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Hazardous Materials

Hazards in Ceramics

Materials | Allergies | Skin Problems |
Firing Toxins | Basement Kilns |
Fixing a Toxic House
| Dust
Kilns in Schools | Eyesight Damage

Uranium  | Back Injuries | Wrist problems

Disclaimer   This page is in progress and posted by Marvin Bartel. There may be other hazards not included here, so just because something is not listed here, does NOT mean that it is safe to eat, drink, touch, or inhale. If you know of a ceramic hazard not mentioned here, please contact me.

The pottery is probably less hazardous than many workplaces and most potters never suffer serious problems related to their work. However, many materials have not undergone tests for every possible hazard, and illnesses are not always attributed to the correct causes.

I love working with clay and would hate to see anybody be afraid to work with clay. As a teacher I found clay to be wonderful material. Children everywhere for thousands of years have safely enjoyed making things from the clay in their villages. Therefore, if we treat the materials with respect and use common sense, we can get all the fun and benefits without risking our health. I like to take risks in the design and content of artwork, but when working with my materials and methods I make every effort to avoid risk to my health and the health of my customers.    - mb

Lead poisoning from pottery glaze and paint
NO form of lead or arsenic may be used in our materials without specific clearance and training from the instructor. Lead is hazardous to breathe, to ingest (eat), and can be released from firing into the air. Finally, any container glazed with these materials may be toxic to eat or drink from because lead can leach into food or drink stored in the vessel. While new pottery sold today in the United States is generally assumed to be safe from lead, occasionally one still reads about cases of pottery that is accidentally sold with dangerous amounts of lead in the glaze.  Lead has many very serious effects if ingested.  Lead can be absorbed from glazes by acidic food or drink.  Lead is not a colorant, but is used to help the glaze melt, so it can be in low fire glaze of any color.  One should be particularly cautious about old pottery and pottery purchased in countries while traveling.   Inexpensive test kits can now be purchased to test for lead release from paints and pottery glazes. If you need a test kit, do an Internet search for lead check.  

In paint, lead carbonate was formerly used for white.  Lead oxide was a red colorant.  Since white could be part of many tints, lead is very common in old paint.  Lead has contaminated soil around many old houses where it has washed down the siding by rain.  People tracking in dust can poison young children who crawl on the floors.  Children with lead in their systems will have a lower lower intelligence and other serious symptoms.

The following hazardous materials may be used with care and precautions. Workers must NOT inhale the dust or fumes from them and you must NOT ingest (no eating or drinking in the area of use). Never smoke with traces of these materials on your hands. Most of them are not significantly toxic after proper firing in high fired glazes, but make no assumptions without additional research. 

Antimony oxide, barium of any form, beryllium, borax, cadmium, selenium, cobalt, colemanite (or gerstley borate), copper, chromium (chrome), lustre preparations, manganese, nickel, potassium dichromate, vanadium, and zinc. While it may be uncommon, I know a potter who was diagnosed with cobalt and cadmium in his system.  His illness was rare and difficult to diagnose. He became very ill before being correctly diagnosed.  He may have inhaled the toxins in conjunction with smoking while is fingers had toxic residue on them.

The court did not find legal proof of negligence on the part of the chemical suppliers. As clay workers and teachers, we need to take responsibility for our own health and that of our students - at least to the extent we are aware of problems.

FIRING TOXINS

The following materials can liberate toxic fumes while being fired. 

Sulfides, chlorides, fluorides, and to a lesser extent carbonates. This can include many materials such as impure clay, crude feldspars, flourspars, Cornish stone, gypsum, lepidolite, cryrolite, and others.
see Hamer footnote source below.
Monona Rossol has also written extensively on these topics (some are listed at the end of this article).

It is also found that common ball clay contains naturally occurring dioxin and that firing releases the dioxin into the air. Long term breathing of the firing fumes show accumulation in the blood. "Although the number of subjects is small, these results suggest that the dominant route of exposure for case 1 was inhalation of dioxins volatilized during tiring of ceramic pieces in the unvented kilns in the basement of their home."
(2 - Franzblau. et. al.) top of page

AVOID HOME BASEMENT KILN LOCATIONS

Many materials partially volatize (turn to vapor and become airborne) when heated in the kiln. These poisonous gases may include (depending on the materials being fired) antimony, boron, cadmium, dioxin, lead, selenium, zinc, and precious metals. Once airborne you can breath them. Furthermore, they condense on all surfaces they contact. Kilns need to be vented and exhausted to the outdoors.  Most vent systems are not good enough to be totally effective. Therefore, I would not locate a kiln in my home or basement of my home. I would locate kilns in outside shelters or in out buildings that are not inhabited.

Home duct systems and spaces under doors allow basement air to come into the whole house. If you sleep or work in the same building during the firing you will inhale the toxins from the air. It is possible for toxic heavy metal vapors to condense over time on all the walls, floors, and other surfaces of a home that has a kiln repeatedly fired in the basement. Young children invariably rub their hands on these surfaces and become poisoned when they put their fingers in their mouths. Serious health problems can be caused by just living in a house that has had a kiln firing in the basement.

Nobody wants to be knowingly responsible for the retardation of a child's mental development. Locating a kiln in a home basement could damage the brain of a future child whose parents are not aware that there ever was a kiln in this home.

See:Alfred Franzblau, et.al. "Case Report: Human Exposure to Dioxins from Clay" Environ Health Perspect. 2008 February; 116(2): 238–242.
http://www.pubmedcentral.nih.gov/articlerender.fcgi?artid=2235223

This is a report regarding a ceramic hobbyist who had elevated blood serum levels of dioxin. The investigators believe that ball clay was the source of the dioxin. They believe that an unvented kiln in her basement "from the early 1960s to the mid-1990s" was the source of the dioxin in her blood.  She had two friends who had fired kilns in their garages for the same amount of time and had much lower blood serum levels of dioxins.

"Cases 2 and 3 handled ceramic clay in a manner that was similar to that of case 1, but their TEQ and 2,3,7,8-TCDD levels in serum were dramatically lower than hers. The major distinction appears to be that cases 2 and 3 each had only one kiln, which were used less frequently, and the kilns were located in garages, not in the basement or elsewhere inside the living space of their homes."

REMEDIATION FOR A CONTAMINATED HOUSE top of page

If you think a house may be contaminated, test the surfaces for traces of toxins. Many old houses are contaminated because lead was used in paint. Even exterior paint is a problem because it has chalked off and contaminated the earth. This dirt is tracked into the house and children crawl on the floors. Food raised in a garden near the house will contain lead. Fruit trees near the house will produce contaminated fruit.

Get a county or state health department to recommend a testing lab. Remediation may be too complicated for a do-it-yourself approach. If all old paint has to be removed, it requires professional experienced workers who know how to protect their own health. The house probably needs to be vacated during remediation. Check the yellow pages and the Internet for qualified professional companies. Check their work with prior clients and appropriate city and state licensing agencies. In some cases the code may allow covering the old paint with new paint. Check health and building codes. Local housing departments have these regulations.

If the house has surface toxins from a kiln, it should be less difficult to eliminate risk. Redecorate. Get new curtains. Repaint every wall, refinish every floor, put in new carpet, refinish all doors and woodwork before allowing a child to live there and/or before selling the house. I would use chemical tack cloths to prepare surfaces for refinishing. I would avoid sanding old surfaces because it makes dust. I would use wet cleaning methods. I would avoid using a vacuum unless the vacuum unit is outside with only vacuum pipes and hoses inside.

STUDIO ELECTRIC KILNS

If electric kilns in studios are fired regularly in the same air being used by the person or persons working in the studio, there could be an air quality issue. See the section above about kilns in basements, and the possibilities of dioxin in ball clay. (2 - Franzblau. et. al.) Historically, clay was always fired outdoors. What if we placed our electric kilns in uninhabited garden sheds? At least kilns should be in a walled-off separate room with lots of outside ventilation or a fan system that removes firing fumes. I have electric kilns in a separate room. I generally fire it at night when I am not in the same building.

SCHOOL KILNS

School kilns may be too difficult to use if placed in a separate outdoor facility, but it is worth considering for new construction so the logistics can be part of the design of the school. Kilns firing in schools should be tested while firing to be sure fumes do not come into classrooms. Any odor or taste from the kiln that is noticeable in the classroom would be a warning that the vent is not working well enough. The kiln ventilation system should be powerful enough so no air moves from the kiln room to the classroom. Air must be allowed to enter the kiln room so that the vent system can draw out the fumes. The kiln room door can have a permanently open vent or a large space under the door to allow for an air supply. The school ventilation system should not take any air from the kiln room into the school's air system. Vent the kiln fumes outdoors. If you hold a smoking match at the base of the door or at the door vent, you should see the airflow from the classroom into the kiln room. Keep the door closed. Air should not move from the kiln room to the classroom.

I was called to a school that had serious odor in the hallways while the kiln was firing. In this case the roof vent was blocked with snow and the kiln vent was blowing the fumes into the false ceiling area above the kiln and it was polluting the rest of the building. The ductwork leaked because the exit vent was blocked. An exterior exhaust fan would keep negative pressure in the duct system and would be less likely to be blocked by snow, bird nests, etc.

OUCH!
Kilns get very hot. Follow installation instructions carefully to avoid fires. Avoid storage of flammable materials near kilns. Sooner or later most kilns fail to turn off on time and overfire and get very hot. Leave an ample margin of safety when installing.

Head Injuries --- BOING !
Some top loading kilns have a latch to hold the kiln lid open. If this latch fails for any reason, the lid falls shut and could injure the person loading the kiln. I heard from a teacher who received a brain concussion when this happened.

I use a safety chain. It can be attached to a secure anchor bolt in the ceiling or up high on the wall near the back of the kiln. It is a lightweight metal chain with a hook at the bottom end. I place the chain through the lid handle and hook up the chain. Mine is long enough that I can raise the lid just a crack and hang it from the chain. I like this better than a prop for cooling the kiln because it does not damage the kiln brick like a prop does. Of course depending on the handle means that I need to inspect the handle itself to be sure rust has not weakened the handle's attachment bolts, etc.

DUST HAZARDS - top of page Gesundheit

Dust from ordinary clay and several other materials contains some free silica that is too fine and heavy to be expelled from the lungs. Over time this can cause fatal silicosis if breathed often enough. Never carelessly produce dust.

In 2008, I was contacted by an attorney who was representing a woman who had been diagnosed with pneumoconiosis by a board certified pulmonologist. She had chest x-rays and a lung biopsy. It was determined that she had pneumonoconiosis. They believed that clay dust had been the source of her disease. The doctor had taken a complete life history, and the woman had never been exposed to anything else that could cause her lung scarring.

She had inhaled clay dust over 3-4 years in pottery classes she took at a community college. At the end of each semester, she and other students were asked to (and did) sweep the pottery class, and clean pottery cubby holes.  She said that the instructor had not cautioned them about the effects of clay dust.

To avoid raising dust, we should use only wet cleaning methods. Vacuum sweepers, brooms, and brushes do not filter out the fine problematic particles, but simply make them airborne so they are inhaled easier. Never leave scraps of clay or slip where they are walked on. 

Warren MacKenzie has worked with clay all his life.  While every person's experiences are unique, this statement from MacKenzie gives some perspective on the problem of clay dust.

At 81, Warren MacKenzie continues to make pots, despite suffering from lung problems. "When I was young, I was very stupid, and I didn't wear a mask when I mixed clay, and eventually that takes its toll," he says. He lacks the energy to work a full day in the studio. Eventually you wear out," he says. "But I hate to think of it."(3) from NPR (retrieved 3-10-2010)
http://www.npr.org/templates/story/story.php?storyId=4620622

Some talc and other materials contain impurities of asbestos, which can cause cancer if inhaled. Other materials have a structure somewhat similar to asbestos. This is another reason to avoid making dust and breathing the dust.

Dust masks should be used if and when dust cannot be avoided. Dust masks must fit well and they must be specifically designed for very fine dust. Many masks are sold in drug stores that do not qualify. Use only a NIOSH (National Institute for Occupational Safety and Health) approved masks rated for fine toxic dust. They are not effective if they do not fit well.  Persons with a beard cannot depend on the effectiveness of a dust mask. Also see: Monona Rossol. "Respirators & Dust Masks, Part 1."Nov/Dec 1999 issue of Clay Times. Respirators & Dust Masks, Part 2 Jan/Feb 2000 issue of Clay Times. (4)

I use a sealed clay mixer/pugger so that when it is closed, no dust can escape.  It is on wheels. Before I mix clay from dry ingredients, I move it outside. 

Wood ash from a fireplace can be used as glaze. It is very alkaline and can cause skin damage, rash, and so on. Keep hands out of it.  Ball clay contains dioxin. (2)

Radioactive Uranium Oxide
Uranium Oxide was commonly used as a glaze colorant for some colors prior to World War II.  For some years it was not possible for potters to purchase uranium oxide because the government restricted sales.  However, some grades of uranium may again be available from some sources. 
 

One of the most common commercially produced products was dinnerware by Fiesta.  Many collectors still own radio active dishes and some folks still eat off them without knowing they are radioactive.  Most colors of Fiesta brand dishes do not have uranium and are not radioactive.  Click here to see a plate and a piece of X-ray film exposed by it.

The photo here shows the mark on the bottom of a radioactive collector plate.

Knowing what we do today about the its hazards, potters should not use uranium. I heard of a potter whose widow brought suit against a supplier of uranium oxide because she felt her husband's cancer had been caused by uranium.  The widow of the supplier told me about the problem. Her husband had not wanted to acquire the uranium for the potter. He had supplied it only after the potter signed a legal release for the supplier, but this did not keep the potter's widow from bringing suit against the company (then owned by the supplier's widow as the supplier had died of heart problems).

Beware of old supplies lingering around and being passed from potter to potter or from teacher to teacher. I once discovered a brown paper bag with several pounds of earthy yellowish powder in a school supply cabinet in a high school classroom.  When tested with a geiger counter it emitted significant radioactivity.  It was uranium oxide apparently still there from a time prior to World War II when it was commonly sold as a glaze colorant. 

Allergies

A few individuals suffer from special allergies to molds that are normally contained in aging clay. These individuals may find it virtually impossible to work indoors with clay. They may have to restrict their involvement to outdoor work during mild weather. 

Dry Skin - top of page

Almost everybody suffers from dryness of skin after working with clay. Creams and lotions after working are recommended. Also, use these liberally before bedtime if more healing is needed. Rubber gloves are used as a prevention. Cold water is less harmful than hot water when throwing because it does not remove natural oils from the skin as much. 

Back Injuries

One of the most common occupational hazards to potters comes from poor lifting habits related to bags of clay, kiln shelves, and so on. Stand close to the your load. Do not reach over for a heavy item. Place feet on both sides of the heavy item, bend the knees and squat down. Lift by straightening the legs. Lift by bending knees while keeping the back straight. Once injured, a back may never heal properly, but there are therapies to help build back some strength. 

Wrist Injuries

Carpal tunnel syndrome and tendon problems can be caused by overuse or misuse of wrists or/and other joints and muscles. If you begin to feel pain while working you have to rest or change the hand positions. If you feel tingling in the hand or arm during the night change the hand positions or stop the activity that causes swelling or muscle constriction of the nerve. In mild cases you can use a splint from the pharmacy to immobilize the wrist during the night until it heals. If throwing on the wheel or wedging is the offending activity, try changing the way it is done. Use the body more and the wrist less. Take regular breaks. Try some hand building. Limit your use of the computer mouse also. These cause more problems than throwing. 

Vision and Eyesight Concerns

Staring into a white hot kiln to see the cones may damage the eyes.  Intense ultra violet (UV) and infra red (IR) light is emitted. Ordinary eye glasses or sunglasses may protect from some UV, but are not helpful for IR. Welding goggles used by electric arc welders or glasses specifically designed for kiln work are useful to reduce damaging rays. Eye damage is also reduced by staying as far back as possible from the kiln when looking into the kiln. Persons stoking a wood kiln need to take similar precautions to protect their eyes. "Research has shown that UV radiation increases the likelihood of certain cataracts." (5 - U.S. Environmental Portection Agency)


Disclaimer - This page is in progress and posted by Marvin Bartel - There may be other hazards not included here, so just because something is not listed here, does NOT mean that it is safe to eat, drink, touch, or inhale. If you know of a ceramic hazard not mentioned here, please contact me.
        Many materials have not undergone tests for every possible hazard, and illnesses are not always attributed to the correct causes. Therefore, treat all materials with respect. Eating, drinking, smoking while working in a studio can lead to mistakes. Use rubber gloves and protective masks when in doubt. Use common sense. Creative folks enjoy taking risks, but only fools risk the health of themselves or their customers.
_____________________

Also see:
Cleaning the pottery studio or classroom and Working more Safely
Back to Goshen College Art Department Safety Page.

References:

(1) Page 247, Frank and Janet Hamer. The Potter's Dictionary of Materials and Techniques. 1991. A & C Black Limited, London. 

(2) Alfred Franzblau, Elizabeth Hedgeman, Qixuan Chen, Shih-Yuan Lee, Peter Adriaens, Avery Demond, David Garabrant, Brenda Gillespie, Biling Hong, Olivier Jolliet, James Lepkowski, William Luksemburg, Martha Maier, and Yvan Wenger1  "Case Report: Human Exposure to Dioxins from Clay" Environ Health Perspect. 2008 February; 116(2): 238–242. (retrieved 3-10-2010)
http://www.pubmedcentral.nih.gov/articlerender.fcgi?artid=2235223

(3) (from NPR) "Potter Warren MacKenzie's Enduring Craft"

(4) Monona Rossol. "Respirators & Dust Masks, Part 1."Nov/Dec 1999 issue of Clay Times. Respirators & Dust Masks, Part 2 Jan/Feb 2000 issue of Clay Times.

(5) EPA "Health effects of UV overexposure." (retrieved 3-10-2010)
http://www.epa.gov/sunwise/uvandhealth.html#cat

The following articles cover topics in more depth in Clay Times magazine.
http://www.claytimes.com/  Back issues and CDs of multiple editions are available.

Monona Rossol is the author of the following articles.

"Advice for Clay Mixers", 1999 May/Jun:31, 53
"Art Teacher Injured in Pug Mill Accident", 2007 Sep/Oct:55-56
"Barium Glazes: How Safe?", 1995 Nov/Dec:11
"Barium Misconceptions", 1998 Jan/Feb:43
"Building a Safe Pottery Studio", 2000 Nov/Dec:21, 37, 2001 Jan/Feb:37, 42
"Candles, Clay, and Capitalism", 1996 Nov/Dec:31
"Carbon Monoxide Poisoning: A Preventable Illness", 2003 Mar/Apr:52-53
"Ceramic Fiber: Another Option", 1997 Nov/Dec:45
"Ceramic Hazards: Merely Myths?", 2004 Nov/Dec:58-59
"Ceramic Talc: Two Sides of a Story", 2007 Nov/Dec:57-58
"Ceramic Ware Hazards, Past & Present", 1999 Jul/Aug:23, 1999 Sep/Oct:23
"Ceramics & the OSHA Lead Standard", 1998 Nov/Dec:29
"Checking Ventilation Systems: A Do-It-Yourself Procedure", 2008 Jan/Feb:58
"China from China: Ware to Beware of", 2004 May/Jun:46-47
"Chromium: The Green Chemical", 2006 May/Jun:68-69
"Common Sense About Barium Leaching", 1996 Jan/Feb:16
"Dioxin: No Easy Answers", 2001 Jul/Aug:31, 61
"Doc, It Hurts When I Do This!", 1996 Jul/Aug:23
"Ergonomic Injuries: New Regulations", 2001 Mar/Apr:36-37
"Even Very Low Blood Lead Levels Are Harmful", 2003 Sep/Oct:57, 63
"Eyewear for Kiln Gazing", 2000 Jul/Aug:23
"Fashion Footwear for Potters", 2007 Mar/Apr:61-62
"Fertilizer Glazes: Safe or Not?", 1998 Jul/Aug:29
"Filter Facts: How Respirators Work", 2006 Jan/Feb:58-59
"Food-Safe Glazes", 1997 May/Jun:27
"Free EPA Booklet: Environmental Health & Safety in the Arts: A Guide for K-12
Schools, Colleges and Artists", 2007 Jan/Feb:61-63
"From Ceramics to Safety: A Career Odyssey", 2003 Nov/Dec:60-61, 2005
Mar/Apr:9
"HAZCOM Rules Rule", 2003 May/Jun:47, 60
"HazCom Rules Rule, Part II", 2003 Jul/Aug:60-61
"Hospitals, HEPAs, and Health", 2006 Mar/Apr:66-67
"Kids and Clay", 1997 Jul/Aug:27
"A Laboratory for Glaze Testing", 1998 Sep/Oct:29
"Lead: Sources in the Pottery and Home", 2001 Nov/Dec:28-29
"Lead Glazes in Schools", 2006 Nov/Dec:62-63
"Lessons About Clay From *Spin City* and *Planet of the Apes", 2002
Nov/Dec:52-53
"Lessons from a Pug Mill Accident", 2000 Mar/Apr:21
"Libby Vermiculite: An Environmental Disaster", 2004 Jul/Aug:58-59
"Lithium: Metal, Medicine, Menace?", 1998 Mar/Apr:45
"Maintaining a Healthy Studio" (Monona Rossol), 1997 Mar/Apr:27
"Manganese Exposure in the pottery and at the table", 2006 Sep/Oct:68-69
"More on Asbestos in Talc", 2000 Sep/Oct:34, 44
"Museum Photo Policies: A Mental Health Issue", 2004 Jan/Feb:46-47
"New Silica Standard Still in the Works", 2004 Mar/Apr:46-47
"NIOSH Looks at Titanium Dioxide and Studio Safety", 2007 Jul/Aug:53-54
"OSHA Violations: Most Frequently Cited in 2005", 2006 Jul/Aug:68-69
"Other Potters with Illness Come Forward", 2005 Nov/Dec:58-59
"Plaster: Almost Non-toxic", 2004 Sep/Oct:58-59
"Polymer Clays: A Different Kind of Hazard", 2003 Jan/Feb:44-45
"Potters Planning to be Parents (in two parts)", 2002 Jan/Feb:31, 37, 2002
Mar/Apr:31, 42
"Recommendations for High School Ceramics", 2001 Sep/Oct:28, 47
"Respirators & Dust Masks", 1999 Nov/Dec:36
"Respirators & Masks", 2000 Jan/Feb:23
"Safety and Cone 6 Glazes", 2002 Jul/Aug:29, 42
"School Pottery Activities Studied", 1999 Jan/Feb:43
"Shocking New OSHA Rules: Electrical Code Updated", 2007 May/Jun:61-62
"Tales of Vermiculite and Talc", 2000 May/Jun:23
"Testing for Barium Leaching", 1996 Mar/Apr:14
"The Lead Frit Myth", 1998 May/Jun:45
"The True Grit on Grinding", 1996 Sep/Oct:19
"Time to Get the Lead Out", 2001 May/Jun:15, 54
"Too Much Fun Isn't Always Healthy", 1997 Sep/Oct:39
"Unexpected Health Risks for Potters", 1999 Mar/Apr:23, 60
"Uranium: Still Ticking in Some Potteries", 1996 May/Jun:19
"Voluntary Safety Program for Ceramic Fiber", 2002 May/Jun:31, 50
"Warding Off the OSHA Inspector", 2005 Sep/Oct:58-59
"Warren MacKenzie Diagnosed with Silicosis", 2005 Jul/Aug:59-60
"Waste Disposal Rules Alter Ceramic Education", 2005 Jan/Feb:58-59, 2005
Mar/Apr:59-60
"Waste Disposal Rules for Ceramic Schools & Businesses", 2005 May/Jun:55-60
"What are Kiln Emissions?", 2002 Sep/Oct:34, 42
"Winter Skin Care Tips for Potters", 1997 Jan/Feb:27

All rights reserved.  This page Marvin Bartel.  You may link to this page, but you may not post it on your site or publish it.  Scholarly citations are allowed. They require attribution.

This page was updated June28, 2011

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