Eleanor Arkowitz on wed 3 jan 07
i was given this glaze by another clayarter. i love it and use it on the outside of planters and vases. but when i glazed a test dish and placed a lemon slice on it-wow, did it leach color. is there anything i can do to make it more stable and still keep the wonderful color. also if i can't correct the leaching would it be okay to use it on the outside of pitchers, mugs and bowls and then a white liner inside. does anyone see anything wrong with that idea.
here is the glaze and i am sorry i can't remember who gave it to me.
turquoise glaze ^6 oxid
Nephy. syen. 345
Strontium carb 130
Gerstley borate 12
bentonite 14
Copper carb 19
this shows a great surface on ^6 porcelain. i made 20 planters for a wedding display. would love to b e able to put it to more uses.
thganks for all your help
John Hesselberth on wed 3 jan 07
On Jan 3, 2007, at 10:13 AM, Eleanor Arkowitz wrote:
> i was given this glaze by another clayarter. i love it and use it
> on the outside of planters and vases. but when i glazed a test
> dish and placed a lemon slice on it-wow, did it leach color. is
> there anything i can do to make it more stable and still keep the
> wonderful color. also if i can't correct the leaching would it be
> okay to use it on the outside of pitchers, mugs and bowls and then
> a white liner inside. does anyone see anything wrong with that idea.
> here is the glaze and i am sorry i can't remember who gave it to me.
>
> turquoise glaze ^6 oxid
> Nephy. syen. 345
> Strontium carb 130
> Gerstley borate 12
> bentonite 14
> Copper carb 19
>
> this shows a great surface on ^6 porcelain. i made 20 planters for
> a wedding display. would love to b e able to put it to more uses.
Hi Eleanor,
This glaze is way low on silica to be durable. It is also very likely
not fully melted--the boron is very low for a cone 6 glaze. Either
the low silica or the lack of melting can give you poor resistance to
lemon juice. It would be very difficult to get into a well melted
durable range without losing the turquoise color. If I were going to
attempt it I would take the GB up to at least 100 and add 100-150
parts of silica. Then do a line blend with the original and test each
of the line blends with your lemon slice. You will probably get a
glossier glaze, and I think the chance of retaining the turquoise
color AND passing your lemon test is small. But you will probably
learn a bit about glaze formulation by trying it.
Good luck,
John
Ivor and Olive Lewis on thu 4 jan 07
Dear Eleanor Arkowitz,
I have no proof for this opinion but I think it would be impossible to =
ever find a glaze which used Copper oxide or carbonate that was fired in =
a non reducing situation that did not leach. This is not, in my opinion, =
a functon of the glaze being unstable but due to the fact that Copper =
compounds do not dissolve in a silicate melt or enter into any chemical =
reactions with ingredients of a glaze. Copper will leach, come what may, =
from any glaze.
I think I will set up some tests. It should be possible to make up some =
form of undergalze slip to apply to green ware so that the bisque pot =
can be coated with a clear transparent gloss glaze. This may help to get =
copper green blues under a well sealed surface.
Best regards,
Ivor Lewis.
Redhill,
South Australia.
Ron Roy on fri 5 jan 07
Hi Ivor, Hi Eleanor,
The method we used to determine durability was to add 5% copper carb and 6%
rutile to a glaze and apply the standard leaching test - so it is possible
to make stable glazes that will hold copper to a reasonable level.
RR
>Dear Eleanor Arkowitz,
>
>I have no proof for this opinion but I think it would be impossible to
>ever find a glaze which used Copper oxide or carbonate that was fired in a
>non reducing situation that did not leach. This is not, in my opinion, a
>functon of the glaze being unstable but due to the fact that Copper
>compounds do not dissolve in a silicate melt or enter into any chemical
>reactions with ingredients of a glaze. Copper will leach, come what may,
>from any glaze.
>
>I think I will set up some tests. It should be possible to make up some
>form of undergalze slip to apply to green ware so that the bisque pot can
>be coated with a clear transparent gloss glaze. This may help to get
>copper green blues under a well sealed surface.
>
>Best regards,
>
>Ivor Lewis.
Ron Roy
RR#4
15084 Little Lake Road
Brighton, Ontario
Canada
K0K 1H0
Alisa Liskin Clausen on fri 5 jan 07
On >turquoise glaze ^6 oxid
>Nephy. syen. 345
>Strontium carb 130
>Gerstley borate 12
>bentonite 14
>Copper carb 19
>
Dear Eleanor,
The Turqouise Mat I use is very mat and I do not use it on the inside of
food containors. However, it has far less Cu Carb. then the above and
some Silica, and no G.B. It is quite reliable for a usually persnickety
color. One must use it on the thick side to get a bright turquoise, what
I would call a Persian Blue.
60 Neph. Sye
21 Strontium Car.
9 Silica
4 Ball Clay
2 Lithium Carb.
ADD
4 Cu. Carb.
2 Bentonite
It does not meet your requirements for food friendly, however, it may save
you in Copper carb. and get a good result.
Best regards, Alisa in Denmark
Edouard Bastarache Inc. on fri 5 jan 07
Hello John,
what about adding zirconium silicate intead of
rutile?
Later,
Edouard Bastarache
Le Français Volant
The Flying Frenchman
Sorel-Tracy
Quebec
www.sorel-tracy.qc.ca/~edouardb/Welcome.html
http://perso.wanadoo.fr/smart2000/index.htm
http://www.pshcanada.com/Toxicology.htm
www.thepottersshop.blogspot.com
http://www.ceramique.com/cerambooks/rayons/technologie.php
http://www.flickr.com/photos/30058682@N00/
John Hesselberth on fri 5 jan 07
On Jan 4, 2007, at 2:18 AM, Ivor and Olive Lewis wrote:
> I have no proof for this opinion but I think it would be impossible
> to ever find a glaze which used Copper oxide or carbonate that was
> fired in a non reducing situation that did not leach. This is not,
> in my opinion, a functon of the glaze being unstable but due to the
> fact that Copper compounds do not dissolve in a silicate melt or
> enter into any chemical reactions with ingredients of a glaze.
> Copper will leach, come what may, from any glaze.
Hi Ivor,
Some copper may leach but you can cut down dramatically on the
leaching by adding the copper to a stable base glaze vs an unstable
one. I have a LOT of data showing that. Of course some of every
colorant you put in a glaze will leach if you use a sensitive enough
analytical test. Copper just happens to be the worst I have found.
If you want an additional fact to puzzle over, adding rutile and
copper carbonate to a stable glaze results in less leaching than
adding copper carbonate alone.
Regards,
John
asim mahmood on sat 6 jan 07
>From: John Hesselberth
>Reply-To: Clayart
>To: CLAYART@LSV.CERAMICS.ORG
>Subject: Re: beautiful turq. glaze
>Date: Sat, 6 Jan 2007 14:47:22 -0500
>
>On Jan 5, 2007, at 11:12 PM, Edouard Bastarache Inc. wrote:
>
>>what about adding zirconium silicate intead of
>>rutile?
>
>Hello Edouard,
>
>I don't have any data on that.
>
>John
>
>______________________________________________________________________________
>Send postings to clayart@lsv.ceramics.org
>
>You may look at the archives for the list or change your subscription
>settings from http://www.ceramics.org/clayart/
>
>Moderator of the list is Mel Jacobson who may be reached at
>melpots@pclink.com.
_________________________________________________________________
Dave vs. Carl: The Insignificant Championship Series. Who will win?
http://clk.atdmt.com/MSN/go/msnnkwsp0070000001msn/direct/01/?href=http://davevscarl.spaces.live.com/?icid=T001MSN38C07001
sacredclay on sat 6 jan 07
--- In clayart@yahoogroups.com, John Hesselberth
wrote:
>
John, I am trying to wrap my brain around this concept of Copper
leaching. It has been quite a few years between the time I graduated
from Alfred University and the time that I actually got back into
glaze. There's a wealth of informations out there and I wasn't really
aware of the dangers of Copper leaching until I've visited your
website. If I gather it correctly, any more than 5% copper is consider
unsafe. So rutile will make it less of a leacher, so to speak. How much
percentages to add to how much of copper? I already have all the
websites of lists of materials. I can't get it through my thick skul
what all those numbers mean, so please have patient with my question.
Warmest regards, kathryn in NC
Ivor and Olive Lewis on sat 6 jan 07
Dear Ron Roy ,
In other words, Copper is still going to be taken from a glaze which =
contains it by an acidic liquid. It can never be a permanently fixed =
entity. It is not dissolving in the glaze like Cobalt compounds do or =
entering into chemical reactions like Zinc oxide or Iron will with =
available Silica. It is always in the form of Colloidal metal or one of =
the oxides.
<and 6%
rutile to a glaze and apply the standard leaching test - so it is =
possible to make stable glazes that will hold copper to a reasonable =
level.>>
Best regards,
Ivor Lewis.
Redhill,
South Australia.
John Hesselberth on sat 6 jan 07
On Jan 6, 2007, at 11:51 AM, sacredclay wrote:
> If I gather it correctly, any more than 5% copper is consider
> unsafe. So rutile will make it less of a leacher, so to speak. How
> much
> percentages to add to how much of copper?
Hi Kathryn,
I don't believe I have ever used the word 'unsafe', because I don't
know what the word means. I have said that I have never found a glaze
that will hold more that 5% copper carbonate without leaching a LOT
of copper into acidic material (orange juice or tomato sauce for
example--oh, and coffee too). And that is with the addition of
rutile--I use 6% in most glazes). If you use a good stable base glaze
and keep your copper carbonate below 5% the leaching is generally
fairly low. If you use more than 5% and/or the glaze is a lousy one--
well I can show you glazes where you can draw the color right out of
them by putting a slice of lemon on them for a couple hours. See the
illustrations in MC6Gs for more info.
No, you didn't learn about that at Alfred; although you may have
learned that copper in lead based glazes was a no-no. It has been
known for many decades that copper increased the leaching of lead.
However, no one worried about the leaching of copper when lead was so
much more on their minds. Ron's and my data have shown that copper is
difficult to keep in all but the very most stable glazes and, even
then, 5% is about the maximum they will hold.
By the way, regardless of any potential safety issues, copper will
make food taste bitter as a level as low as 5 ppm. That's not very
much. I certainly don't want my customers to have bitter orange juice
in the morning.
Regards,
John
John Hesselberth on sat 6 jan 07
On Jan 5, 2007, at 11:12 PM, Edouard Bastarache Inc. wrote:
> what about adding zirconium silicate intead of
> rutile?
Hello Edouard,
I don't have any data on that.
John
Ron Roy on sat 6 jan 07
Ivor,
The point is - you can reduce the level of copper leaching to a minimal
level by formulating a durable glaze. It is the durability of the glaze
that is important - not the state of the copper in it.
RR
>Dear Ron Roy ,
>
>In other words, Copper is still going to be taken from a glaze which
>contains it by an acidic liquid. It can never be a permanently fixed
>entity. It is not dissolving in the glaze like Cobalt compounds do or
>entering into chemical reactions like Zinc oxide or Iron will with
>available Silica. It is always in the form of Colloidal metal or one of
>the oxides.
>
><>rutile to a glaze and apply the standard leaching test - so it is possible
>to make stable glazes that will hold copper to a reasonable level.>>
>
>Best regards,
>
>Ivor Lewis.
Ron Roy
RR#4
15084 Little Lake Road
Brighton, Ontario
Canada
K0K 1H0
sacredclay on sat 6 jan 07
Bass, Will zirconium silicate still create the interesting surface
movements that rutile do? I gather it won't have the nice earthy tints
to it.Kathryn in NC>
> what about adding zirconium silicate intead of
> rutile?
>
>
> Later,
>
>
>
> Edouard Bastarache
> Le Fran=E7ais Volant
> The Flying Frenchman
>
sacredclay on sun 7 jan 07
John, WWhen i ever meet you, I am going to hug the HAIL out of you.
It makes alsot of sense now.So copper even in a stable glaze will
affect taste? Sorry if I misquoted you.In all fairness, I don't
quite remember anything about copper in lead based glazes because I
was profoundly deaf at that time and relied on interpreters, who were
a little unstable themselves. Alfred was in the middle of nowhere and
my impressions were that you had to be a hardy soul to live there. No
offense to those who do live there.Barium carbonates where the big
thing and I remember using white lead and red lead too. Finally
elimenate them from all raku glazes. Thanks again for the
clarifications! With warm regards, kathryn in NC and lead-free of a
leacher, so to speak. How
> > much
> > percentages to add to how much of copper?
>
> Hi Kathryn,
>
> I don't believe I have ever used the word 'unsafe', because I don't
>>
> No, you didn't learn about that at Alfred; although you may have
> learned that copper in lead based glazes was a no-no. It has been
> known for many decades that copper increased the leaching of lead.
> However, no one worried about the leaching of copper when lead was
so
> much more on their minds. Ron's and my data have shown that copper
is
> difficult to keep in all but the very most stable glazes and, even
> then, 5% is about the maximum they will hold.
>
.
>
> >
>
______________________________________________________________________
________
> Send postings to clayart@...
>
> You may look at the archives for the list or change your
subscription
> settings from http://www.ceramics.org/clayart/
>
> Moderator of the list is Mel Jacobson who may be reached at
melpots@...
>
Ron Roy on sun 7 jan 07
Hi Eleanor,
The ration makes me think it is a matte glaze - in this case an alumina
matte - and it's also high in Strontium. The problem with alumina mattes is
their lack of silica - low silica means unstable in terms of leaching and
durability.
If you add silica to this glaze you make it shiny - and you still gave
about 5% copper - which is a lot.
Looks like the answer in this case is no.
Perhaps taking stable glazes and adding copper to them would be a
productive strategy.
RR
>i was given this glaze by another clayarter. i love it and use it on the
>outside of planters and vases. but when i glazed a test dish and placed a
>lemon slice on it-wow, did it leach color. is there anything i can do to
>make it more stable and still keep the wonderful color. also if i can't
>correct the leaching would it be okay to use it on the outside of
>pitchers, mugs and bowls and then a white liner inside. does anyone see
>anything wrong with that idea.
>here is the glaze and i am sorry i can't remember who gave it to me.
>
>turquoise glaze ^6 oxid
>Nephy. syen. 345
>Strontium carb 130
>Gerstley borate 12
>bentonite 14
>Copper carb 19
>
>this shows a great surface on ^6 porcelain. i made 20 planters for a
>wedding display. would love to b e able to put it to more uses.
>thganks for all your help
Ron Roy
RR#4
15084 Little Lake Road
Brighton, Ontario
Canada
K0K 1H0
Ivor and Olive Lewis on sun 7 jan 07
Dear John Hesselberth,
Good to hear from you again. A Happy New Year to you. Hope you have a =
great time in 2007.
You say <leaching by adding the copper to a stable base glaze vs an unstable =
one.>>
Great ! So what are the properties that define Glaze Stability ? Are =
stable glazes defined by their ability to retain additives that colour =
them ? Are they defined by their ability to remain vitrified or resist =
devitrification ? Are compositions know to have soluble elements =
(derivatives of Group 1 Metals ) in them thought of as being stable ?=20
I wonder if an exploration of the making of Ceramic Molecular Sieves =
might give us some clues?
Regarding Rutile (TiO2). This seems to be a very active material and =
features in a considerable number of Phase Diagrams that would be of =
interest to Potters. As they say, if the temperature is right, it will =
become an ingredient in the melt. Alas, I cannot afford three grand for =
the most recent edition of the PD collection so without that all I can =
say is that I have not been able to find a compound or diagram that will =
couple Copper and Titanium in a ceramic environment. Perhaps as an extra =
variable it ought to be excluded from experiments relating to the =
dissolution of glaze samples.
Good to do some thinking and searching.
Must go and check the kiln. first cool day of the year, and a damp one =
as well !
Best regards,
Ivor
Edouard Bastarache Inc. on mon 8 jan 07
Hi John,
thanks.
I asked this question because many years ago we
had
a heated discussion here on the safety of
zirconium-
encapsulated cadmium, and it was suggested by many
to add zirconium silicate to the glazes containing
this
new presentation of cad mium pigments in order to
be
more on the safe side.
So I thought the same could be good for
copper-containung
glazes.
Later,
Edouard Bastarache
Le Français Volant
The Flying Frenchman
Sorel-Tracy
Quebec
www.sorel-tracy.qc.ca/~edouardb/Welcome.html
http://perso.wanadoo.fr/smart2000/index.htm
http://www.pshcanada.com/Toxicology.htm
www.thepottersshop.blogspot.com
http://www.ceramique.com/cerambooks/rayons/technologie.php
http://www.flickr.com/photos/30058682@N00/
John Hesselberth on mon 8 jan 07
On Jan 6, 2007, at 8:18 PM, Ivor and Olive Lewis wrote:
> Great ! So what are the properties that define Glaze Stability ?
> Are stable glazes defined by their ability to retain additives that
> colour them ? Are they defined by their ability to remain vitrified
> or resist devitrification ? Are compositions know to have soluble
> elements (derivatives of Group 1 Metals ) in them thought of as
> being stable ?
Hello Ivor,
When I talk about stability I am usually talking about resistance to
acids since 98% or so of our foods are acidic. But alkaline
resistance is important also during dish washing. A glaze that does
not resist devitrification also releases colorants--I'm not sure
there is any practical difference between the two definitions you
propose. Except for surface-exposed colorants, even those that are
not dissolved in the glass are encased by it and the glass would have
to break down to release them.
As to the effect of alkais, it is well reported that sodium can
reduce glaze stability--lithium and potassium are reported by Singer
and Singer to be an improvement over sodium. You can read their
thoughts on chemical resistance on p 559 and 560 of the English
edition of Industrial Ceramics, ISBN 0 412 06610 7. Other references
are scattered widely through the literature. Not a lot of work has
been done except with respect to stability of lead-based glazes --
and then they were only worrying about the leaching of lead.
Regards,
John
John Hesselberth on mon 8 jan 07
On Jan 5, 2007, at 11:12 PM, Edouard Bastarache Inc. wrote:
> what about adding zirconium silicate intead of
> rutile?
Hi Edouard,
I need to correct my response to this. Ron reminded me that we did do
some experimentation with zirconium silicate. Contrary to a couple
references in the literature, our data showed more copper leaching
with zirconium silicate than with none. So it was the exact opposite
of rutile. There were only few data points so I would not be ready
to make a big deal of it, but that was the result we got.
Regards,
John
Ivor and Olive Lewis on tue 9 jan 07
Dear John Hesselberth,=20
Thanks for your explanation.
You then mean Corrosion Resistance or the lack thereof. That is =
resistance or lack of resistance to chemical attack which will dissolve =
material. Singer and Singer, in the ref you give, give it the heading =
"Chemical Resistance"
It has nothing to do with the "Self Destruction" that can occur due to =
post firing phase changes such as might be expected from delayed phase =
changes that cause volumetric changes or the precipitation of mineral =
species.
I'm glad to have that confusion cleared.
Best regards,
Ivor.
| |
|
