Jocelyn McAuley on thu 9 may 02
Hello,
I have some crystal glazes I want to send off for leach tests, as I would
really like to put them inside platter and bowl forms.
Has anyone on the list already tested their macrocrystalline glazes for
leaching? Durability? Were you surprised by the results?
Thanks for your help!
--
Jocelyn McAuley ><<'> jocie@worlddomination.net
Eugene, Oregon http://www.ceramicism.com
John Hesselberth on thu 9 may 02
on 5/9/02 5:12 PM, Jocelyn McAuley at jocie@WORLDDOMINATION.NET wrote:
> Has anyone on the list already tested their macrocrystalline glazes for
> leaching? Durability? Were you surprised by the results?
Hi Jocelyn,
I have seen leaching results from a couple of macrocrystalline glazes that
someone--I've forgotten who now--shared with me. They were better than I
would have predicted. My current guess is that the high level of zinc may
be a factor in achieving those good results. In any case, I'd love to see
your results when you get them. This is a domain of glaze composition where
there is very little hard data. It certainly is outside what I have tested.
Regards,
John
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.
LeRoy Price on fri 10 may 02
Hi Jocelyn:
In addition to glaze leaching, there are two other factors to consider when
using a glaze on a food surface: glaze smoothness, and resistance to
"cutlery" marks.
Since the surfaces of many zinc-silicate crystalline glazes are not
perfectly smooth they tend to catch small particles of food and retain them
even through a washing cycle.
Also these glazes are very frequently "soft." That is, they can be rather
easily marred with an eating utensil.
If the particular glaze you are using has either of these problems, then
using it on a food surface is probably not a good idea.
LeRoy Price
----- Original Message -----
From: "Jocelyn McAuley"
To:
Sent: Thursday, May 09, 2002 2:12 PM
Subject: Crystals- food safe?
> Hello,
>
> I have some crystal glazes I want to send off for leach tests, as I would
> really like to put them inside platter and bowl forms.
>
> Has anyone on the list already tested their macrocrystalline glazes for
> leaching? Durability? Were you surprised by the results?
>
> Thanks for your help!
>
> --
> Jocelyn McAuley ><<'> jocie@worlddomination.net
> Eugene, Oregon http://www.ceramicism.com
>
>
____________________________________________________________________________
__
> 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.
Edouard Bastarache on sat 11 may 02
Hello Jocelyn.
Ferro frit 3110 49.1%
Zinc Oxide 22.6%
Silica 22.6%
Titanium Dioxide 5.7%
"So far. so good"
I have two versions I am planning on having sent in, one with 5% copper
carbonate, and another with 5% manganese dioxide.
"Copper is not much of a toxicant, unles you suffer from Wilson's disease"
"Manganese is not much absorbed by the gut, gastrointestinal absorption is
generally low (5%). "
Later,
Edouard Bastarache
Irreductible Quebecois
Indomitable Quebeker
Sorel-Tracy
Quebec
edouardb@sorel-tracy.qc.ca
http://sorel-tracy.qc.ca/~edouardb/
http://perso.wanadoo.fr/smart2000/index.htm
Fara Shimbo on sat 11 may 02
Hi, Jocelyn and all,
Re: food safety and crystals, I've done plenty of experiments
with this and here are my observations:
Crystalline glazes are typically soft, it's true, and easily
scratched by cutlery. The addition of 5-10% whiting will
harden them somewhat. The solution to this is to use such
plates for foods that don't involve much cutting or scraping
(chinese food, etc.)
Re: food getting stuck in the crystals: This is certainly
a concern so to check it out I served myself several meals
on crystalline wares, washed them in the dishwasher, and
then used a microscope to look for food particles. Never
found any. This doesn't say you won't, but I never did.
The major sticking point re: food safety and many glazes,
not just crystals, is the crazing. While I've never been able
to develop a crystalline glaze that doesn't craze on a commercial
porcelain or stoneware, I've got two porcelains of my own
invention on which crazing does not occur ... at least not
for the first two months, which is as long as I've had it.
Re: leaching, I've never tried a commercial test, but after
cooking lemon juice and vinegar in a microwave for 15 minutes
(not the same plate) I noticed no difference, even after the
whole sat overnight. This is probably, strickly speaking, not
a valid test but then again, so don't anyone flame me.
Also, I cut a couple of crystalline pieces in half with a
diamond saw, and ran halves through the dishwasher about fifty
times, and left the other halves out. Can't see any difference,
even microscopically.
That's my experience for what it's worth...
Fa
--
++++++++++++++++++++++++++++++++++++++++++++++++++++++++++
Fara Shimbo, Certified Public Nuisance, Master Crystallier
Shimbo Pottery, Hygiene, Colorado, USA
crystalline-ceramics.info ++ shimbopottery.com
++++++++++++++++++++++++++++++++++++++++++++++++++++++++++
"It's great to be known. It's even better to be known
as 'strange.'" -- Kaga Takeshi
Edouard Bastarache on sat 11 may 02
Hello all,
first of all it would be worthy to know if raw materials having
the potential of being really hazardous are used, in the first place.
Later,
Edouard Bastarache
Irreductible Quebecois
Indomitable Quebeker
Sorel-Tracy
Quebec
edouardb@sorel-tracy.qc.ca
http://sorel-tracy.qc.ca/~edouardb/
http://perso.wanadoo.fr/smart2000/index.htm
Jocelyn McAuley on sat 11 may 02
> first of all it would be worthy to know if raw materials having
> the potential of being really hazardous are used, in the first place.
Hello Edouard,
Here is the recipe of the glaze I will have tested:
Ferro frit 3110 49.1%
Zinc Oxide 22.6%
Silica 22.6%
Titanium Dioxide 5.7%
_________________________
I have two versions I am planning on having sent in, one with 5% copper
carbonate, and another with 5% manganese dioxide.
As you can see, this glaze has a large amount of zinc and no clay.
I want to put these glazes on the inside of forms that could be
interpreted as possible food serving containers: bowl shapes and
platters. Even if I give them a stamp on the bottom saying "decorative
use only", I want to test them.
thanks for helping me get information on this.
--
Jocelyn McAuley ><<'> jocie@worlddomination.net
Eugene, Oregon http://www.ceramicism.com
Jeff Lawrence on sat 11 may 02
Hi,
John H. was probably remembering the leach test from Bill Schran's
MFE glaze from a Clay Times article. I added 3% (?) copper and some
rutile. The actual results evanesced when I closed my shop but as I
recall they were well within tolerances for copper.
Jeff
Ababi on sat 11 may 02
The ^6 crystal glazes I used and I believe most of them has 0.04 mol
alumina, to allow running and development of the crystals.
It is hard to believe it can be a stable glaze. I made once a clear
crystal glaze, it was interesting for the test, certainly not for your
costumers
Ababi Sharon
Kibbutz Shoval- Israel
Glaze addict
ababisha@shoval.org.il
http://members4.clubphoto.com/ababi306910/
http://www.milkywayceramics.com/cgallery/asharon.htm
---------- Original Message ----------
>Hi Jocelyn:
>In addition to glaze leaching, there are two other factors to consider
>when
>using a glaze on a food surface: glaze smoothness, and resistance to
>"cutlery" marks.
>Since the surfaces of many zinc-silicate crystalline glazes are not
>perfectly smooth they tend to catch small particles of food and retain
>them
>even through a washing cycle.
>Also these glazes are very frequently "soft." That is, they can be
>rather
>easily marred with an eating utensil.
>If the particular glaze you are using has either of these problems, then
>using it on a food surface is probably not a good idea.
>LeRoy Price
>----- Original Message -----
>From: "Jocelyn McAuley"
>To:
>Sent: Thursday, May 09, 2002 2:12 PM
>Subject: Crystals- food safe?
>> Hello,
>>
>> I have some crystal glazes I want to send off for leach tests, as I
>would
>> really like to put them inside platter and bowl forms.
>>
>> Has anyone on the list already tested their macrocrystalline glazes
>for
>> leaching? Durability? Were you surprised by the results?
>>
>> Thanks for your help!
>>
>> --
>> Jocelyn McAuley ><<'> jocie@worlddomination.net
>> Eugene, Oregon http://www.ceramicism.com
>>
>>
>________________________________________________________________________
>____
>__
>> 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.
>________________________________________________________________________
>______
>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.
Ron Roy on fri 17 may 02
Both will change the taste of food if they are leached out of a glaze -
toxic or not.
It is not our job to provide trace minerals to our customers diets.
RR
>"Copper is not much of a toxicant, unles you suffer from Wilson's disease"
>"Manganese is not much absorbed by the gut, gastrointestinal absorption is
>generally low (5%). "
Ron Roy
RR #4
15084 Little Lake Road
Brighton
Ontario
Canada - K0K 1H0
Phone: 613-475-9544
Fax: 613-475-3513
Ron Roy on fri 17 may 02
Hi Jocelyn,
This not a stable glaze so it will leach whatever is in the glaze into food
- the questions are - is there a toxicity problem - I don't think so, will
the glaze change colour with use - I do think so, will copper and other
"colours" get into food and taint that food - I think so. The change in
taste will not be welcome.
Crystalline glazes like this wind up as two glazes - what is called two
phases - one is the recrystallized -and the other - the glaze in between
the crystals.
As I understand this - the crystals grow - taking silica from the
surrounding glaze - so the crystals tend to be more durable but the glaze
in between tends to be less.
I think better crystalline glazes (more durable) can be made by holding the
glaze at whatever temperature works for growing the crystals - slow cooling
is a better way of say this. That way you can have more silica and alumina
in the glaze and wind up with a more useful product.
Remember - the more they use it the more chance it will get broken and they
will buy another - if they like it enough.
The cry stalline glazes most people use have to be formulated to grow
crystals during a typical fast cooling electric firing. There is a lot of
room for development in this area - the world of slow cooling is just
getting going and we are all in for some spectacular results along the way.
Remember - the more they use it the more chance it will get broken and they
will buy another - if they like it enough.
RR
>> first of all it would be worthy to know if raw materials having
>> the potential of being really hazardous are used, in the first place.
>
>Hello Edouard,
>
>Here is the recipe of the glaze I will have tested:
>
>Ferro frit 3110 49.1%
>Zinc Oxide 22.6%
>Silica 22.6%
>Titanium Dioxide 5.7%
>_________________________
>
>I have two versions I am planning on having sent in, one with 5% copper
>carbonate, and another with 5% manganese dioxide.
>
>As you can see, this glaze has a large amount of zinc and no clay.
>
>I want to put these glazes on the inside of forms that could be
>interpreted as possible food serving containers: bowl shapes and
>platters. Even if I give them a stamp on the bottom saying "decorative
>use only", I want to test them.
>Jocelyn McAuley ><<'> jocie@worlddomination.net
>Eugene, Oregon http://www.ceramicism.com
Ron Roy
RR #4
15084 Little Lake Road
Brighton
Ontario
Canada - K0K 1H0
Phone: 613-475-9544
Fax: 613-475-3513
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