Calista Bookout on sun 24 feb 02
If you wish to decorate with oxides such as copper, iron or cobalt
must the decoration be applied under the glaze, assuming that the
glaze itself is food safe and stable or can you apply the oxides over
the glaze and have it safely enter into the glaze melt?
This question is from a potter who is not a clayart member, but a
friend of mine. Thanks in advance for this information.
C.C. Bookout
Martin Howard on mon 25 feb 02
I would always put the colouring oxide in the slip, under the clear glaze.
That way you should always be safe.
But there may well be different views on this.
Martin Howard
Webbs Cottage Pottery
Woolpits Road, Great Saling
BRAINTREE, Essex CM7 5DZ
01371 850 423
martin@webbscottage.co.uk
http://www.webbscottage.co.uk
Updated 8th February 2002
John Hesselberth on mon 25 feb 02
Hi Calista,
No you cannot assume this. The only way to know is to test. Not only might
safety be a concern, but durability certainly will. Will a piece like this
hod up to multiple passes through a dishwasher? No one knows without
testing. Even putting the oxides under a clear glaze may not do the job
depending on the amount and type of oxide present and the thickness and
durability of the clear glaze. Test, test, test.....
Regards,
John
on 2/24/02 8:09 PM, Calista Bookout at claylady@OPTONLINE.NET wrote:
> If you wish to decorate with oxides such as copper, iron or cobalt
> must the decoration be applied under the glaze, assuming that the
> glaze itself is food safe and stable or can you apply the oxides over
> the glaze and have it safely enter into the glaze melt?
>
> This question is from a potter who is not a clayart member, but a
> friend of mine. Thanks in advance for this information.
>
> C.C. Bookout
>
> ______________________________________________________________________________
> 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.
Web sites: http://www.masteringglazes.com and http://www.frogpondpottery.com
Email: john@frogpondpottery.com
"The life so short, the craft so long to learn." Chaucer's translation of
Hippocrates, 5th cent. B.C.
Ron Roy on tue 26 feb 02
The best way to deal with this situation is to find a stable glaze - clear
and stable - mix any oxides with this glaze - say 50/50 - then put a clear
stable glaze that does not craze over the decoration.
If the decoration is going to be where food will be in contact with it -
then have it tested for metal release.
Above all - make sure everything resists the vinegar test - but I still
recommend lab testing.
I know many potters (I should say most) think that a stable glaze is hard
to make - it is not - if you know what to look for. Trouble is - up till
now we did not know what to look for.
RR
>If you wish to decorate with oxides such as copper, iron or cobalt
>must the decoration be applied under the glaze, assuming that the
>glaze itself is food safe and stable or can you apply the oxides over
>the glaze and have it safely enter into the glaze melt?
>
>This question is from a potter who is not a clayart member, but a
>friend of mine. Thanks in advance for this information.
>
>C.C. Bookout
Ron Roy
RR# 4
15084 Little Lake Rd..
Brighton,
Ontario, Canada
KOK 1H0
Residence 613-475-9544
Studio 613-475-3715
Fax 613-475-3513
Randy Blume on wed 27 feb 02
>
> From: Ron Roy
> Date: 2002/02/26 Tue PM 06:38:39 EST
> To: CLAYART@LSV.CERAMICS.ORG
> Subject: Re: food safe oxide decoration
Can anybody tell me how and where to test a glaze for food safeness? How expensive is it ? Randy Blume
> The best way to deal with this situation is to find a stable glaze - clear
> and stable - mix any oxides with this glaze - say 50/50 - then put a clear
> stable glaze that does not craze over the decoration.
>
> If the decoration is going to be where food will be in contact with it -
> then have it tested for metal release.
>
> Above all - make sure everything resists the vinegar test - but I still
> recommend lab testing.
>
> I know many potters (I should say most) think that a stable glaze is hard
> to make - it is not - if you know what to look for. Trouble is - up till
> now we did not know what to look for.
>
> RR
>
> >If you wish to decorate with oxides such as copper, iron or cobalt
> >must the decoration be applied under the glaze, assuming that the
> >glaze itself is food safe and stable or can you apply the oxides over
> >the glaze and have it safely enter into the glaze melt?
> >
> >This question is from a potter who is not a clayart member, but a
> >friend of mine. Thanks in advance for this information.
> >
> >C.C. Bookout
>
> Ron Roy
> RR# 4
> 15084 Little Lake Rd..
> Brighton,
> Ontario, Canada
> KOK 1H0
> Residence 613-475-9544
> Studio 613-475-3715
> Fax 613-475-3513
>
> ______________________________________________________________________________
> 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.
>
Martin Rice on wed 27 feb 02
----- Original Message -----
From: "Ron Roy"
To:
Sent: Tuesday, February 26, 2002 5:38 PM
Subject: Re: [CLAYART] food safe oxide decoration
> Above all - make sure everything resists the vinegar test - but I still
> recommend lab testing.
I've seen reference to the "vinegar test" on the list before. Could someone
tell me what it is?
Thanks,
Martin
Lagunas de Barú, Costa Rica
www.rice-family.org
John Hesselberth on wed 27 feb 02
on 2/27/02 5:02 PM, Martin Rice at martin@RICE-FAMILY.ORG wrote:
> I've seen reference to the "vinegar test" on the list before. Could someone
> tell me what it is?
Hi Martin,
Soaking 1/2 of a test tile for 3 days in household vinegar (normally 5%
acetic acid) can be a qualitative indication of glaze stability, i.e. it can
weed out really bad glazes--it cannot tell you how good a glaze is. After 3
days you rinse the sample, let it air dry thoroughly and examine it closely.
If the part immersed in vinegar has changed color you have a very unstable
glaze that is not suitable for functional work. If the sheen of the glaze
changes but the color does not, the glaze might be stable or it might
not--you have to do further testing to tell. If there is no change in sheen
or color the glaze is fairly stable, but you still have to quantitatively
leach test it to really know what you have.
Overall it is an excellent first screening test to help you eliminate the
worst glazes.
Regards,
John
Web sites: http://www.masteringglazes.com and http://www.frogpondpottery.com
Email: john@frogpondpottery.com
"Art is not a handicraft, it is the transmission of feeling the artist has
experienced." Leo Tolstoy, 1898
John Hesselberth on thu 28 feb 02
Hi Randy,
You can read how to leach test and what it cost on my web site at
http://www.frogpondpottery.com/glazetest.html
There are other pages on the site which talk about interpretation of
results. There is also a significant section on the subject in the book Ron
Roy and I have written. If you are interested in that go
http://www.masteringglazes.com/
Regards,
John
on 2/27/02 11:15 PM, Randy Blume at randy@HANDSONCLAY.COM wrote:
>>
>> From: Ron Roy
>> Date: 2002/02/26 Tue PM 06:38:39 EST
>> To: CLAYART@LSV.CERAMICS.ORG
>> Subject: Re: food safe oxide decoration
>
>
> Can anybody tell me how and where to test a glaze for food safeness? How
> expensive is it ? Randy Blume
>
Web sites: http://www.masteringglazes.com and http://www.frogpondpottery.com
Email: john@frogpondpottery.com
"Art is not a handicraft, it is the transmission of feeling the artist has
experienced." Leo Tolstoy, 1898
| |
|
