agree with most of what you way; however I must take issue with the
implication that if you stay within established limits you will have a
durable, non leaching glaze. There is absolutely no data in the
published literature to confirm that. With the very limited testing I
have done, I have seen glazes within limits that leach and at least one
glaze outside of limits that doesn't leach. I do believe the odds are
higher of having a durable glaze if you stay within limits, but that is
only a gut feeling at this time--I do not have enough data to support
that statement. If anyone does, I would welcome seeing it.
We must remember that the limits were derived, for the most part, by
examining glazes people were using and the criteria of getting "good
glass", i.e. a visual examination of the glaze. So, for example, the
limits for Bristol glazes were established by looking at the unity
formulas of the Brisol-like glaze variants people were using at the
time--nothing more scientific than this!
Currently there is no way to assure getting a durable glaze--inside or
outside of limits--other than to do your own testing on the criteria that
are important to its function. Staying within limits guarantees nothing.
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"
Hank Ray on fri 5 mar 99
In a message dated 3/4/99 3:28:58 PM !!!First Boot!!!, Muddfolks@AOL.COM
writes:
> I took the glaze and color development class with Robin Hopper. I learned a
> hell of a lot in the class (but please do not ask my opinion of Mr.
Hopper.)
So what is your opinion of Mr. Hopper? i would be interested...
Pete in OKC, OK.
Ruth Ballou on fri 5 mar 99
Using durable glazes that do not leach toxic materials for the interiors of
functional pots is definitely the responsible way to go. John Hesselberth
has posted extensive research on his website,
http://www.frogpondpottery.com. Glaze limits were not developed to predict
glaze durability. Glaze limits resulted from research done in the 19th
century and the first part of this century. They were used to show where
one might get a "good glass." As I understand it, even the term "good
glass" is not well defined, other than by general statements such as
surface appearance and being free of surface defects. A visual inspection
of the glaze sufficed.
To depend on glaze limits to predict whether a particular glaze is safe or
not could lead the conscientious potter to make a big mistake. If a glaze
is outside the limits, a potter might erroneously decide that the glaze is
not safe and go to great expense and trouble to replace a glaze that is, in
fact, safe. The Floating Blue or Broken Blue glaze that so many ^6 potters
use is a case in point. It has now been tested by the Alfred lab and been
found to have very low leaching levels. However, it's outside the limits on
several oxides. Conversely, depending that a will not leach if it is
formulated within the limits, could also easily prove to be wrong. The only
way to be sure is to have the glaze tested at a lab.
I don't mean to imply that glaze limits are not useful. They are one tool
to use in understanding why a particular glaze looks and behaves the way it
does. They are useful when you're trying to correct a problem. But there
are many exceptions. For example, no one knows what to do with boron. Up to
a point, it improves glaze durability, then durability suffers. No one
knows what that point is, and it may vary from glaze to glaze. Glaze limits
are guidelines, useful for understanding, but not hard and fast rules. It
helps to also have some understanding of the roles of the individual
oxides, their characteristics, what each brings to the glaze melt. This
information is not reflected in glaze limits.
It seems to me that some terms are being used without adequate definition.
For example, what do we mean by a balanced glaze? We may agree that
durability is important for glazes on the insides of vessels used for food.
How do we define durability? What hardness should a glaze be? It seems if
we're going to use these terms, then we need to have some data to back up
our definitions. Industry has standards and specifications for
freezing/thawing of tiles, which kinds of tiles can be used on floors or
walls, glazes on sanitary ware, etc. Are these standards appropriate for
potters? I'd think we'd find them too limiting. But each of us must take
responsibility for the glazes we use and we need to be sure of the
standards we're applying.
Ruth Ballou
Silver Spring, MD
Michele Hoskin on sat 6 mar 99
I have considered taking the course as well. I visited Mr. Hopper's
pottery a few years ago but he seemed very impressionable: he didn't even
come out to the shop from his studio (attached) when I indicated to his
wife that I was a beginning potter and has read and admired his books and
work. Is he as gruff as they say?
-----Original Message-----
From: Hank Ray [SMTP:Helllll@aol.com]
Sent: Friday, March 05, 1999 1:04 PM
To: CLAYART@LSV.UKY.EDU
Subject: Re: limits and functional pottery
----------------------------Original message----------------------------
In a message dated 3/4/99 3:28:58 PM !!!First Boot!!!, Muddfolks@AOL.COM
writes:
> I took the glaze and color development class with Robin Hopper. I learned
a
> hell of a lot in the class (but please do not ask my opinion of Mr.
Hopper.)
So what is your opinion of Mr. Hopper? i would be interested...
Pete in OKC, OK.
Stephen Grimmer on sun 7 mar 99
Hi,
I spoke with Mr. Hopper a few years back at the Rochester NCECA, and found
him quite approachable. He chatted with me for quite a while about his book,
_Functional Pottery_ , and it was an enjoyable exchange. I didn't think he
was gruff at all.
steve grimmer
marion illinois
----------
>From: Michele Hoskin
>To: CLAYART@LSV.UKY.EDU
>Subject: Re: limits and functional pottery
>Date: Sat, Mar 6, 1999, 8:02 PM
>
>----------------------------Original message----------------------------
>I have considered taking the course as well. I visited Mr. Hopper's
>pottery a few years ago but he seemed very impressionable: he didn't even
>come out to the shop from his studio (attached) when I indicated to his
>wife that I was a beginning potter and has read and admired his books and
>work. Is he as gruff as they say?
>
>-----Original Message-----
>From: Hank Ray [SMTP:Helllll@aol.com]
>Sent: Friday, March 05, 1999 1:04 PM
>To: CLAYART@LSV.UKY.EDU
>Subject: Re: limits and functional pottery
>
>----------------------------Original message----------------------------
>In a message dated 3/4/99 3:28:58 PM !!!First Boot!!!, Muddfolks@AOL.COM
>writes:
>
>> I took the glaze and color development class with Robin Hopper. I learned
>a
>> hell of a lot in the class (but please do not ask my opinion of Mr.
>Hopper.)
>
>So what is your opinion of Mr. Hopper? i would be interested...
>
>Pete in OKC, OK.
>
Ron Roy on thu 11 mar 99
There is some interesting reading on this subject in Ceramics Glaze
Technology by Tayor and Bull (ISBN 0-08-033465-2 and 0-08-033466-0) Chapter
9.2 on the subject of durabiliy. They say glazes with muticomponet glazes
with 60% silica - the standard for sanitary ware.
The following hypothetical glaze (I'll bet it's a clear, well melted glazes
at cone 6) has 60.31% silica - and it's within the limits of the one set of
limits I use. I'm willing to bet my socks (a dubious treasure I know) it's
and acid and alkaline resistant glaze.
RR's hypothetical durable
-----------------
F3134.........................20.00
G 200 SPAR..............14.00
WOLAST...................14.00
STRONT CARB..........5.00
TALC............................8.00
EPK.............................23.00
SILICA........................16.00
----------
Total.........................100.00
FORMULA & ANALYSIS
------------------
*CaO........ .55 11.39%
MnO2....... .00 .02%
*MgO........ .19 2.79%
*K2O........ .05 1.68%
*Na2O....... .12 2.71%
Fe2O3...... .00 .21%
TIO2....... .00 .07%
B2O3....... .19 4.89%
AL2O3...... .32 12.18%
SiO2....... 2.72 60.31%
P2O5....... .00 .03%
*SrO........ .10 3.72%
RATIO 8.42
EXPAN 445.05 (will not craze on most cone 6 bodies and porcelains)
WEIGHT 270.48
Any addition of a zirconium silicate (zircopax, superpax etc. ) will
further increase resistance to acid and alkaline attack.
Ron Roy
93 Pegasus Trail
Scarborough, Ontario
Canada M1G 3N8
Tel: 416-439-2621
Fax: 416-438-7849
Web page: http://digitalfire.com/education/people/ronroy.htm
Barney Adams on fri 12 mar 99
I'm thinking of trying to get a boron blue at cone 6. I've had some
success with some existing glazes but I'd like to get just the boron
blue if I can. From my reading this seems to require a low alumina
high alkaline glaze and probably the high end for B2O3. I've got a few
recipes to work on and test, but it got me to thinking. Is it possible
to find a glaze with no alumina that is durable and safe? Are there
any other material that can be added to the glaze to replace the alumina?
I've read that crystal glazes have been formulated without alumina, and
I can imagine they were runny. If I kept the CaO and MgO high would the
CaO give me enough durablity and the MgO stiffen it enough to make it
usable? The silica would be high and then I'd probably need to push the
KNaO to bring the co-eff of expn up. Or is the alumina component that
critical?
Barney
Ron Roy wrote:
> ----------------------------Original message----------------------------
> There is some interesting reading on this subject in Ceramics Glaze
> Technology by Tayor and Bull (ISBN 0-08-033465-2 and 0-08-033466-0) Chapter
> 9.2 on the subject of durabiliy. They say glazes with muticomponet glazes
> with 60% silica - the standard for sanitary ware.
>
> The following hypothetical glaze (I'll bet it's a clear, well melted glazes
> at cone 6) has 60.31% silica - and it's within the limits of the one set of
> limits I use. I'm willing to bet my socks (a dubious treasure I know) it's
> and acid and alkaline resistant glaze.
>
> RR's hypothetical durable
> -----------------
> F3134.........................20.00
> G 200 SPAR..............14.00
> WOLAST...................14.00
> STRONT CARB..........5.00
> TALC............................8.00
> EPK.............................23.00
> SILICA........................16.00
> ----------
> Total.........................100.00
>
> FORMULA & ANALYSIS
> ------------------
> *CaO........ .55 11.39%
> MnO2....... .00 .02%
> *MgO........ .19 2.79%
> *K2O........ .05 1.68%
> *Na2O....... .12 2.71%
> Fe2O3...... .00 .21%
> TIO2....... .00 .07%
> B2O3....... .19 4.89%
> AL2O3...... .32 12.18%
> SiO2....... 2.72 60.31%
> P2O5....... .00 .03%
> *SrO........ .10 3.72%
>
> RATIO 8.42
> EXPAN 445.05 (will not craze on most cone 6 bodies and porcelains)
> WEIGHT 270.48
>
> Any addition of a zirconium silicate (zircopax, superpax etc. ) will
> further increase resistance to acid and alkaline attack.
>
> Ron Roy
> 93 Pegasus Trail
> Scarborough, Ontario
> Canada M1G 3N8
> Tel: 416-439-2621
> Fax: 416-438-7849
>
> Web page: http://digitalfire.com/education/people/ronroy.htm
| |
|
