mel jacobson on sun 7 dec 03
I would like to know how to post the following question on the clayart
discussion:
A couple of months ago I fired a full 1027 electric skutt kiln to ^03 with
majolica work. The majolica recipe contained tin and I used a lot of
chrome for my green decoration. I got a full kiln of fumed pink (ugly
pink) work and had to throw it all out. This week I fired the same
majolica tin based glaze, same kiln, same ^ temp, but NO chrome
decoration. The work all fumed pink again except for the bottoms of the
pots which were not as exposed to the fumes within the kiln. I now think
the chrome from the first firing contaminated my kiln. Is there something
I can do to purge the chrome from my kiln and restore an atmosphere for
clean firing? Also I will change my majolica glaze recipe as well to one
that uses zircopax instead of tin in the hope that any residual chrome
fumes will be rendered ineffective. Thanks, Carolyn Jacobson, 516 487-9421
From:
Minnetonka, Minnesota, U.S.A.
web site: my.pclink.com/~melpots
or try: http://www.pclink.com/melpots
new/ http://www.rid-a-tick.com
Ron Roy on tue 9 dec 03
No doubt about what happened - chrome and tin make pink - and chrome is
volitile - and a carcinogen - and will contaminate a kiln.
I have no idea how long it will take to leave - have a tin glazed tile in
each firing so you can tell when it's gone.
Zirconium silicate (zircopax, opax, super pax) opacified glazes will not go
pink - the white is cooler and whiter than with tin.
RR
>I would like to know how to post the following question on the clayart
>discussion:
>A couple of months ago I fired a full 1027 electric skutt kiln to ^03 with
>majolica work. The majolica recipe contained tin and I used a lot of
>chrome for my green decoration. I got a full kiln of fumed pink (ugly
>pink) work and had to throw it all out. This week I fired the same
>majolica tin based glaze, same kiln, same ^ temp, but NO chrome
>decoration. The work all fumed pink again except for the bottoms of the
>pots which were not as exposed to the fumes within the kiln. I now think
>the chrome from the first firing contaminated my kiln. Is there something
>I can do to purge the chrome from my kiln and restore an atmosphere for
>clean firing? Also I will change my majolica glaze recipe as well to one
>that uses zircopax instead of tin in the hope that any residual chrome
>fumes will be rendered ineffective. Thanks, Carolyn Jacobson, 516 487-9421
Ron Roy
RR#4
15084 Little Lake Road
Brighton, Ontario
Canada
K0K 1H0
Phone: 613-475-9544
Fax: 613-475-3513
Edouard Bastarache Inc. on tue 9 dec 03
Hello all,
"No doubt about what happened - chrome and tin make pink - and chrome is
volitile - and a carcinogen - and will contaminate a kiln.
RR"
Green trivalent chromium used by potters is not carcinogenic.
Plus if you go back to the abstract I send yesterday, you will see
that ventilation keeps the exposure to metals at very low levels
in potters' workshops.
For chromium the personal sampling results varied from 0.089
to 0.306 µg/m3 for an exposure limit in La Belle Province of
0.5 mg/m3 (not µg).
Later,
"Ils sont fous ces quebecois"
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
http://www.digitalfire.com/education/toxicity/
Janet Kaiser on thu 11 dec 03
Hey, Mel! Have you become a cross-dressing potter too??? Is your
Carolyn the equivalent of Claire (Grayson Perry's alter ego)?
Trying to rid yourself of pink is just a rouse... Right?
The image of all 6' 4" of you in a blonde wig and Viking Maiden
outfit had me giggling through my "report" about the Turner
Prize, but I was not going to tell you. Now you prompt me to
anyway... Shan't reveal all the other images of various
Clayarting males though... Especially the guys who already sport
pony tails and handbags... Ha! Ha!...
Love
Janet :o)
*** IN REPLY TO THE FOLLOWING MAIL:
*** From: mel jacobson
*** E-address: melpots@PCLINK.COM
*** Sent: 07/12/2003 Time: 09:49
>I would like to know how to post the following question on the
clayart
>discussion:
>A couple of months ago I fired a full 1027 electric skutt kiln
to ^03 with
>majolica work. The majolica recipe contained tin and I used a
lot of
>chrome for my green decoration. I got a full kiln of fumed pink
(ugly
>pink) work and had to throw it all out. This week I fired the
same
>majolica tin based glaze, same kiln, same ^ temp, but NO chrome
>decoration. The work all fumed pink again except for the
bottoms of the
>pots which were not as exposed to the fumes within the kiln. I
now think
>the chrome from the first firing contaminated my kiln. Is there
something
>I can do to purge the chrome from my kiln and restore an
atmosphere for
>clean firing? Also I will change my majolica glaze recipe as
well to one
>that uses zircopax instead of tin in the hope that any residual
chrome
>fumes will be rendered ineffective. Thanks, Carolyn Jacobson,
516 487-9421
>
>From:
>Minnetonka, Minnesota, U.S.A.
>web site: my.pclink.com/~melpots
>or try: http://www.pclink.com/melpots
>new/ http://www.rid-a-tick.com
>
*** THE MAIL FROM mel jacobson ENDS HERE ***
***********************************************************
The top posted mail was sent by Janet Kaiser
The Chapel of Art : Capel Celfyddyd
8 Marine Crescent : Criccieth : Wales : UK
Centre of Excellence for The Arts
Home of The International Potters' Path
Tel: ++44 (01766) 523570 http://www.the-coa.org.uk
Open: 13.00 to 17.00hrs : Tuesday to Saturday
************** AVG Virus Protected ********************
Ron Roy on thu 11 dec 03
I do think - when we fire chrome - no matter what we start with - it fumes
- and if it fumes we are exposed to it - and it is a carcinogen.
We did a test at Tuckers on trivalent chrome - put some beside a tin glaze
and fired it to cone 04 or cone 6 - can't remember - pretty sure it was
cone 6 - guess what - tin glaze got pink.
Even if the amounts a small - they can still accumulate in our work places.
On top of all that - we have no information about the combination of toxic
materials on our health. Both chrome and manganese fume - so what is the
potential for those in combination.
If we are not going to measure our exposure then it seems to me the next
best strategy is to limit our exposure as much as possible.
I also see a general lowering of limits for toxic materials - Monona cites
a case in point - the lowering of silica levels in the work place in USA -
industry is saying they can't do it - so guess what will happen? Nothing -
and the health of the workers will continue to degrade.
What I am saying here is - industrial limits are limited - to what is
"practical" - in other words achievable in the work place. The burning
question is - if we can do better - should we?
RR
>"No doubt about what happened - chrome and tin make pink - and chrome is
>volitile - and a carcinogen - and will contaminate a kiln.
>RR"
>
>
>
>Green trivalent chromium used by potters is not carcinogenic.
>Plus if you go back to the abstract I send yesterday, you will see
>that ventilation keeps the exposure to metals at very low levels
>in potters' workshops.
>
>For chromium the personal sampling results varied from 0.089
>to 0.306 =B5g/m3 for an exposure limit in La Belle Province of
>0.5 mg/m3 (not =B5g).
>
>
>Later,
>
>
>
>"Ils sont fous ces quebecois"
>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
>http://www.digitalfire.com/education/toxicity/
>
>___________________________________________________________________________=
___
>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
RR#4
15084 Little Lake Road
Brighton, Ontario
Canada
K0K 1H0
Phone: 613-475-9544
=46ax: 613-475-3513=20
Edouard Bastarache Inc. on thu 11 dec 03
Ron,
green chromium oxide used by potters is trivalent = III
and does not carry a "C" designation which stands for carcinogenic.
A-Quebec's exposure limits :
VEMP : Valeur d'Exposition Moyenne Pondérée :
Chromium compound
VEMP
Notes
Chromium (metal)
0.5 mg/m3
Chromium II, compounds,
as Cr.
0.5 mg/m3
Chromium III, compounds,
as Cr.
0.5 mg/m3
Chromium VI, certain water- insoluble compounds,
as Cr.
0.05 mg/m3
C1, RP, EM
Chromium VI, water- soluble compounds,
as Cr.
0.05 mg/m3
C1 = Confirmed carcinogen to humans
RP = Substance whose recirculation is prohibited in accordance with the law
EM = Substance that should be kept at the lowest practicable level
Later,
"Ils sont fous ces quebecois"
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
http://www.digitalfire.com/education/toxicity/
David Hewitt on sat 13 dec 03
In message , Ron Roy writes
>I do think - when we fire chrome - no matter what we start with - it fumes
>- and if it fumes we are exposed to it - and it is a carcinogen.
>
>We did a test at Tuckers on trivalent chrome - put some beside a tin glaze
>and fired it to cone 04 or cone 6 - can't remember - pretty sure it was
>cone 6 - guess what - tin glaze got pink.
>
>Even if the amounts a small - they can still accumulate in our work places.
>
>On top of all that - we have no information about the combination of toxic
>materials on our health. Both chrome and manganese fume - so what is the
>potential for those in combination.
>
>If we are not going to measure our exposure then it seems to me the next
>best strategy is to limit our exposure as much as possible.
At first sight this statement seems very sensible, but pause for a
moment, shouldn't it say 'as much as *is practical*'. If one reduced
ones exposure as much *as possible* one should perhaps not use chrome or
manganese at all. In other contexts perhaps one should not go to town
where the air contaminants are higher. Perhaps one should not use a car.
Certainly smoking and drinking alcohol would be no go areas. Life itself
is a hazard and the only certainty is that it is not going to be
everlasting. One has to be *practical* about it.
>
>I also see a general lowering of limits for toxic materials - Monona cites
>a case in point - the lowering of silica levels in the work place in USA -
>industry is saying they can't do it - so guess what will happen? Nothing -
>and the health of the workers will continue to degrade.
>
>What I am saying here is - industrial limits are limited - to what is
>"practical" - in other words achievable in the work place. The burning
>question is - if we can do better - should we?
Yes, if it is *practical*
When relating these issues to potters, one should not forget that
industrial limits are set on the assumption that someone may be exposed
to a certain condition for a working life, say 40hrs per week for 20
years, or something like that. I am not sure of the exact assumptions
that may be used in different countries.
>
>RR
>
--
David Hewitt
David Hewitt Pottery
South Wales UK
Web:- http://www.dhpot.demon.co.uk
Ron Roy on mon 15 dec 03
As I said - we tested it and the tin glaze turned pink - so it is obvious -
fire it and it becomes a danger.
It is not the only chrome that potters use and all the other forms have a C.
RR
>Ron,
>green chromium oxide used by potters is trivalent = III
>
>and does not carry a "C" designation which stands for carcinogenic.
Ron Roy
RR#4
15084 Little Lake Road
Brighton, Ontario
Canada
K0K 1H0
Phone: 613-475-9544
Fax: 613-475-3513
Ron Roy on mon 15 dec 03
Hi David,
I don't disagree - up to a point.
If I say practical I don't think it is strong enough. Some will simply say
- if I have the window open - and that is enough - it is not. The message I
am trying to convey needs the emphasis considering the cavalier attitude
that prevails among us on the subject of toxic materials.
I just want to be sure everyone understands - there are risks - we all can
decide for ourselves - I am not saying it should not be used - although I
for one will not use it unless I am sure I have minimal exposure.
It is not taught - it is not covered in any of the books we rely on to give
us information about our craft - we are uninformed to say the least.
An interesting bit of information in Mononas latest newsletter - chrome in
cement is going to be banned in Europe because so many workers get
dermatitis from working with it as well as lung problems. I wonder how many
potters are aware that chrome can cause sever skin allergies and slow
healing ulcers of skin and nasal passages.
RR
>In message , Ron Roy writes
>>I do think - when we fire chrome - no matter what we start with - it fumes
>>- and if it fumes we are exposed to it - and it is a carcinogen.
>>
>>We did a test at Tuckers on trivalent chrome - put some beside a tin glaze
>>and fired it to cone 04 or cone 6 - can't remember - pretty sure it was
>>cone 6 - guess what - tin glaze got pink.
>>
>>Even if the amounts a small - they can still accumulate in our work places.
>>
>>On top of all that - we have no information about the combination of toxic
>>materials on our health. Both chrome and manganese fume - so what is the
>>potential for those in combination.
>>
>>If we are not going to measure our exposure then it seems to me the next
>>best strategy is to limit our exposure as much as possible.
>
>At first sight this statement seems very sensible, but pause for a
>moment, shouldn't it say 'as much as *is practical*'. If one reduced
>ones exposure as much *as possible* one should perhaps not use chrome or
>manganese at all. In other contexts perhaps one should not go to town
>where the air contaminants are higher. Perhaps one should not use a car.
>Certainly smoking and drinking alcohol would be no go areas. Life itself
>is a hazard and the only certainty is that it is not going to be
>everlasting. One has to be *practical* about it.
>>
>>I also see a general lowering of limits for toxic materials - Monona cites
>>a case in point - the lowering of silica levels in the work place in USA -
>>industry is saying they can't do it - so guess what will happen? Nothing -
>>and the health of the workers will continue to degrade.
>>
>>What I am saying here is - industrial limits are limited - to what is
>>"practical" - in other words achievable in the work place. The burning
>>question is - if we can do better - should we?
Ron Roy
RR#4
15084 Little Lake Road
Brighton, Ontario
Canada
K0K 1H0
Phone: 613-475-9544
Fax: 613-475-3513
Edouard Bastarache Inc. on mon 15 dec 03
"It is not the only chrome that potters use and all the other forms have a
C.
RR"
Not all the other chromium forms carry a C designation.
Here, only a certain number of insoluble hexavalent chromium
compounds (VI) carry a C designation.
The soluble hexavalent chromium compounds (VI) do not carry a C
designation.
I am sure our specialists who write our regulations in this field are
at least as smart and knowledgeable as those located on the other side
of the Ottawa river or south of the border.
Later,
"Ils sont fous ces quebecois"
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
http://www.digitalfire.com/education/toxicity/
David Hewitt on tue 16 dec 03
Ron,
In message , Ron Roy
writes
>Hi David,
>
>I don't disagree - up to a point.
>
>If I say practical I don't think it is strong enough. Some will simply say
>- if I have the window open - and that is enough - it is not. The message I
>am trying to convey needs the emphasis considering the cavalier attitude
>that prevails among us on the subject of toxic materials.
>
>I just want to be sure everyone understands - there are risks - we all can
>decide for ourselves - I am not saying it should not be used - although I
>for one will not use it unless I am sure I have minimal exposure.
>
>It is not taught - it is not covered in any of the books we rely on to give
>us information about our craft - we are uninformed to say the least.
I don't know what is available in other parts of the world, but the
Health & Safety Executive in the UK provides some very good guidance, a
lot of it in the form of free leaflets. Try www.hse.gov.uk and search on
ceramics, or www.hsebooks.co.uk.
One for example is on 'Control of exposure to silica dust in small
potteries'. This, for example, gives a maximum exposure limit and goes
on to say, 'This limit should not be exceeded and exposures should be
reduced as far below this *as is reasonably practicable*.
Another title is 'Health surveillance' which may be of interest.
We also have 'Ceramic News' issued by the HSE and reports on the
activities of CERIAC, the Ceramics Industry Advisory Committee.
All occupations have some hazards, the important thing, as you say, is
to know what they are and how to handle them. Just because something
can, under some circumstances, cause silicosis or cancer or dermatitis,
etc., does not mean that you should not even look at it or use it. If we
did I think that all industry would shut down. Perhaps, therefore, the
above references will be helpful. If there are other sources of
information on this subject I would welcome knowing of them. I feel sure
that there is a wealth of information available to us somewhere.
David
--
David Hewitt
David Hewitt Pottery
South Wales UK
Web:- http://www.dhpot.demon.co.uk
Ron Roy on sun 21 dec 03
Hello again Edouard,
You missed the point - it's not the toxicity of the material in the bag
that is in question - but we better know which ones we are working with
because some are labeled with the big C.
All chrome fumes during a kiln firing - and it is the fumes that are the
most dangerous - if you don't know that - you should.
RR
>"It is not the only chrome that potters use and all the other forms have a
>C.
>RR"
>
>
>Not all the other chromium forms carry a C designation.
>
>Here, only a certain number of insoluble hexavalent chromium
>compounds (VI) carry a C designation.
>The soluble hexavalent chromium compounds (VI) do not carry a C
>designation.
>
>I am sure our specialists who write our regulations in this field are
>at least as smart and knowledgeable as those located on the other side
>of the Ottawa river or south of the border.
Ron Roy
RR#4
15084 Little Lake Road
Brighton, Ontario
Canada
K0K 1H0
Phone: 613-475-9544
Fax: 613-475-3513
Edouard Bastarache Inc. on sun 21 dec 03
Ron,
A-Firstly, firing will not change the nature of the chrome
used in the glaze. You cannot make hexavalent chromium
from firing trivalent green chromium oxide:
"
Hello all,
as promised a few weeks ago I finally had a meeting with a
metallurgist, about this problem of transforming trivalent chromium to
hexavalent
chromium.
After having given him all the necessary information on pottery making
technology he concluded that it is impossible to produce hexavalent chromium
in our kilns.
Firstly, chromium melts at 1903 C, which is a much higher melting
temperature than
the ones used in pottery making.
Secondly, a very rich oxidizing atmosphere is necessary like the presence of
sodium
peroxide and an oxygen line feeding the kiln as we feed steel furnaces;
I do not think it would be safe for potters to feed their kilns with an
oxygen line.
So, let us forget about this theoritical problem.
Later,
Edouard Bastarache"
B-Secondly, only a few insoluble hexavalent chromium compounds
carry a C designation. Check my last post on this issue:
Carcinogenesis :
Certain hexavalent chromium compounds have been demonstrated to be
carcinogenic on the basis of epidemiologic investigations of workers and of
experimental studies with animals.
In general, these compounds tend to be of low solubility in water and thus,
hexavalent chromium compounds are subdivided into two sub-groups by ACGIH :
a-Water-soluble hexavalent chromium compounds :
1-chromic acid;
2-chromic acid anhydrides;
3-monochromates and dichromates of :
-sodium,
-potassium,
-ammonium,
-lithium,
-cesium,
-rubidium.
b-Water-insoluble hexavalent chromium compounds :
1-zinc chromate,
2-calcium chromate,
3-lead chromate,
4-barium chromate,
5-strontium chromate,
6-sintered chromium trioxide.
C-Thirdly:
"Chromium and ingestion:
"TITLE: Refined exposure assessment for ingestion of tapwater contaminated
with hexavalent chromium: consideration of exogenous and endogenous reducing
agents.
AUTHORS: Kerger BD; Richter RO; Chute SM; Dodge DG; Overman SK; Liang
J;Finley BL; Paustenbach DJAUTHOR AFFILIATION: McLaren/Hart-ChemRisk,
Irvine, CA 92714,
USA.SOURCE: J Expo Anal Environ Epidemiol; VOL 6, ISS 2, 1996, P163-79
SECONDARY SOURCE ID:
TOXBIB/96/384407
ABSTRACT: Laboratory studies were conducted to determine how rapidly and
completely chromium (VI)
[Cr(VI)] is reduced upon contact with common beverages mixed with tapwater.
Studies were performed for
five common beverages (coffee, tea, orange juice, Kool Aid, and powdered
lemonade)spiked with either 10
or 50 mg Cr(VI)/l. The concentrations of Cr(VI) were measured at several
time intervals for up to four hours.
It was demonstrated that each of these beverages had the capacity to reduce
a concentration of > or = 8 mg
Cr(VI)/l within a 15-minute time frame, and that continued monitoring of the
beverages revealed greater
reduction of the Cr(VI). These findings are consistent with the observation
that many foods and beverages,
as well as endogenous body fluids such as saliva and gastric juices, are
capable of reducing substantial
quantities of Cr(VI) to Cr(III). Our exposure assessment shows that the
estimated high-end ingested dose
of Cr(VI) from tap water at both 1 and 5 mg Cr(VI)/l is generally two to
three orders of magnitude below
doses shown to have no adverse health effect in animal studies. When
considered in conjunction with studies
demonstrating that the reductive capacity of gastric juices may exceed 50 mg
Cr(VI) daily,these observations
suggest that little or no Cr(VI) is likely to be absorbed orally at a
reasonable water concentration of Cr(VI),
since tap water is bright yellow at 5 mg Cr(VI)/l."
1-Ingested chromium III (trivalent, an essential nutrient) is nontoxic
and noncarcinogenic to humans and the scientific consensus is
that ingested chromium VI (hexavalent, almost solely a product of
human activity) is poorly absorbed from the gastrointestinal tract.
No evidence of human cancer from oral exposure to chromium was
found in the medical literature.
2-Food is a major source of chromium intake. At least half of the chromium
intake is from food.
3-The major sources of ingested chromium are food and drinking water.
4-There is no evidence that any amount of ingested chromium can cause
cancer.
5-The ingestion of chromium does not make humans more susceptible to
cancers caused by other agents.
Vice versa the exposure to carcinogens does not make humans more
susceptible to develop cancer from chromium.
6-The risk of cancer is not increased by ingestion of chromium.
7-Chromium VI is rapidly converted to chromium III in the stomach as well as
in the blood.Therefore, any body fluid measurements would describe
chromium III levels.This chromium III level would be irrelevant, as chromium
III
is not carcinogenic."
D-Fouthly, in the BC study chromium levels were insignificant,
they varied from 0.089 to 0.306 µgs/m3, not mg/m3 while the
exposure limit in Quebec is 0.5 mg/m3 for trivalent chromium
and 0.05 mg/m3 for hexavalent chromium.
E-Fithly, if you have a chance, take up Toxicology 101 at U. of Toronto.
Later,
"Ils sont fous ces quebecois"
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
http://www.digitalfire.com/education/toxicity/
- Original Message -----
From: "Ron Roy"
To:
Sent: Sunday, December 21, 2003 3:21 PM
Subject: Re: glazes turned pink question
> Hello again Edouard,
>
> You missed the point - it's not the toxicity of the material in the bag
> that is in question - but we better know which ones we are working with
> because some are labeled with the big C.
>
> All chrome fumes during a kiln firing - and it is the fumes that are the
> most dangerous - if you don't know that - you should.
>
> RR
>
> >"It is not the only chrome that potters use and all the other forms have
a
> >C.
> >RR"
> >
> >
> >Not all the other chromium forms carry a C designation.
> >
> >Here, only a certain number of insoluble hexavalent chromium
> >compounds (VI) carry a C designation.
> >The soluble hexavalent chromium compounds (VI) do not carry a C
> >designation.
> >
> >I am sure our specialists who write our regulations in this field are
> >at least as smart and knowledgeable as those located on the other side
> >of the Ottawa river or south of the border.
>
> Ron Roy
> RR#4
> 15084 Little Lake Road
> Brighton, Ontario
> Canada
> K0K 1H0
> Phone: 613-475-9544
> 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.
>
Ron Roy on sun 28 dec 03
Hi Edouard,
I am not theorizing - as I have stated - many times - the experiment was
done - the green chrome oxide we use does fume - as many have experienced.
Either your friend is guessing or we are not talking about the same
material - chrome oxide does fume at the temperatures in our kilns.
I have prepared tiles and will do the test again - anyone who wants to
duplicate the test is welcome - I will post the results when the firing is
done.
Not all toxicologists agree on the dangers of chrome - as Monona states -
some think all should have a C.
The bottom line is - if you use chrome in your glazes breath as little as
possible of the fumes from your kiln. You will also note that many of the
raw materials - such as many clays - have chrome associated with them.
Breathing kiln fumes is a fools game.
RR
>A-Firstly, firing will not change the nature of the chrome
>used in the glaze. You cannot make hexavalent chromium
>from firing trivalent green chromium oxide:
>
>"
>Hello all,
>
>as promised a few weeks ago I finally had a meeting with a
>metallurgist, about this problem of transforming trivalent chromium to
>hexavalent
>chromium.
>After having given him all the necessary information on pottery making
>technology he concluded that it is impossible to produce hexavalent chromiu=
m
>in our kilns.
>Firstly, chromium melts at 1903 C, which is a much higher melting
>temperature than
>the ones used in pottery making.
>Secondly, a very rich oxidizing atmosphere is necessary like the presence o=
f
>sodium
>peroxide and an oxygen line feeding the kiln as we feed steel furnaces;
>I do not think it would be safe for potters to feed their kilns with an
>oxygen line.
>So, let us forget about this theoritical problem.
>
>
>Later,
>
>Edouard Bastarache"
>
>B-Secondly, only a few insoluble hexavalent chromium compounds
>carry a C designation. Check my last post on this issue:
>
>
>Carcinogenesis :
>
>
>
>Certain hexavalent chromium compounds have been demonstrated to be
>carcinogenic on the basis of epidemiologic investigations of workers and of
>experimental studies with animals.
>
>In general, these compounds tend to be of low solubility in water and thus,
>hexavalent chromium compounds are subdivided into two sub-groups by ACGIH :
>
>
>
>a-Water-soluble hexavalent chromium compounds :
>
>1-chromic acid;
>
>2-chromic acid anhydrides;
>
>3-monochromates and dichromates of :
>
> -sodium,
>
> -potassium,
>
> -ammonium,
>
> -lithium,
>
> -cesium,
>
> -rubidium.
>
>b-Water-insoluble hexavalent chromium compounds :
>
> 1-zinc chromate,
>
> 2-calcium chromate,
>
> 3-lead chromate,
>
> 4-barium chromate,
>
> 5-strontium chromate,
>
> 6-sintered chromium trioxide.
>
>
>
>
>C-Thirdly:
>
>"Chromium and ingestion:
>
>"TITLE: Refined exposure assessment for ingestion of tapwater contaminated
>with hexavalent chromium: consideration of exogenous and endogenous reducin=
g
>agents.
>
>AUTHORS: Kerger BD; Richter RO; Chute SM; Dodge DG; Overman SK; Liang
>J;Finley BL; Paustenbach DJAUTHOR AFFILIATION: McLaren/Hart-ChemRisk,
>Irvine, CA 92714,
>
>USA.SOURCE: J Expo Anal Environ Epidemiol; VOL 6, ISS 2, 1996, P163-79
>
>SECONDARY SOURCE ID:
>
>TOXBIB/96/384407
>
>ABSTRACT: Laboratory studies were conducted to determine how rapidly and
>completely chromium (VI)
>
>[Cr(VI)] is reduced upon contact with common beverages mixed with tapwater.
>Studies were performed for
>
>five common beverages (coffee, tea, orange juice, Kool Aid, and powdered
>lemonade)spiked with either 10
>
>or 50 mg Cr(VI)/l. The concentrations of Cr(VI) were measured at several
>time intervals for up to four hours.
>
>It was demonstrated that each of these beverages had the capacity to reduce
>a concentration of > or =3D 8 mg
>
>Cr(VI)/l within a 15-minute time frame, and that continued monitoring of th=
e
>beverages revealed greater
>
>reduction of the Cr(VI). These findings are consistent with the observation
>that many foods and beverages,
>
>as well as endogenous body fluids such as saliva and gastric juices, are
>capable of reducing substantial
>
>quantities of Cr(VI) to Cr(III). Our exposure assessment shows that the
>estimated high-end ingested dose
>
>of Cr(VI) from tap water at both 1 and 5 mg Cr(VI)/l is generally two to
>three orders of magnitude below
>
>doses shown to have no adverse health effect in animal studies. When
>considered in conjunction with studies
>
>demonstrating that the reductive capacity of gastric juices may exceed 50 m=
g
>Cr(VI) daily,these observations
>
>suggest that little or no Cr(VI) is likely to be absorbed orally at a
>reasonable water concentration of Cr(VI),
>
>since tap water is bright yellow at 5 mg Cr(VI)/l."
>
>
>
>
>
>1-Ingested chromium III (trivalent, an essential nutrient) is nontoxic
>
>and noncarcinogenic to humans and the scientific consensus is
>
>that ingested chromium VI (hexavalent, almost solely a product of
>
>human activity) is poorly absorbed from the gastrointestinal tract.
>
>No evidence of human cancer from oral exposure to chromium was
>
>found in the medical literature.
>
>
>
>2-Food is a major source of chromium intake. At least half of the chromium
>
>intake is from food.
>
>
>
>3-The major sources of ingested chromium are food and drinking water.
>
>
>
>4-There is no evidence that any amount of ingested chromium can cause
>
>cancer.
>
>
>
>5-The ingestion of chromium does not make humans more susceptible to
>
>cancers caused by other agents.
>
>
>
>Vice versa the exposure to carcinogens does not make humans more
>
>susceptible to develop cancer from chromium.
>
>
>
>6-The risk of cancer is not increased by ingestion of chromium.
>
>
>
>7-Chromium VI is rapidly converted to chromium III in the stomach as well a=
s
>
>in the blood.Therefore, any body fluid measurements would describe
>
>chromium III levels.This chromium III level would be irrelevant, as chromiu=
m
>III
>
>is not carcinogenic."
>
>
>
>
>
>D-Fouthly, in the BC study chromium levels were insignificant,
>
>they varied from 0.089 to 0.306 =B5gs/m3, not mg/m3 while the
>
>exposure limit in Quebec is 0.5 mg/m3 for trivalent chromium
>
>and 0.05 mg/m3 for hexavalent chromium.
>
>
>
>
>
>E-Fithly, if you have a chance, take up Toxicology 101 at U. of Toronto.
>
>
>
>
>
>Later,
>
>
>
>
>
>
>
>
>
>"Ils sont fous ces quebecois"
>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
>http://www.digitalfire.com/education/toxicity/
>
>
>
>
>
>
>
>
>- Original Message -----
>From: "Ron Roy"
>To:
>Sent: Sunday, December 21, 2003 3:21 PM
>Subject: Re: glazes turned pink question
>
>
>> Hello again Edouard,
>>
>> You missed the point - it's not the toxicity of the material in the bag
>> that is in question - but we better know which ones we are working with
>> because some are labeled with the big C.
>>
>> All chrome fumes during a kiln firing - and it is the fumes that are the
>> most dangerous - if you don't know that - you should.
>>
>> RR
>>
>> >"It is not the only chrome that potters use and all the other forms have
>a
>> >C.
>> >RR"
>> >
>> >
>> >Not all the other chromium forms carry a C designation.
>> >
>> >Here, only a certain number of insoluble hexavalent chromium
>> >compounds (VI) carry a C designation.
>> >The soluble hexavalent chromium compounds (VI) do not carry a C
>> >designation.
>> >
>> >I am sure our specialists who write our regulations in this field are
>> >at least as smart and knowledgeable as those located on the other side
>> >of the Ottawa river or south of the border.
Ron Roy
RR#4
15084 Little Lake Road
Brighton, Ontario
Canada
K0K 1H0
Phone: 613-475-9544
=46ax: 613-475-3513=20
Edouard Bastarache Inc. on sun 28 dec 03
Ron,
I think we are all mixed up:
A-"I am not theorizing - as I have stated - many times - the experiment was
done - the green chrome oxide we use does fume - as many have
experienced.(RR)"
I have never said that green chromium does not fume, I said that in the BC
study the
amounts measured are insignificant because of the presence of ventilation,
even in shops where the best designs of ventilation were not used.
Plus I said that green chromium oxide does not carry a C designation (EB).
B-"Either your friend is guessing or we are not talking about the same
material - chrome oxide does fume at the temperatures in our kilns. (RR)"
My metallugist friend told us you cannot turn trivalent chromium into
hexavalent chromium in pottery making and he explains why (EB).
C-"Not all toxicologists agree on the dangers of chrome - as Monona states -
some think all should have a C.(RR)
Obsolete information, in 1982 I had a steelmill remove a refractory sand
containing
20% trivalent chromium because in those years it was believed, that all
chromium compounds were carcinogenic; today if I had to do the same job I
would
not recommend to get rid of that sand, knowledge changes over time
As a young medical student I learned that aniline was a bladder carcinogen,
it is not anymore; experts reexamined to old data by better research
methodological
means and found out the conclusions of decades ago were not true.
It is a complicated business(EB).
D-"The bottom line is - if you use chrome in your glazes breath as little as
possible of the fumes from your kiln. You will also note that many of the
raw materials - such as many clays - have chrome associated with them.
Breathing kiln fumes is a fools game.(RR)
I agree, as a general rule of thumb, we should never inhaled any type of
fumes
including from smoking "pot". A recent study proved that smoking "pot" 5
times
a day was as noxious to the heart as smoking 20 tobacco cigarettes a day.
I am often times giving hell to a potter friend who has had 4 coronary
by-passes
and still smokes 25 tobacco cigarettes a day + 5 "pot" cigarettes. (EB)
Later,
"Ils sont fous ces quebecois"
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
http://www.digitalfire.com/education/toxicity/
iandol on mon 29 dec 03
In a recent post Edouarde told us that <measured are insignificant because of the presence of ventilation >>
As far as I know the rate of volatilisation will be independent of the =
velocity of air flowing over the material under study but directly =
related to the temperature at which the test or operation takes place =
and the duration for which that temperature is applied.
If Cr2O3 has a melting point over 2300=BA C, are we talking about grams =
per min or micrograms per min at Cone Six? How about some real facts =
being brought into the discussion???
Best regards,
Ivor Lewis. Redhill, South Australia
Ron Roy on fri 9 jan 04
I just unloaded a cone 6 firing with the tin glaze and guess what?
I made a test tile with a small cup at the bottom - put a pinch of green
chrome oxide in the cup after I had glazed the tile with our raspberry
glaze - without the chrome in it. I once fired it to cone 6.
The glaze is all pale pink - front and back even though the cup with the
chrome in it is just at the front.
You can take it to the bank - even though chrome oxide has a very high
melting point - way over cone 10 never mind cone 6 - it fumes.
I have another tile ready - next time I do a bisque I'll pop it in.
Nobody has to believe me - you can easily do the experiment yourself - just
use a chrome tin glaze you know will go pink or red - leave the chrome out
- put some chrome oxide powder close to it and see for yourself.
RR
Ron Roy
RR#4
15084 Little Lake Road
Brighton, Ontario
Canada
K0K 1H0
Phone: 613-475-9544
Fax: 613-475-3513
Pamela Watkins on sat 10 jan 04
Roy,
I 've kept an eye on this old thread because I just revised a frosty black glaze ^6 ox in which I added tin oxide, playing around for something of my own. I was happy with the glaze upon the initial fire.....firing a couple hours after making the glaze. It came out a frosty blue-black with a little crawling (applied
thick) and light pleasing crystalizing. I'd like to eliminate the crawling, but
unsure of alteration chemically. I tried it in the next fire after the glaze sat for a
couple of days and with a lighter coat (anticipated that lighter meant no
crawling). This time I got extensive crawling and pox marks (over mixed
airbubbles) - nothing like the deep blue black of the first fire. Reglazed
w/ hairdryer and that is when I got the sickly pink from the tin.....all the craze
& air pits evened out, but baby blue and pepto-pink was not what I had in
mind.
Also, I fired Randy's Red with the pieces in the initial fire, as well as another of
my glazes and it had no noticable effect of fume contamination on these
glazes, but I'm reluctant to get this glaze going again, as it was a trouble maker!
My thoughts on the pinking of tin: Tin Oxide didn't pinkout until the subsequent fire. Are you indicate green chrome oxide per this post is the reactor, or are all tin glazes pinkos? Are some glazes/chemicals more reactive to the
contamination than other? Thanks for your thoughts and expertise.
And if you have any advice on my BlackJaQ glaze (ps. sprayed on a platter,
it came out a dusty mat grey! I'd like something predictable!) and how to even
it out for reliable results, I'd be happy to email (on or off list) the receipe and
welcome your suggestions.
Peace,
Pamela
~jaq
Ron Roy wrote:
I just unloaded a cone 6 firing with the tin glaze and guess what?
I made a test tile with a small cup at the bottom - put a pinch of green
chrome oxide in the cup after I had glazed the tile with our raspberry
glaze - without the chrome in it. I once fired it to cone 6.
The glaze is all pale pink - front and back even though the cup with the
chrome in it is just at the front.
You can take it to the bank - even though chrome oxide has a very high
melting point - way over cone 10 never mind cone 6 - it fumes.
I have another tile ready - next time I do a bisque I'll pop it in.
Nobody has to believe me - you can easily do the experiment yourself - just
use a chrome tin glaze you know will go pink or red - leave the chrome out
- put some chrome oxide powder close to it and see for yourself.
RR
Ron Roy
RR#4
15084 Little Lake Road
Brighton, Ontario
Canada
K0K 1H0
Phone: 613-475-9544
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/
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JaQart Studio
It is very hard to be simple enough to be good.
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Joyce Lee on sun 11 jan 04
This is being forwarded for Paul Herman.
-------------------------------------------------------------------------=
--------
Hi Ron,
A question comes to mind. Did you put the Chrome on top of glaze?
The reason I ask is this: I've noticed that glazes containing large
amounts of Boron volatilise markedly more than others, regardless of
what colorant you put in them.
So have you proved that Chrome is volatile, or that Boron glazes are
volatile?
Best wishes,
Paul Herman
Great Basin Pottery
423-725 Scott Road
Doyle, California 96109 US
potter@psln.com
----------
>From: Ron Roy
I just unloaded a cone 6 firing with the tin glaze and guess what?
>
> I made a test tile with a small cup at the bottom - put a pinch of =
green
> chrome oxide in the cup after I had glazed the tile with our raspberry
> glaze - without the chrome in it.
John Hesselberth on sun 11 jan 04
On Saturday, January 10, 2004, at 08:22 PM, Pamela Watkins wrote:
> It came out a frosty blue-black with a little crawling (applied
> thick) and light pleasing crystalizing. I'd like to eliminate the
> crawling, but
> unsure of alteration chemically. I tried it in the next fire after
> the glaze sat for a
> couple of days and with a lighter coat (anticipated that lighter meant
> no
> crawling). This time I got extensive crawling and pox marks (over
> mixed
> airbubbles) - nothing like the deep blue black of the first fire.
> Reglazed
> w/ hairdryer and that is when I got the sickly pink from the
> tin.....all the craze
> & air pits evened out, but baby blue and pepto-pink was not what I had
> in
> mind.
>
Hi Pamela,
Ron is signed off for a few days so I'll take a crack at this. The
'standard' cures for crawling (if anything is standard in the world of
clay) include 1) replace 1/2 of any EPK in the recipe with calcined EPK
(adjusting for the zero LOI of the calcined), 2) replacing part of the
EPK with a good ball clay (again adjusting to keep unity numbers the
same), 3) making sure the glaze is thoroughly dry before firing, and 4)
applying more thinly. Also if your glaze recipe has a lot of magnesium
carbonate, that can cause crawling. If you want help in reformulating
against the above send me your recipe off list.
On the pink problem, it comes from the combination of tin oxide and
chromium oxide. It could be from chromium oxide in glaze in the current
firing or an earlier one. The easiest way to get rid of it is to use
zircopax instead of tin oxide--it usually takes about twice as much and
the aesthetics may not be identical.
Lastly, was your glaze thoroughly mixed on your second attempt? It is
always a good idea to rescreen once through an 80 mesh screen in
addition to thoroughly stirring. Rescreening actually does 2
things--it does redisperse any agglomerates, but it also results in
being sure all the thick glop in the bottom of the bucket actually gets
redispersed. Sometimes, if you just stir, there will still be a layer
of sludge in the bottom of the bucket you don't realize is there.
Regards,
John
http://www.frogpondpottery.com
http://www.masteringglazes.com
Paul Herman on sun 11 jan 04
Hi Ron,
A question comes to mind. Did you put the Chrome on top of glaze?
The reason I ask is this: I've noticed that glazes containing large
amounts of Boron volatilise markedly more than others, regardless of
what colorant you put in them.
So have you proved that Chrome is volatile, or that Boron glazes are
volatile?
Best wishes,
Paul Herman
Great Basin Pottery
423-725 Scott Road
Doyle, California 96109 US
potter@psln.com
----------
>From: Ron Roy
> I just unloaded a cone 6 firing with the tin glaze and guess what?
>
> I made a test tile with a small cup at the bottom - put a pinch of green
> chrome oxide in the cup after I had glazed the tile with our raspberry
> glaze - without the chrome in it.
Ron Roy on sun 11 jan 04
Dear Pamela,
Tin without chrome is white - it is used as an opacifier - usually 5% will
do the job.
I'm not surprised the tin gave a frosty look - and it does encourage
recrysallization. Tin is a refractory so it can slow down the melt as well
- especially if your glaze is just melted.
I can help with reformulating to get rid of the crawling but I need the recipe.
Not all tin glazes turn pink - which is why I specified a chrome tin
rink/red glaze for the experiment - I don't know what materials are in the
Randys red but it is true that chrome is a common contaminant in many
materials we use. Keep in mind - it does not take much chrome to make pink
with tin.
I have to sign off ClayArt today as I am going to Florida for a couple of
weeks - email me the recipes when I get back on the 25th - and include all
this so I know what it is about.
RR
>I 've kept an eye on this old thread because I just revised a frosty black
>glaze ^6 ox in which I added tin oxide, playing around for something of my
>own. I was happy with the glaze upon the initial fire.....firing a couple
>hours after making the glaze. It came out a frosty blue-black with a
>little crawling (applied
>thick) and light pleasing crystalizing. I'd like to eliminate the
>crawling, but
>unsure of alteration chemically. I tried it in the next fire after the
>glaze sat for a
>couple of days and with a lighter coat (anticipated that lighter meant no
>crawling). This time I got extensive crawling and pox marks (over mixed
>airbubbles) - nothing like the deep blue black of the first fire. Reglazed
>w/ hairdryer and that is when I got the sickly pink from the tin.....all
>the craze
>& air pits evened out, but baby blue and pepto-pink was not what I had in
>mind.
>
>Also, I fired Randy's Red with the pieces in the initial fire, as well as
>another of
>my glazes and it had no noticable effect of fume contamination on these
>glazes, but I'm reluctant to get this glaze going again, as it was a
>trouble maker!
>
>My thoughts on the pinking of tin: Tin Oxide didn't pinkout until the
>subsequent fire. Are you indicate green chrome oxide per this post is the
>reactor, or are all tin glazes pinkos? Are some glazes/chemicals more
>reactive to the
>contamination than other? Thanks for your thoughts and expertise.
>
>And if you have any advice on my BlackJaQ glaze (ps. sprayed on a platter,
>it came out a dusty mat grey! I'd like something predictable!) and how to even
>it out for reliable results, I'd be happy to email (on or off list) the
>receipe and
>welcome your suggestions.
>
>Peace,
>Pamela
>~jaq
>
>
>
>Ron Roy wrote:
>I just unloaded a cone 6 firing with the tin glaze and guess what?
>
>I made a test tile with a small cup at the bottom - put a pinch of green
>chrome oxide in the cup after I had glazed the tile with our raspberry
>glaze - without the chrome in it. I once fired it to cone 6.
>
>The glaze is all pale pink - front and back even though the cup with the
>chrome in it is just at the front.
>
>You can take it to the bank - even though chrome oxide has a very high
>melting point - way over cone 10 never mind cone 6 - it fumes.
>
>I have another tile ready - next time I do a bisque I'll pop it in.
>
>Nobody has to believe me - you can easily do the experiment yourself - just
>use a chrome tin glaze you know will go pink or red - leave the chrome out
>- put some chrome oxide powder close to it and see for yourself.
>
>RR
>
>Ron Roy
>RR#4
>15084 Little Lake Road
>Brighton, Ontario
>Canada
>K0K 1H0
>Phone: 613-475-9544
>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.
>
>
>
>JaQart Studio
>
>It is very hard to be simple enough to be good.
>
>~Ralph Waldo Emerson
>
>
>
>---------------------------------
>Do you Yahoo!?
>Yahoo! Hotjobs: Enter the "Signing Bonus" Sweepstakes
>
>______________________________________________________________________________
>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
RR#4
15084 Little Lake Road
Brighton, Ontario
Canada
K0K 1H0
Phone: 613-475-9544
Fax: 613-475-3513
Ron Roy on sun 11 jan 04
Hi Paul,
The chrome powder was in the little cup at the base of the tile - it is
still powder after the firing.
The amount of Boron in that glaze is 0.15 in the Seger unity formula -
3.64% - not a high amount.
This will happen with glazes that have no boron by the way.
I am not aware of the fact that Boron is volitile - you say when present in
large amounts - what leads you to believe this? I do know that Sodium is
volitile starting about cone 6.
I am thinking - if there is a volitile oxide in the glaze - how would that
carry the chrome onto the glaze? - seems impossible to me - it would have
to go get the chrome and deposit it back on the glaze.
I am signing off ClayArt today so I will not read your answer till I get
back in two weeks - if you copy your reply to me at my email address I will
be trying to get my email when I am away.
Best wishes - RR
>A question comes to mind. Did you put the Chrome on top of glaze?
>
>The reason I ask is this: I've noticed that glazes containing large
>amounts of Boron volatilise markedly more than others, regardless of
>what colorant you put in them.
>
>So have you proved that Chrome is volatile, or that Boron glazes are
>volatile?
>
>Best wishes,
>
>Paul Herman
Ron Roy
RR#4
15084 Little Lake Road
Brighton, Ontario
Canada
K0K 1H0
Phone: 613-475-9544
Fax: 613-475-3513
| |
|
