Lee on mon 5 sep 11
On Mon, Sep 5, 2011 at 4:18 PM, Mike wrote:
> If it tests negative for leaching, why not use it on the inside?
When I get the space, I want to try oribe in a birdbath, to see if it
reduces algae, like Grandma's copper pennies.
--
=3DA0Lee Love in Minneapolis
http://mingeisota.blogspot.com/
=3DA0"Ta tIr na n-=3DF3g ar chul an tI=3D97tIr dlainn trina ch=3DE9ile"=3D9=
7that is, =3D
"The
land of eternal youth is behind the house, a beautiful land fluent
within itself." -- John O'Donohue
Randall Moody on mon 5 sep 11
On Mon, Sep 5, 2011 at 11:25 AM, Nancy Jervey wrote:
> Because I am using 6.54 % copper carb. I am assuming that is not a food
> safe glaze.
>
You should test this for leaching before you make a decision. No reason to
assume that it would be an issue. Many things are said to be problems or
"toxic" with little to no scientific data to back it up.
--
Randall in Atlanta
http://wrandallmoody.com
Nancy Jervey on mon 5 sep 11
I know I cannot use an Oribe glaze on the inside of a piece, but is it ok=
=3D
to have the=3D20
orbibe glaze on the rim of a mug?
Thanks,
Nancy
Randall Moody on mon 5 sep 11
On Mon, Sep 5, 2011 at 7:33 AM, Nancy Jervey wrote:
> I know I cannot use an Oribe glaze on the inside of a piece, but is it ok
> to have the
> orbibe glaze on the rim of a mug?
> Thanks,
> Nancy
>
Why would you think that you can't use an Oribe glaze inside of a piece?
--
Randall in Atlanta
http://wrandallmoody.com
Nancy Jervey on mon 5 sep 11
I guess because I am using 6.5% copper carb in the glaze. I figured that =
=3D
amount of=3D20
copper was not food safe.
Nancy
Nancy Jervey on mon 5 sep 11
Because I am using 6.54 % copper carb. I am assuming that is not a food s=
=3D
afe glaze.
John Hesselberth on tue 6 sep 11
>>=3D20
>> Because I am using 6.54 % copper carb. I am assuming that is not a =3D
food
>> safe glaze.
>>=3D20
>=3D20
> You should test this for leaching before you make a decision. No =3D
reason to
> assume that it would be an issue. Many things are said to be problems =3D
or
> "toxic" with little to no scientific data to back it up.
Hi Nancy,=3D20
I have tested many copper-containing glazes over the years and have =3D
never found one that had more than 5% copper carbonate in it that would =3D
not leach substantial quantities of copper. The water standard for =3D
copper is 2 ppm; I personally think that is too strict for pottery and =3D
set my own goal at 6 ppm. The Oribes I have tested have leached in the =3D
30-60 ppm range. They need 6% or more copper carbonate to get that =3D
metallic sheen that people like. There may be a better one some place, =3D
but I haven't found it.
As for trying it in a bird bath as one person suggested, it may well =3D
keep the algae under control, but you will never know how many birds die =
=3D
or are made ill because they won't die on the spot.
As to whether or not to put it on the rim of a food vessel, you will =3D
have to decide that yourself. There certainly is no law or regulation I =3D
am aware of that would guide you.
Regards,
John=3D
Mike on tue 6 sep 11
If it tests negative for leaching, why not use it on the inside?
Mike
in Taku, Japan
http://karatsupots.com
http://karatsupots.blogspot.com
Workshop in Taku 2012: The Simple Teabowl, May 12 - 18
http://karatsupots.com/workshop2012/2012home.html
http://workshopintaku2012.blogspot.com/
(2011/09/05 20:33), Nancy Jervey wrote:
> I know I cannot use an Oribe glaze on the inside of a piece, but is it ok=
to have the
> orbibe glaze on the rim of a mug?
> Thanks,
> Nancy
>
Steve Slatin on tue 6 sep 11
Nancy --
Unbeknownst to you, your first message landed directly
in the middle of a long-standing battle on ClayArt.
There is a large group of people here who tread on the
side of caution, who would argue that most glazes with
over two percent of copper in them will tend to leach,
and leaching glazes are inherently untrustworthy.
There is a second group who tread on the other side,
who will argue, variously, that with most uses there
isn't much leaching, even with a glaze that may leach,
or you should just do a home-test and if it holds up
for 15 minutes or so, what's the big deal anyway,
or leaching copper is good-good-good because copper
is an essential nutrient, or "the ancients didn't
worry about leaching, so why should we?" or even "I'm
a potter, I'm poor as a church mouse, so wadda-ya-
gonna-do, sue me?
If you are concerned with glaze stability, test it --
my own experience is that every glaze I tried with
3% copper or more did, in fact, leach, leaving a
visibly different glaze surface behind, and I know
my home test is unequal to a laboratory test.
If you are satisfied with your own test, then spring
for a lab test and find out what leaching actually
does occur.
Or, you could dip the vessel upright into the copper-
rich glaze, stopping a half-inch or so below the rim,
and glaze the inside, lip and rim with a glaze with
nothing in it that might be serious even if it did
leach. That's what I do, and it's simple and cheap
and I don't need to worry about my clients coming
back complaining that I made them ill.
Steve Slatin --
N48.0886450
W123.1420482
--- On Mon, 9/5/11, Nancy Jervey wrote:
> I guess because I am using 6.5%
> copper carb in the glaze. I figured that amount of
> copper was not food safe.
> Nancy
>
Ron Roy on tue 6 sep 11
Hi Nancy,
I have analyzed many Oribe glazes and they were all short of silica
which means they are unstable to begin with. That means they will
leach with acid foods.
They are all oversupplied with copper - in fact - I've heard that
potters sometimes scrub off the black copper that comes to the surface
as the glaze cools.
You can be sure that such glazes leach enough copper to change the
taste of food in a relatively short time.
I don't think that we can call such a glaze unsafe - although there
are some people who cannot tolerate any copper - and some already get
copper in their water - and there is an upper limit to how much your
body can deal with.
I think you are right to be concerned about using such glazes as
liners - who needs their orange juice or other foods to test of copper?
As to below the lip - perhaps you could do an experiment - use your
own taste buds - just suck on an oribe glaze and see how long it takes
to taste the copper.
RR
Quoting Nancy Jervey :
> I know I cannot use an Oribe glaze on the inside of a piece, but is
> it ok to have the
> orbibe glaze on the rim of a mug?
> Thanks,
> Nancy
>
Steve Mills on wed 7 sep 11
Unlikely, especially at stoneware temps.=3D20
Steve M
Steve Mills
Bath
UK
www.mudslinger.me.uk
Sent from my Ipod touch
On 6 Sep 2011, at 02:18, Lee wrote:
> On Mon, Sep 5, 2011 at 4:18 PM, Mike wrote:
>> If it tests negative for leaching, why not use it on the inside?
>=3D20
> When I get the space, I want to try oribe in a birdbath, to see if it
> reduces algae, like Grandma's copper pennies.
>=3D20
> --
> Lee Love in Minneapolis
> http://mingeisota.blogspot.com/
>=3D20
> "Ta tIr na n-=3DC3=3DB3g ar chul an tI=3DE2=3D80=3D94tIr dlainn trina ch=
=3DC3=3DA9ile"=3DE2=3D
=3D80=3D94that is, "The
> land of eternal youth is behind the house, a beautiful land fluent
> within itself." -- John O'Donohue
Edouard Bastarache on wed 7 sep 11
My Oribe Green Glaze :
http://www.flickr.com/photos/potier/102899351/in/photostream
Gis,
Edouard Bastarache
Spertesperantisto
Sorel-Tracy
Quebec
http://www.flickr.com/photos/30058682@N00/
http://edouardbastarache.blogspot.com/
http://edouardbastaracheblogs2.blogspot.com/
http://www.facebook.com/edouard.bastarache
Mike on wed 7 sep 11
Well, I wasn't wrong about my memory. Here is the correct recipe, since
the one below turned out to be quite wrong:
Ersatz Oribe, Cone 9-11
Wood Ash 5
Silica 4
Kamado Spar 4
Red Ochre-like stuff 3.5
+ 4-5% copper oxide
Mike
Mike
in Taku, Japan
http://karatsupots.com
http://karatsupots.blogspot.com
Workshop in Taku 2012: The Simple Teabowl, May 12 - 18
http://karatsupots.com/workshop2012/2012home.html
http://workshopintaku2012.blogspot.com/
(2011/09/07 12:11), Mike wrote:
> While I won't say anything about the positions Steve outlines below, I
> will say that my 'ersatz oribe' green is something like:
> Wood ash 5
> Silica 3
> Red Ochre-like stuff 3 (high in alumina?)
> Kamado Feldspar 4
> + 4-5% copper oxide
> Fire to cone 9-11, oxidation
>
> I may not have this just right, since my glaze notes are in the shop
> right now (I can't get in to check because of some wet concrete) and
> my memory is notoriously bad. I'll check later, and if it's wrong,
> I'll post a correction.
>
> Anyway, I haven't done a lab test of this glaze for leaching yet, but
> I have left it on the counter in straight lemon juice for several
> days, with no visible change (naked eye and loupe) in the glaze surface.
>
> Sorry, I don't have analysis info for the wood ash or the red
> ochre-like stuff, it is not store bought and changes from batch to
> batch anyway, so adjustments are necessary from time to time.
>
> This glaze does form a bit of an oxide layer in the firing, which then
> needs some cleaning later. See:
>
> http://karatsupots.com/wordpress/2011/07/washing-your-oribe.html
>
> This is not a true oribe green, in the Japanese sense of the name.
> Most oribe greens here are cone 6 (roughly) oxidation glazes.
>
> All the best,
>
> Mike
>
> Mike
> in Taku, Japan
>
> http://karatsupots.com
> http://karatsupots.blogspot.com
>
> Workshop in Taku 2012: The Simple Teabowl, May 12 - 18
>
> http://karatsupots.com/workshop2012/2012home.html
>
> http://workshopintaku2012.blogspot.com/
>
> (2011/09/07 2:12), Steve Slatin wrote:
>> Nancy --
>>
>> Unbeknownst to you, your first message landed directly
>> in the middle of a long-standing battle on ClayArt.
>>
>> There is a large group of people here who tread on the
>> side of caution, who would argue that most glazes with
>> over two percent of copper in them will tend to leach,
>> and leaching glazes are inherently untrustworthy.
>>
>> There is a second group who tread on the other side,
>> who will argue, variously, that with most uses there
>> isn't much leaching, even with a glaze that may leach,
>> or you should just do a home-test and if it holds up
>> for 15 minutes or so, what's the big deal anyway,
>> or leaching copper is good-good-good because copper
>> is an essential nutrient, or "the ancients didn't
>> worry about leaching, so why should we?" or even "I'm
>> a potter, I'm poor as a church mouse, so wadda-ya-
>> gonna-do, sue me?
>>
>> If you are concerned with glaze stability, test it --
>> my own experience is that every glaze I tried with
>> 3% copper or more did, in fact, leach, leaving a
>> visibly different glaze surface behind, and I know
>> my home test is unequal to a laboratory test.
>>
>> If you are satisfied with your own test, then spring
>> for a lab test and find out what leaching actually
>> does occur.
>>
>> Or, you could dip the vessel upright into the copper-
>> rich glaze, stopping a half-inch or so below the rim,
>> and glaze the inside, lip and rim with a glaze with
>> nothing in it that might be serious even if it did
>> leach. That's what I do, and it's simple and cheap
>> and I don't need to worry about my clients coming
>> back complaining that I made them ill.
>>
>> Steve Slatin --
>>
>> N48.0886450
>> W123.1420482
>>
>>
>> --- On Mon, 9/5/11, Nancy Jervey wrote:
>>
>>> I guess because I am using 6.5%
>>> copper carb in the glaze. I figured that amount of
>>> copper was not food safe.
>>> Nancy
>>>
inge nielsen on wed 7 sep 11
Hi Nancy, John,
I am aware you work in the US, but speaking of laws and regulations, the EU
has rules for pottery glazes and leaching thereof (No. 2023/2006 of 22
December 2006, among others)... and Denmark, where I am from, has an
additional law that the rim of drinking vessels (area where the mouth comes
into contact with the piece) must also test free of leaching material.
You don't have such rules in the US?
Best regards,
Inge
www.mypottery.blog.com
On Tue, Sep 6, 2011 at 8:35 PM, John Hesselberth w=
rote:
> >>
> >> Because I am using 6.54 % copper carb. I am assuming that is not a foo=
d
> >> safe glaze.
> >>
> >
> > You should test this for leaching before you make a decision. No reason
> to
> > assume that it would be an issue. Many things are said to be problems o=
r
> > "toxic" with little to no scientific data to back it up.
>
> Hi Nancy,
>
> I have tested many copper-containing glazes over the years and have never
> found one that had more than 5% copper carbonate in it that would not lea=
ch
> substantial quantities of copper. The water standard for copper is 2 ppm;=
I
> personally think that is too strict for pottery and set my own goal at 6
> ppm. The Oribes I have tested have leached in the 30-60 ppm range. They n=
eed
> 6% or more copper carbonate to get that metallic sheen that people like.
> There may be a better one some place, but I haven't found it.
>
> As for trying it in a bird bath as one person suggested, it may well keep
> the algae under control, but you will never know how many birds die or ar=
e
> made ill because they won't die on the spot.
>
> As to whether or not to put it on the rim of a food vessel, you will have
> to decide that yourself. There certainly is no law or regulation I am awa=
re
> of that would guide you.
>
> Regards,
>
> John
Mike on wed 7 sep 11
While I won't say anything about the positions Steve outlines below, I
will say that my 'ersatz oribe' green is something like:
Wood ash 5
Silica 3
Red Ochre-like stuff 3 (high in alumina?)
Kamado Feldspar 4
+ 4-5% copper oxide
Fire to cone 9-11, oxidation
I may not have this just right, since my glaze notes are in the shop
right now (I can't get in to check because of some wet concrete) and my
memory is notoriously bad. I'll check later, and if it's wrong, I'll
post a correction.
Anyway, I haven't done a lab test of this glaze for leaching yet, but I
have left it on the counter in straight lemon juice for several days,
with no visible change (naked eye and loupe) in the glaze surface.
Sorry, I don't have analysis info for the wood ash or the red ochre-like
stuff, it is not store bought and changes from batch to batch anyway, so
adjustments are necessary from time to time.
This glaze does form a bit of an oxide layer in the firing, which then
needs some cleaning later. See:
http://karatsupots.com/wordpress/2011/07/washing-your-oribe.html
This is not a true oribe green, in the Japanese sense of the name. Most
oribe greens here are cone 6 (roughly) oxidation glazes.
All the best,
Mike
Mike
in Taku, Japan
http://karatsupots.com
http://karatsupots.blogspot.com
Workshop in Taku 2012: The Simple Teabowl, May 12 - 18
http://karatsupots.com/workshop2012/2012home.html
http://workshopintaku2012.blogspot.com/
(2011/09/07 2:12), Steve Slatin wrote:
> Nancy --
>
> Unbeknownst to you, your first message landed directly
> in the middle of a long-standing battle on ClayArt.
>
> There is a large group of people here who tread on the
> side of caution, who would argue that most glazes with
> over two percent of copper in them will tend to leach,
> and leaching glazes are inherently untrustworthy.
>
> There is a second group who tread on the other side,
> who will argue, variously, that with most uses there
> isn't much leaching, even with a glaze that may leach,
> or you should just do a home-test and if it holds up
> for 15 minutes or so, what's the big deal anyway,
> or leaching copper is good-good-good because copper
> is an essential nutrient, or "the ancients didn't
> worry about leaching, so why should we?" or even "I'm
> a potter, I'm poor as a church mouse, so wadda-ya-
> gonna-do, sue me?
>
> If you are concerned with glaze stability, test it --
> my own experience is that every glaze I tried with
> 3% copper or more did, in fact, leach, leaving a
> visibly different glaze surface behind, and I know
> my home test is unequal to a laboratory test.
>
> If you are satisfied with your own test, then spring
> for a lab test and find out what leaching actually
> does occur.
>
> Or, you could dip the vessel upright into the copper-
> rich glaze, stopping a half-inch or so below the rim,
> and glaze the inside, lip and rim with a glaze with
> nothing in it that might be serious even if it did
> leach. That's what I do, and it's simple and cheap
> and I don't need to worry about my clients coming
> back complaining that I made them ill.
>
> Steve Slatin --
>
> N48.0886450
> W123.1420482
>
>
> --- On Mon, 9/5/11, Nancy Jervey wrote:
>
>> I guess because I am using 6.5%
>> copper carb in the glaze. I figured that amount of
>> copper was not food safe.
>> Nancy
>>
Steve Mills on wed 7 sep 11
So far (unless I missed it) I've read no indications as to what temperature=
s=3D
the correspondents on this thread are firing.=3D20
As I understand it, glaze final temperature as well as composition has a lo=
t=3D
to do with whether or not Oxide leaching can take place.=3D20
Obviously if copper in any concentration is used at earthenware temperature=
s=3D
, particularly if the glaze contains any sort of lead compound (because it =
p=3D
romotes lead release), has to be avoided or at least treated with care, bu=
t=3D
does the same apply to stoneware glazes.=3D20
I habitually fire to cone 9+ gas 11+ with wood, and as far as information
available to me indicates the only material/glaze I personally needed to av=
o=3D
id in my production is/are Barium and Barium Matt (which I never liked anyw=
a=3D
y!). This is as a result of being responsible for MSDS production at our Co=
m=3D
pany; Bath Potters Supplies.=3D20
So where in the stoneware temperature range does the oxide "problem" arise?=
=3D20=3D
For example; Steve, you say you are experiencing leaching, what are you fir=
i=3D
ng to?
John, what temperatures are your findings based on?
Steve M
AKA Curious of Bath. UK
Steve Mills
Bath
UK
www.mudslinger.me.uk
Sent from my Ipod touch
On 6 Sep 2011, at 18:12, Steve Slatin wrote:
> Nancy --
>=3D20
> Unbeknownst to you, your first message landed directly
> in the middle of a long-standing battle on ClayArt.
>=3D20
> There is a large group of people here who tread on the
> side of caution, who would argue that most glazes with
> over two percent of copper in them will tend to leach,
> and leaching glazes are inherently untrustworthy.
>=3D20
> There is a second group who tread on the other side,
> who will argue, variously, that with most uses there
> isn't much leaching, even with a glaze that may leach,
> or you should just do a home-test and if it holds up
> for 15 minutes or so, what's the big deal anyway,
> or leaching copper is good-good-good because copper
> is an essential nutrient, or "the ancients didn't
> worry about leaching, so why should we?" or even "I'm
> a potter, I'm poor as a church mouse, so wadda-ya-
> gonna-do, sue me?
>=3D20
> If you are concerned with glaze stability, test it --
> my own experience is that every glaze I tried with
> 3% copper or more did, in fact, leach, leaving a
> visibly different glaze surface behind, and I know
> my home test is unequal to a laboratory test.
>=3D20
> If you are satisfied with your own test, then spring
> for a lab test and find out what leaching actually
> does occur.
>=3D20
> Or, you could dip the vessel upright into the copper-
> rich glaze, stopping a half-inch or so below the rim,
> and glaze the inside, lip and rim with a glaze with
> nothing in it that might be serious even if it did
> leach. That's what I do, and it's simple and cheap
> and I don't need to worry about my clients coming
> back complaining that I made them ill.
>=3D20
> Steve Slatin --
>=3D20
> N48.0886450
> W123.1420482
>=3D20
>=3D20
> --- On Mon, 9/5/11, Nancy Jervey wrote:
>=3D20
>> I guess because I am using 6.5%
>> copper carb in the glaze. I figured that amount of
>> copper was not food safe.
>> Nancy
>>=3D20
John Hesselberth on wed 7 sep 11
On Sep 6, 2011, at 11:52 PM, inge nielsen wrote:
> You don't have such rules in the US?
Hi Inge,
Only for lead and cadmium in the U.S. Do your rules give limits or just =3D
state 'free of leachables'? If the latter, no glaze will pass. Every =3D
glaze leaches a little bit of something depending on the aggressiveness =3D
of the leaching test.
Regards,
John=3D
John Hesselberth on wed 7 sep 11
On Sep 7, 2011, at 7:01 AM, Steve Mills wrote:
> So where in the stoneware temperature range does the oxide "problem" =3D
arise?
Hi Steve,
It arises at any temperature if the glaze is not well balanced. Higher =3D
temperature cannot compensate for a poorly formulated glaze, e.g. low =3D
silica or alumina as Ron Roy has pointed out. But even with a well =3D
formulated glaze, copper is the most difficult of all the colorants we =3D
commonly use to keep in a glaze. As I said in an earlier message when =3D
the amount of copper carbonate goes above 5% the leaching starts to =3D
increase exponentially. Of course if a glaze is not thoroughly melted =3D
during firing, the leaching is even worse. Unfortunately, a lot of matte =
=3D
glazes in the literature are "unmelted mattes". That is they get their =3D
matte surface by never completely melting the mixture of ingredients so =3D
they don't form "good glass".
Regards,
John
John Hesselberth on wed 7 sep 11
On Sep 7, 2011, at 7:01 AM, Steve Mills wrote:
> John, what temperatures are your findings based on?
Sorry I didn't answer this. Most of my results are at cone 6, but I have =
=3D
tested quite a number of cone 10 glazes fired to cone 10. Same =3D
conclusions. Pure temperature has little to do with the phenomena. =3D
Proper glaze formulation and thorough melting during firing are the =3D
important variables--plus colorant concentration.
John
=3D20=3D
John Britt on wed 7 sep 11
Inge,
If you don't mind, what are the laws about leaching, e.g. what materials =
=3D
are=3D20
outlawed.
=3D20
If it is not too much trouble.
Johnbrittpottery.com
Steve Slatin on wed 7 sep 11
Mike -- I wasn't trying to say that my experience
constitutes a standard -- only that it's my experience.
What do you mean by "Red Ochre-like stuff?" Is it
some local material you found, or a commercial product
of some kind?
Steve Slatin --
N48.0886450
W123.1420482
--- On Tue, 9/6/11, Mike wrote:
> While I won't say anything about the
> positions Steve outlines below, I
> will say that my 'ersatz oribe' green is something like:
> Wood ash 5
> Silica 3
> Red Ochre-like stuff 3 (high in alumina?)
> Kamado Feldspar 4
> + 4-5% copper oxide
> Fire to cone 9-11, oxidation
>
Steve Slatin on wed 7 sep 11
I mostly fire to ^6 ox, but last winter did ^10 r -- I did
home testing of a few high-copper glazes and found the same
problem, but I didn't have any tested that were above 1.5%
and below 4%.
I'm not sure how much difference the temperature of maturation
is compared to the structure of the glass -- if it has enough
silica to form the extremely large structures characteristic
of glass, and sufficient alumina to create the structural rigidity
we prize.
Steve Slatin --=3D20
N48.0886450
W123.1420482
--- On Wed, 9/7/11, Steve Mills wrote:
> From: Steve Mills
> Subject: Re: Food safe rim
> To: Clayart@LSV.CERAMICS.ORG
> Date: Wednesday, September 7, 2011, 4:01 AM
> So far (unless I missed it) I've read
> no indications as to what temperatures the correspondents on
> this thread are firing.=3D20
> As I understand it, glaze final temperature as well as
> composition has a lot to do with whether or not Oxide
> leaching can take place.=3D20
> Obviously if copper in any concentration is used at
> earthenware temperatures, particularly if the glaze contains
> any sort of lead compound (because it promotes lead
> release),=3DA0 has to be avoided or at least treated with
> care, but does the same apply to stoneware glazes.=3D20
> I habitually fire to cone 9+ gas 11+ with wood, and as far
> as information
> available to me indicates the only material/glaze I
> personally needed to avoid in my production is/are Barium
> and Barium Matt (which I never liked anyway!). This is as a
> result of being responsible for MSDS production at our
> Company; Bath Potters Supplies.=3D20
> So where in the stoneware temperature range does the oxide
> "problem" arise?=3D20
> For example; Steve, you say you are experiencing leaching,
> what are you firing to?
> John, what temperatures are your findings based on?
>=3D20
> Steve M
> AKA Curious of Bath. UK
>=3D20
> Steve Mills
> Bath
> UK
> www.mudslinger.me.uk
> Sent from my Ipod touch
>=3D20
> On 6 Sep 2011, at 18:12, Steve Slatin
> wrote:
>=3D20
> > Nancy --
> >=3D20
> > Unbeknownst to you, your first message landed
> directly
> > in the middle of a long-standing battle on ClayArt.
> >=3D20
> > There is a large group of people here who tread on
> the
> > side of caution, who would argue that most glazes
> with
> > over two percent of copper in them will tend to
> leach,
> > and leaching glazes are inherently untrustworthy.
> >=3D20
> > There is a second group who tread on the other side,
> > who will argue, variously, that with most uses there
> > isn't much leaching, even with a glaze that may
> leach,
> > or you should just do a home-test and if it holds up
> > for 15 minutes or so, what's the big deal anyway,
> > or leaching copper is good-good-good because copper
> > is an essential nutrient, or "the ancients didn't
> > worry about leaching, so why should we?" or even "I'm
> > a potter, I'm poor as a church mouse, so wadda-ya-
> > gonna-do, sue me?
> >=3D20
> > If you are concerned with glaze stability, test it --
> > my own experience is that every glaze I tried with
> > 3% copper or more did, in fact, leach, leaving a
> > visibly different glaze surface behind, and I know
> > my home test is unequal to a laboratory test.
> >=3D20
> > If you are satisfied with your own test, then spring
> > for a lab test and find out what leaching actually
> > does occur.
> >=3D20
> > Or, you could dip the vessel upright into the copper-
> > rich glaze, stopping a half-inch or so below the rim,
> > and glaze the inside, lip and rim with a glaze with
> > nothing in it that might be serious even if it did
> > leach.=3DA0 That's what I do, and it's simple and
> cheap
> > and I don't need to worry about my clients coming
> > back complaining that I made them ill.
> >=3D20
> > Steve Slatin --
> >=3D20
> > N48.0886450
> > W123.1420482
> >=3D20
> >=3D20
> > --- On Mon, 9/5/11, Nancy Jervey
> wrote:
> >=3D20
> >> I guess because I am using 6.5%
> >> copper carb in the glaze. I figured that amount
> of
> >> copper was not food safe.
> >> Nancy
> >>=3D20
>
Nancy Jervey on thu 8 sep 11
I had a typo in my recipe. Sorry.
That was
EPK 11.73
Thanks,
Nancy
Nancy Jervey on thu 8 sep 11
Here is the glaze recipe that I am using for my oribe glaze. I do not get=
=3D
any copper=3D20
residue after firing to cone 10 in a reduction atmosphere. I plan to do t=
=3D
he lemon test and=3D20
I am looking up a lab to send this glaze off to be tested. If anyone has =
=3D
a suggestion=3D20
which lab I would be grateful.
Here is the glaze. I do not know if there is enough silica to suggest thi=
=3D
s glaze may be=3D20
food safe (at least at the rim). How can I tell that?
Bone ash .98
Talc 7.3
Whiting 20.9
Custer 28.89
Elk 11.73
Flint 23.66
Copper carb 6.54
I use this on stoneware with a porcelain slip applied on the stoneware. A=
=3D
nd then the oribe=3D20
glaze.=3D20
Thanks for all the help.
Nancy
David Woof on thu 8 sep 11
Hi John=3D2C All....Everyone=3D2C
Not singling out anyone's post=3D3B just responding to the general question=
=3D
=3D2C and urging use of common sense questions to ask and consider.
questions=3D3B as in how many hours per day would one have to sit and lick =
or=3D
suck on the rim of a bowl or drinking vessel before enough of anything rea=
=3D
lly dangerous leached from the glaze.(should I swab vinegar on my lips when=
=3D
I try this?) =3DA0=3D20
I don't ever use a saturated copper glaze as a liner in anything even remot=
=3D
ely possible to be used as a food container but I also try to stay real and=
=3D
balanced as I ask why i do=3D2C think=3D2C or believe anything.=3DA0 I do =
my own=3D
testing=3D2C have seen glaze surfaces of unstable saturated copper glazes =
pi=3D
tted and ruined from repeated contacts with acid foods and Automatic dishwa=
=3D
shers and while I am not so concerned with my personal safety from casual f=
=3D
ood contact=3D2C=3DA0 I am deeply concerned with the needs=3D2C safety and =
possib=3D
le fears of the folks who buy and use my work and so do not use copper and =
=3D
the other oxides we "know" to be toxic as liner glazes. Always think of the=
=3D
kids who let orange juice sit all day behind the sofa in their barium glaz=
=3D
e lined sippy cup.=3D20
****Perhaps someone qualified to speak would like to post regarding the dif=
=3D
ferences and toxicity in the various forms of copper=3D2C and under what co=
nd=3D
itions toxicity of concern actually exists.***** We need science facts to s=
=3D
tem this tide!!!
Like why we are creating porous water filtration jars containing added copp=
=3D
er in the clay body=3D2C putting copper pennies in bird baths(are the birds=
f=3D
lying off to die somewhere?) (sheep are reputed to be poisoned by the coppe=
=3D
r in a mineral block that cows seem to thrive on) and copper in our socks t=
=3D
o inhibit various flora and fauna while freaking out about copper in a glaz=
=3D
e on the rim of a pot. While many the world over are cooking in copper kett=
=3D
les=3D2C pots and pans everything from soups to grain mashes for distillati=
on=3D
of alcoholic spirits. =3DA0=3D20
Interestingly but sadly=3D2C the increase of mortality from dysentry=3D2C d=
iarr=3D
eah and other disease has increased in peoples of the world who stopped usi=
=3D
ng their traditional copper cooking pots in favor of "modern developed worl=
=3D
d" vessels.
Let us stay real in our waltz with fear and laws.
Remember that to sustain their bureaucracy and maintain job security=3D3B l=
aw=3D
makers must make laws=3D3B=3DA0 thus are looking for laws to make and here =
on C=3D
layart folks are prattling on about possibly misunderstood facts and unfoun=
=3D
ded fears generated by folk "tales" passed down by personal leaps of "insig=
=3D
ht and belief" or founded on childish enjoyments of shivering around the co=
=3D
llective campfire in the darkness of misinformation.=3DA0=3D20
Save us we plead! And the lawmakers oblige=3D3B trolling everywhere=3D2C in=
clud=3D
ing Clayart=3D2C for ideas=3D2C and "victims" to protect.=3DA0=3D20
Every law made constitutes another loss of a freedom and law makers with no=
=3D
scientific background rely on "expert advice" seasoned liberally with popu=
=3D
lar opinion du jour.=3D20
Let's contribute good science.=3DA0=3DA0 We can start by discerning what we=
rea=3D
lly know as good science vs what possibly twisted desire we harbor to belie=
=3D
ve something simply to support unfounded destructive fears.
David Woof.........trolling for facts=3D2C honesty=3D2C truth and the atten=
dant=3D
personal freedom of life and spirit it supports.
We think with words!=3DA0 What if we replaced guns with dictionaries!=3DA0 =
"The=3D
y" can pry a gun from cold dead fingers but never truth and a life well liv=
=3D
ed.
____________________________________________
2a. Re: Food safe rim
Posted by: "John Britt" johnbrittpottery@GMAIL.COM=3D20
Date: Wed Sep 7=3D2C 2011 1:06 pm ((PDT))
=3D20
Inge=3D2C
=3D20
If you don't mind=3D2C what are the laws about leaching=3D2C e.g. what mate=
rial=3D
s are=3D20
outlawed.
=3D20
=3D20
If it is not too much trouble.
=3D20
Johnbrittpottery.com
=3D20
=3D
Don Goodrich on thu 8 sep 11
Hi Nancy,
John Hesselberth mentions on his frogpondpottery.com website that
Brandywine Science Center (in PA) offers pottery testing.
Their site: http://www.bsclab.com/ has a page with information on their=3D2=
0=3D
services.
The guidelines in Mastering Cone 6 Glazes say that a 10:1 ratio of Sil=
=3D
ica to
Alumina is likely to result in a stable glaze. I don't know if the same a=
=3D
pplies to
cone 10, but no doubt others will give sage advice.
Cheers,
Don Goodrich
Mike on thu 8 sep 11
Hi Steve,
I think I understand what you were getting at, and I didn't take it to
mean your experience constitutes the standard. I just wanted to add my 2
cents without wading around in any of the other sides of the argument
you mentioned.
The red ochre-like stuff is a local material I found, it pops up in
several locations around here and over to Nagasaki, and each location
seems to be a little different. BUT, I realized that it is unnecessary
to worry about it here, as I don't use it in the Oribe glaze, because it
contains too much iron. I was tired when I wrote those mails yesterday
and forgot to exclude it. That recipe with the red ochre is my iron
brown glaze. Drop the red ochre and add some copper oxide for the Ersatz
Oribe.
Interesting aside: my mentor introduced me to the red ochre stuff which
doesn't seem to have an official name. He called it "tsuba-tsuke-ishi",
or "spit (on) rock" because when he was a kid, he and his friends would
spit on it and use it as paint when they played.
One of my other collected materials has the equally technical sounding
name of "gure na yatsu", or "grey stuff".
Anyway, here's the recipe again, without the spit rock:
Ersatz Oribe, Cone 9-11
Wood Ash 5
Silica 4
Kamado Spar 4
+ 4-5% copper oxide
All the best,
Mike
Mike
in Taku, Japan
http://karatsupots.com
http://karatsupots.blogspot.com
Workshop in Taku 2012: The Simple Teabowl, May 12 - 18
http://karatsupots.com/workshop2012/2012home.html
http://workshopintaku2012.blogspot.com/
Liz Gowen 1 on mon 12 sep 11
I also can see the point of liner glazes though my customers don't like =
=3D
it
as much. There are so many nice effects that occur when layering glazes
inside of a bowl. The reason I aquies to this is that folks may store =3D
things
for long periods inside a container. As far as at the lip I have to =3D
agree
the contact time is very limited and unless the glaze is flaking off I =3D
think
it is doubtful it should be an issue. Now if Martha Stewart told you to =3D
take
any ole pot and insert it in another where the lip sit in fluid for days =
=3D
and
is then consumed guess that will have to be on you and Martha, and she =3D
has
much deeper pockets anyway.
I guess I was always surprised when I first went out west ( USA) to
see cliffs whithout guard rails or fences where in the east they seem to =
=3D
be
obsessed with protecting the mentally challanged. The west basically =3D
seems
to say if you are so stupid go ahead and jump, where in the east ohhhhh =3D
but
they may sue. I think we have to find a happy medium or we will be too
scared to make our work. As far as the one size fits all mug handle that
Lily suggested, I can't agree. I don't want an extra large handle for my
personal mugs. I have a small hand and prefer it fit me. Does that mean =3D
my
6ft+ cousins will have a hard time with it perhaps. I live with one size
fits all in many things especially car seats and seat belts that =3D
strangle me
around the neck. But it does work well for the Marboro man. That is why
there is more than 1 way to make a mug. Need to get back to some =3D
clay...Liz
Gowen
questions; as in how many hours per day would one have to sit and lick =3D
or
suck on the rim of a bowl or drinking vessel before enough of anything
really dangerous leached from the glaze.(should I swab vinegar on my =3D
lips
when I try this?) =3DA0=3D20
Ron Roy on tue 13 sep 11
Hi Liz,
A couple of points - the law - regarding lead and cadmium here in =3D20
Canada - and probably elsewhere as well stipulates that those glazes =3D20
have to be a certain distance below the rim if the outside of the ware =3D2=
0
is glazed with a lead or cadmium containing glaze. So that is probably =3D2=
0
where that all came from.
In the case of copper - we are not so much talking about food safe but =3D2=
0
rather - does it change the taste of food or does it discolour.
There are plenty of stable glazes that don't leach much of anything =3D20
into acidic foods - interesting beautiful glazes that can be layered. =3D20
I suspect the real problem that we are dancing around is - how can =3D20
potters tell which glazes are stable - and won't change significantly =3D20
in use.
While there are many who can now make some of those decisions with =3D20
some accuracy - many cannot.
I can help - if there are such questions - all I need is to see a =3D20
recipe in most cases.
Quoting Liz Gowen 1 :
> I also can see the point of liner glazes though my customers don't like =
i=3D
t
> as much. There are so many nice effects that occur when layering glazes
> inside of a bowl. The reason I aquies to this is that folks may store thi=
n=3D
gs
> for long periods inside a container. As far as at the lip I have to agree
> the contact time is very limited and unless the glaze is flaking off I th=
i=3D
nk
> it is doubtful it should be an issue. Now if Martha Stewart told you to t=
a=3D
ke
> any ole pot and insert it in another where the lip sit in fluid for days =
a=3D
nd
> is then consumed guess that will have to be on you and Martha, and she ha=
s
> much deeper pockets anyway.
> questions; as in how many hours per day would one have to sit and lick or
> suck on the rim of a bowl or drinking vessel before enough of anything
> really dangerous leached from the glaze.(should I swab vinegar on my lips
> when I try this?) =3DA0
>
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