Residual Lead In Kilns

[Jennifer Harnetty]

A reader sent this question about residual lead in kilns...

I understand lead, when fired, gives off vapor and what not that effectively settles into a kiln making it unsuitable for use in firing functional ware. Is there any way to test a kiln for this? I have been looking for used kilns but many people are unaware of exactly what might have been fired in them. If lead is in the kiln is there a way to remove the lead, seal it or do something to the kiln as to make it usable again for food ware?

 

Also, do other toxic materials such as Barium and Cadmium result in the same leaching and adhering to a kiln causing it to potentially pass into other ceramics meant for food? Thank you for your time and help!

 

Can anyone weigh in?

[Guest Bill Jones]

I'm not sure what it would take for lead to become vapor in a kiln (its boiling point is 1470 C), but one could use a lead test kit (the same kind that's available for testing paint) to see if a kiln is contaminated with lead. If it is, there is nothing I know of that will mitigate it. My suggestion would be to take the lead test kit along and test the kiln before purchasing.

 

The only way to actually test for whether or not lead would make it into your ware is to fire the kiln with a glaze that contains no lead or cadmium or any other material you don't want. Then have that same ware leach tested by a lab for each material you are concerned about. You would need to make the test vessels to the lab's specifications.

 

 

It is probably best to test the kiln before you buy it with a lead test kit, as Sherman suggested. But you can get rid of lead in a kiln by firing a container of nepheline syenite to absorb it. The container can be made of clay and should be about as big as the inside of the kiln. Put Nepheline Syenite into the container and then fire 270 degrees (F) per hour to 2000 degrees F. Hold for two hours. After firing dispose of the Neph Sy properly. This process doesn't guarantee that all of the lead will be absorbed so you should still have your ware leach tested by a lab!

Here is a list of people who provide these services:

http://www.digitalfire.com/services/consultants/index.php

[Carl]

Just as a follow up question to the suggestion to have your ware leach tested by a lab, does anyone have an idea (in general) about how much it costs to have that done? Was curious to know if it is generally in the $100's, $1,000's or even higher. Thanks!

[earthartam]

Well this is a rather disturbing thread! How many potters out there, professional or hobbyists, have bought their kilns used, never considering that it may have been previously used for god-knows-what purpose with god-knows-what chemicals? I have been using my ancient second-hand kiln for 15 years, and have put countless vessels out into the world, never even imagining there could be a problem with passing on lead poisoning to myself or others! sheesh! Is this really that big a threat to health and safety?? Perhaps all kilns should come with labels explaining the risks that previous users might possibly be causing. Do I need to get shopping for a new kiln, post haste?

[JT JT]

I just tested an old Skutt I picked up at an estate sale. Did four separate lead tests with two different lead test kits I picked up at the hardware store. Three turned up positive for lead one was a maybe on the furniture. Sad to find out it's contaminated but it's a learning experience too.

Two tests on the inside of the kiln on the bare brick were positive, one test on an old glaze drip on a kiln shelf tested positive. These were a very clear pink where the test was done. The final test on kiln stilt seemed to blush on the edges pinkish but was harder to tell. I'm calling it a loss on the whole set up.

Even firing sculpture I may expose the studio to fumes. Google says lead starts to vaporize at 752 F

Pretty low temps actually. 

The tests took a few minutes longer than the directions. So I'd recommend yes test before you buy in multiple spots inside the kiln. Other clues could be things that come with the kiln like glazes. As well as age of kiln. This one they said was not in use within the last 30 years..so 1990ish..I was optimistic but it's probably way older. Model Skutt 175p 

[Mark C.]

I would be curious to test a new brick to see what that shows before you think its left over fumes from 30-40 years ago in the brick. I get the glaze test . I wonder also if that kiln was fired to cone 6 what the test would be after. lead is such a low temp melt (650 F) that  is whats left after a 2000 degree burn.

You got me thinking that all bricks may fail this test for whatever reason?It would be good to test one thats not from that era.

Back in the day when lowfire  was king all clear and many color glazes had lead in them.I would think that those fumes would dissipate with higher temps as vapors and over time all be gone once lead was no longer fired in the kiln .

[Bill Kielb]

2 hours ago, Mark C. said:

Back in the day when lowfire  was king all clear and many color glazes had lead in them.I would think that those fumes would dissipate with higher temps as vapors and over time all be gone once lead was no longer fired in the kiln .

I would be curious also but have seen many studies of lead around kilns. Lead appears very mobile and has influenced the area around commercial kilns to very large radii and has been measured in the plant and wild life at near toxic levels thousands of feet away. Commercial kilns much more substantial, I get it but running your kiln in a basement or small studio? Probably worth the test. Lead begins to volatilize below 800 F degrees I believe and the remediation kilns for specialized site cleanup fire to 2500 degrees or more so probably hard to get rid of completely at cone 6.I remember pictures of old cone 10 production stuff with vessels to catch the lead dripping from the ceiling. Yikes!

[Mark C.]

Bill thats about 100 degrees beyond my cone 11 firing. .

This whole subject needs some testing really. All my electrics only did and do bisquing (no glazing).

The lead raku I did in the 70s was  in a collage  setting and in a long ago fiber kiln here at home which was taken apart in the 70s. Makes me wonder?I'm glad I switched to all my own glazes and high fire in the 70s after collage. When you make your own you are the maker and know whats in it.

Of course leaded frits have been round for a long while. (never used them in cone 10 work). Be interesting to get brick test results from old electrics.

 

[Bill Kielb]

1 hour ago, Mark C. said:

This whole subject needs some testing really. All my electrics only did and do bisquing (no glazing).

The lead pipe we used for service lines was very sturdy! Of course when I was a kid we would break open old mercury switches and play with the mercury. Great fun! I think I only lost ten points in IQ! It’s all right up there with the rolls of asbestos paper we used to protect surfaces from welding sparks. Great stuff, does Not burn! I am surprised I am still alive actually.

[Benzine]

6 hours ago, Bill Kielb said:

Of course when I was a kid we would break open old mercury switches and play with the mercury. Great fun!

I never played with mercury intentionally, but as a kid I accidentally broke a thermometer.  I tried to pick up all the tiny metal BBs that came out of it, but they kept disappearing when I went to grab them...

[liambesaw]

Lead will volatilize at a low temperature, but that doesn't mean it disappears.  Just going hotter doesn't mean the lead will vanish lol.  It will condense on the next coolest thing if it's able, or will remain volatile inside of the bricks and furniture until it is cool enough to condense.

Also the melting point of lead oxide is more like 1650f, not 650f.

The stuff is so dangerous precisely because it's so persistent.  Heavy metals are no joke, they stay around for a long long time and get everywhere.  FWIW I performed a lead test on each of my kilns after I bought them and neither tested positive.

[Arden Katz]

Hi, I had tests done in my kiln with an CRX machine. Tested positive for lead. So extremely low “minuscule.” Lab tested the pieces of the kiln bricks. Low as well. Lab tested 6 bowls and “0 lead & Cadmium.”  With this info. Do you think I’m safe to use my kiln and no longer worry about lead and cadmium? Tired of worrying and losing sleep 

[Arden Katz]

Meant to say  XRX machine! 

[Bill Kielb]

@Arden Katz (XRF) X-ray fluorescent analyzer If that helps.

[Min]

16 hours ago, Arden Katz said:

I had tests done in my kiln with an CRX machine. Tested positive for lead. So extremely low “minuscule.”

I don't know if this is an acceptable method of testing kiln bricks, did you get this verified? What is definition of minuscule? Were there control kiln brick(s) to determine background levels?

16 hours ago, Arden Katz said:

Lab tested 6 bowls and “0 lead & Cadmium.”

Did the lab you sent your samples to use the FDA approved method of testing (using acetic acid that is heated to 35C and held at temp for required amount of time)? 

Containing Pb and Cd isn't the same as releasing Pb and Cd from clay or glass containers.

[Bill Kielb]

On 6/7/2021 at 10:17 AM, Min said:

Did the lab you sent your samples to use the FDA approved method of testing (using acetic acid that is heated to 35C and held at temp for required amount of time)? 

Containing Pb and Cd isn't the same as releasing Pb and Cd from clay or glass containers.

Do you have an recent protocol? Just asking.

[Min]

3 hours ago, Bill Kielb said:

Do you have an recent protocol? Just asking.

Hi Bill,

ASTM C738 - 94(2020) Standard Test Method for Lead and Cadmium Extracted from Glazed Ceramic Surfaces is here, it's behind a $46- paywall.  From a European Commission 2017 report, some testing info is accessible without a paywall. Excerpt from it below where they reference guidelines used by ISO. 

Testing methods for the EU also behind a paywall. (ISO 6486-1:2019)

"European Directive 84/500/EEC stipulates a conventional test using 4 % acetic acid solution as the simulant for ceramics and 24 h at 22 °C as time-temperature exposure. This test is also an ISO standard and a national standard in a large number of countries. In this test, the value of the first migration is taken. Yet, if the limit is based on actual exposure rather than on a conventional migration test, a test that more realistically represents actual use is required. Given that many ceramic materials show a much higher migration during the first use than during subsequent uses, a repeated use test of three subsequent migrations represents better the exposure after the first use of a ceramic material10 . This protocol was therefore investigated to generate results for three successive migration tests in order to represent a repeated use regime. Unless intended for cooking, the worst condition of use of ceramic articles is hot-fill. Under this condition the article is filled with a hot food, and then left to cool down before 9 US FDA/CFSAN - Approximate pH of Foods and Food Products. 10 note: the same approach is also used for plastic materials intended for repeat-use 7 the food is consumed. Generally a testing condition of 2h at 70 °C is considered to represent conservatively this use. However, for practical reasons including safety issues of laboratory operations handling hot acetic acid (corrosive fumes) and difficulties in constant temperature control during migration testing, a condition at room temperature has historically been preferred for ceramic materials. As the duration of a repeat test becomes 3 days, options to potentially accelerate a repeat-use testing were considered for comparisons. An increase of temperature to reduce the time of exposure, while feasible, would cause implementation issues for acetic acid (fumes). Alternative conditions were considered such as the one used by the Council of Europe for metals and alloys with 0.5 % citric acid for 2 h at 70 °C. The introduction of an accelerating pre-conditioning step of higher acidity (10 %, 5 h at 22 °C) was also attempted followed by one single migration with acetic acid 4 % (24 h, 22 °C). Literature suggested that leaving decorated (overglaze) ceramic articles (i.e. overnight or week-end) between repeat tests may cause higher migration of lead. Multiple migrations with a so-called "weekend gap" of 72 h between migration tests were investigated to evaluate its effect on the result of a compliance test. The scope of the study encompassed both daily use ceramic articles as well as several luxury porcelain items of which the expected use could be occasional. In this context, a study was done on the effect of storage on the migration of metals. Articles were tested for migration, stored for different periods from one week to six months, and re-tested to assess the possible evolution of the migration of metals. Methods to test migration specific to the rim were also investigated to compare two standards (ISO/CEN and ASTM) that are commonly used but not required in the current legislation. The aim was to compare the two protocols of the standards. Testing conditions for cookware were investigated. Kinetic studies into tomato sauce were performed in boiling tomato sauce (pH 3.5) up to 6 h and analysing the migration of lead at several time points. Repeated use tests under different conditions in both stimulants and food were compared. The overall experimental plan is summarised in Table 3."

 

 

 

 

 

[Bill Kielb]

@Min
Very cool, Now I feel cheap as I thought it was only $18.00 - $20.00 for me.