Silicosis from pottery [compiled: 2006.9.27] (the Dr. Joseph F. Smith Medical library)
and  U.S. Department of Labor defines silicosis

silica is a substance (silicon dioxide) occurring in quartz sand, flint, and agate
. It is used in making glass, scouring and grinding powders, pottery, etc
. Silica is the second most common mineral in the earth's crust
and is a major component of sand, rock, and mineral ores
. Overexposure to dust that contains microscopic, respirable crystalline silica
can cause scar tissue to form in the lungs,
which reduces the lungs' ability to extract oxygen,
and has been associated with other diseases,
such as bronchitis and tuberculosis
. Some studies also indicate an association with lung cancer
[2006.9.27: it's undisputed that cancer is more prevalent in areas of scar tissue,
which silicosis is an abundence of ]
. Typical sand found at the beach does not pose a silicosis threat because
the crystal sizes are are much larger, and do not get deeply embedded
. More than 1 million U.S. workers are exposed to crystalline silica
It is estimated that there are 2 million workers in the United States
employed in occupations at risk for the development of silicosis

. It is the oldest known occupational lung disease, as it can result from tilling soil,
and it is estimated that today there are 2 million US workers
employed in occupations at risk for the development of silicosis
. These include miners, foundry workers, stonecutters, potters and ceramics workers,
sandblasters, tunnel workers, and rock drillers
the industries and activities that pose the greatest potential risk
construction, maufacturing, or extracting
(sandblasting, rock drilling, masonry work, jack hammering, tunneling)
stone cutting (sawing, abrasive blasting, chipping, grinding)
mining (cutting or drilling through sandstone and granite)
foundry work (grinding, moldings, shakeout, core room)              
shipbuilding (abrasive blasting)    

formulation of soaps and detergents ( with abrasives )
ceramics, clay, pottery, and glass manufacturing
(silicates have barbs that cement things together)
(dusty conditions from disturbing the soil,
such as plowing, harvesting,
or setting and laying of railroad track)

Silicosis is a progressive disease that belongs to
a group of lung disorders called pneumoconioses:
. Silicosis is marked by the formation of lumps (nodules) and fibrous scar tissue in the lungs [2006.9.27:
that occur when particles of respirable silica dust get trapped in the the lung`s air sacs (alveoli)
. The characteristic nodules occur  when the immune system`
s hypervigilance begins creating scar tissue to the extent that
the air sac is sealed off, and the immune system continues to attack
minerals that it has no chance of removing ]
. Silicosis is found mostly in adults over 40

How Can Silicosis Be Prevented?

. There is no cure for the disease,
but it is 100 percent preventable if employers, workers, and health professionals
work together to reduce exposures:
     * enforcing controls to minimize workplace exposure to silica dust
such as substitution of substances that are less hazardous than silica

    * Clear identification of dangerous areas in the workplace
and giving them appropriate protective clothing, equipment
[2006.9.27: and federally subsidized engineering controls
in place of less comfortable personal protective devices ]

    * Informing workers about the dangers of overexposure to silica dust,
and training them in safety techniques:
. the Department of Labor staff will distribute free instructional materials
when they inspect mines, construction sites,
and other affected industries.
-- there is also a toll-free telephone information service operated by NIOSH
in the U.S. Department of Health and Human Services
(1-800-35-NIOSH; select option 2, then option 5)
. The package contains a tip sheet of ideas for preventing silicosis,
a guide for working safely with silica,
and stickers for hard hats to remind workers that,
If it's silica, it's not just dust

Causes & symptoms

The precise mechanism that triggers the development of silicosis is
the body`s response to particles of respirable silica dust getting trapped
deep within the lungs, in tiny sacs (alveoli)
[ where the bronchiole meets the cappilary blood vessels ],
and air exchange takes place,
. white blood cells (macrophages) in the alveoli ingest the silica and die
. The resulting inflammation attracts other macrophages to the region
. The [characteristic] nodule is formed
[because] the immune system`s activity has created
so much fibrous [scar] tissue [as to] seal off the alveoli
. The disease process may stop at this point,
or speed up and destroy large areas of the lung
. The fibrosis may continue even after the worker is no longer exposed to silica
[ since the cause is from the immune system`s hypervigilance against
unmovable mineral deposits
and their support of equally unmovable bacterial infections ]

Early symptoms of silicosis include
shortness of breath after exercising and a harsh,
dry cough
. Patients may have more trouble breathing and cough up blood as the disease progresses
. Congestive heart failure can give their nails [and lips] a bluish tint
. Patients with advanced silicosis may have trouble sleeping and experience chest pain, hoarseness,
and loss of appetite [ --on pain of vomitting!]
. Silicosis patients are at high risk for TB, and should be checked for the disease during the doctor's examination.

Patients with silicosis should call their doctor for any of the following symptoms:

    * Tiredness or mental confusion
    * Continued weight loss
    * Coughing up blood
    * Fever, chest pain, breathlessness, or new unexplained symptoms.

Coworkers of anyone diagnosed with silicosis should be examined for symptoms of the disease
. The state health department and the Occupational Safety and Health Administration (OSHA)
or the Mine Safety and Health Administration (MSHA)
must be notified whenever a diagnosis of silicosis is confirmed.

Have Silicosis?

A medical examination that includes a complete work history
and a chest X-ray and lung function test
is the only sure way to determine if a person has silicosis
. Workers who believe they are overexposed to silica dust
should visit a doctor who knows about lung diseases
. The National Institute for Occupational Safety and Health (NIOSH)
recommends that medical examinations occur before job placement or upon entering a trade,
and at least every 3 years thereafter.

Symptom management

There is no cure for silicosis
. Therapy is intended to relieve symptoms, treat complications, and prevent respiratory infections
. It includes careful monitoring for signs of TB
. Respiratory symptoms may be treated with bronchodilators, increased fluid intake,
steam inhalation, and physical therapy
. Patients with severe breathing difficulties may be given oxygen therapy
or placed on a mechanical ventilator
. Acute silicosis may progress to complete respiratory failure:
  Heart-lung transplants are the only hope for some patients.

Patients with silicosis should be advised to quit smoking,
prevent infections by avoiding crowds and persons with colds or similar infections,
and receive vaccinations against influenza and pneumonia
. They should be encouraged to increase their exercise capacity
by keeping up regular activity,
and to learn to pace themselves with their daily routine.

. patients with silicosis should call their doctor for any of the following symptoms:
Tiredness or mental confusion
Continued weight loss
Coughing up blood
Fever, chest pain, breathlessness, or new unexplained symptoms.

  Taking the right precautions in your pottery production facility
can help ensure the long-term health and safety
of you and your employees. 
By Christine L. Grahl 2004

Health and safety is not a popular topic for discussion in the ceramic industry, especially among production potters. As small businesses, potters typically don't have the resources to invest in in-depth research and analysis of potential hazards, or expensive equipment touted as the "solution" to those hazards. Many potters feel that their business simply isn't big enough to worry about such matters-after all, what could be more natural than working with earth's basic elements?

On the one hand, this view is correct. According to Jeff Zamek, a longtime potter, ceramic consultant and author of the book, Safety in the Ceramics Studio, "The statistical information, and behind that the anecdotal information, states that potters as a group do not come down with aluminosis, silicosis or other respiratory diseases as a result of exposure to the materials most commonly used in this industry." However, he notes, the improper use of ceramic materials can be detrimental to potters' health. Additionally, hazards such as working around hot kilns, handling sharp ware, lifting heavy objects and performing repetitive motions often pose problems for potters who do not take the right precautions. There are also environmental and economic considerations-for instance, what happens to excess glaze that is dumped down the drain, and how much glaze is wasted in a given week or month through improper spraying procedures?

To ensure a safe and healthy working (and living) environment, everyone in the industry must explore these and other issues. Armed with the appropriate knowledge and protective equipment, potters will then be free to focus on the most important aspect of their business-making pottery.

Personal Protective Equipment

According to Zamek, a respirator, safety glasses or goggles, and protective gloves are basic pieces of safety equipment that should be found in every pottery studio, no matter how small. "There's not a lot of expense associated with these items-the equipment is low-cost and can be implemented immediately, whether there is just one person in the studio, or five or 10," he says.

Although Zamek believes that ceramic materials themselves are not inherently dangerous, he points out that many airborne particles and vapors can cause respiratory irritation and eventual illness if they are inhaled at high concentrations and/or over long periods of time. The best approach is to control these materials and vapors at the source, before they enter the studio, but this isn't always feasible. To be on the safe side, Zamek advises that potters should wear a respirator whenever mixing clays or glazes, working in or walking through dry material storage areas, cleaning kiln shelves or cleaning the studio.1

Safety glasses and goggles can protect against airborne particles and debris, and infrared varieties can also shield potters' eyes from ultraviolet and infrared radiation when looking into a firing kiln. Rubber or latex gloves can be worn to protect against skin irritants when handling dry or wet raw materials. More important, however, are the heavy-duty, heat-protective gloves used to prevent burns and cuts on potters' hands and arms. "Cuts and burns from reaching into the kiln when it's too hot or when a glaze is razor sharp are some of the most common injuries experienced by potters, yet they can easily be avoided," Zamek says.

Spray Booths

Any studio or production facility that sprays its glazes should also be equipped with spray booths. These devices capture the excess glaze material and prevent them from entering the facility. Many spray booths can also be set up to reclaim the excess glaze and minimize waste.

"It's not enough just to get the excess glaze out of your studio; you have to contain it," says Joe Koons, senior technical advisor for Laguna Clay Co. in City of Industry, Calif., and a longtime ceramic artist and tile maker. "Overspray can easily be 1/4 to 1/2 of the amount of glaze actually sprayed on a piece, which is a tremendous amount of waste. A well designed spray booth is highly efficient, and the amount of glaze it recovers can easily and quickly offset the initial cost of the equipment."

Koons advises that potters look for a system that maximizes glaze recovery while minimizing maintenance and cleaning requirements. "Cleanliness is everything-it is directly related to your profits because it helps you avoid color contamination when working with different colors, and it also aids in glaze recovery. Start with a clean spray booth and clean up when finished, and use a different filter for each color," he says.

Kiln Venting Systems

Kiln venting systems are another way to ensure a healthy indoor environment. "Apart from the sometimes objectionable smell encountered in the first stages of a kiln firing, there can be several potentially harmful emissions released when clay and glaze materials are heated," says Zamek. "Kiln exhaust fumes can release volatile metals and fluorides from clay and glaze raw materials. During the firing, carbon monoxide is also produced and may be generated at higher levels than recommended government Occupational Safety & Health Administration (OSHA) standards."2

Kiln venting systems protect potters against these substances by removing them from the studio. Some systems use an adjustable vent mounted over the top of the kiln, which can be raised and lowered as needed to simplify kiln loading and unloading. Others systems pull fumes out from the bottom of the kiln and allow fresh air to enter from the top of the kiln to ensure even heat distribution. Which design is better?

"A very useful tool in making a decision is to call the kiln vent manufacturer or the ceramics supplier who sells the product and ask for the phone numbers of customers who have purchased a kiln venting system in your area," Zamek says. "Most potters will gladly tell you the good and any deficient points of the venting system they purchased. Ask to visit their studios to see the kiln vent in operation."3

Air Filters/Purifiers

The last several years have seen a significant increase in the number air filtration systems and air purifiers that have come on the market, many of which claim to dramatically reduce the concentration of silica dust and other particulates in a ceramic production facility. But is such a precaution necessary, especially if employees are already wearing respirators during dust-generating operations?

Zamek doesn't think so. "Unfortunately, many people don't know enough about ceramic toxicology, and they easily become scared by reports about certain exposures and hazards that are based on extrapolations of industrial exposures to these materials over long durations in fields such as silica mining. But there is very little data and few health studies available on how potters use ceramic raw materials, or their relative risk," he says. "If potters want to err on the side of caution and invest extra money in an air filtration or purification unit for their studios, they certainly can, but in most cases it's statistically and anecdotally unnecessary."

Doug Van Sickle of Van Sickle Environmental Systems, Sherman Oaks, Calif., who has been a studio potter for nearly 30 years, disagrees. "Exposure to silica dust is cumulative, and a respirator simply can't provide enough protection," he says. "I've seen many people mix glaze in the same room where they handle their other processes, and then take their respirator off after the glaze has been mixed into the water. But the dust is still in the room, so they'll be breathing that in. Dust is also created when you're sweeping the floor, or even just trimming, and many people don't adequately protect themselves during these operations. Using an air purifier can remove silica and particulate matter from the facility, and can significantly reduce the level of risk."

According to Van Sickle, almost all suspended particulate matter in the air has a positive static electric charge and, due to its extremely minute size, remains in the air for five to six hours. A single purifier unit generates billions of negative ions that attract these positively charged particles, regardless of their size. These particles clump together until they have sufficient weight to fall from the air, where they can be sponged or wet-mopped away.

Another air-cleaning option is ambient-air filtration, whereby all of the air in a room circulates through one or more filters that collect the dust particles. According to Dave Bubb, director of representative sales for Trion Inc., Sanford, N.C., the drawback to an ambient-air system is that the dust must first become airborne. "This means that workers can be exposed to the dust before it gets to the air cleaner, and you never get 100% or even near perfect collection, because you're always adding dust to the space. But you can significantly reduce the amount of dust in the air by 60-90% or more with these systems," Bubb says.

An even better option is source control, in which dust collection systems are placed near the process and collect the dust at the source, before it becomes airborne in the facility. However, Bubb notes that such systems can be impractical due to space or operation constraints.

Common Sense

According to Zamek, the most common injuries that affect potters-carpal tunnel syndrome from repetitive activities such as wedging, back pain from improper lifting, and cuts and burns-have less to do with protective equipment than they do with simply using common sense.

"If you're wedging clay or throwing, take frequent breaks. Don't wedge up 50 pieces of clay at a time; wedge up 20 and then do something else and come back to wedging later," he advises. "Alter your work cycle so you're not getting into a situation where you're repetitively doing something for over an hour. If you're lifting kiln shelves, make sure you're lifting them correctly to avoid back injuries. If you're reaching into the kiln, wear protective gloves to avoid cuts or burns."

Zamek also advises that potters request material safety data sheets (MSDSs) on all materials used in their studios, and notes that any company would be wise to compile a "safety booklet" that is required reading for all new employees.

"Avoiding problems is largely a matter of common sense-it's deceptively simple," Zamek says.

Safety  Jeff Zamek` Respirators for Potters

When sweeping the studio, every potter at some point wonders, "What should I do to protect myself from the clay dust?" Imagine what's floating around in your studio when walking or sweeping up at the end of the day. On days when direct sunlight enters the studio, it's possible to see raw materials and clay dust in the air; but it's the stuff you can't see that's the problem.

Clay is a very small hexagonal-plate-shaped particle material and can range from 100 microns (µ) to 0.1µ in size depending on the specific type of clay. (A micron is 1/1000 of an inch.) Potentially, the most hazardous particle sizes are below 10 microns, and potters should try to cut down the inhalation of particles to safe levels. Respirators are very effective at blocking particles, but no respirator is 100% efficient at blocking all particle sizes. Particles in the 0.3-micron range can zigzag through a filter (even though some get trapped) so that a percentage can pass through the respirator, while larger-size particles travel in a straight line and get trapped.

A safe and conservative approach goes a long way in protecting yourself from airborne particles-both visible and invisible. Fortunately, this area of studio safety has been thoroughly researched by industry, and potters can take advantage of the latest array of respirators.

Respirator Filters
Every respirator has some type of filter to trap particles. One of the most effective filters is a HEPA (High Efficiency Particulate Air) filter. They were developed more than thirty years ago by the Hepa Corporation. The name has since become generic and many companies now produce this classification of filters.

For many years, HEPA filters have been the standard for the industry. They have a 99.97% efficiency rating, which means they filter 99.97% of solid particles down to a 0.3-micron size. Some particles at 0.3 microns do not have enough weight to go through the filter, while particles bigger than 0.3 microns have a larger mass, causing them to travel with greater velocity to the filter. HEPA-type filters are recommended whenever heavy metals, such as, chrome, cadmium, vanadium and cobalt are in the work environment.

Respirator Maintenance
The industry standard (though seemingly inexact) for changing filters occurs when any or all of the 3 D's are encountered-Damage to the respirator, Dirty respirators or Difficulty breathing through the respirator. While dirty and damaged respirators are self-explanatory, the difficult breathing requires some explanation. As particles contact the respirator during use and penetrate below the outer surface of the filter, some filter holes are closed, causing a caking effect to occur. This results in the filter becoming more effective in that an increased amount of holes are plugged by the incoming particles. However, at some point the heightened resistance needed to breathe causes unfiltered air to be drawn through the point of least resistance on the mask seal. Before this state is reached, the filter should be discarded.

If It Fits ...
Fit is one of the most important considerations when choosing any respirator, and two factors are essential when placing a respirator on your face. A complete seal around the face is critical in allowing no secondary air to bypass the filter. Make sure the mask conforms to your face so no outside air is drawn in while breathing. Men with beards must ensure that the mask forms an unbroken seal around their face; otherwise, shaving the area is required. The second factor is the comfort of the mask. If the particular mask is uncomfortable or heavy, and it isn't worn on the required occasions, it offers no protection.

Two of the respirators I tested-the Willson Freedom® 2000 Series and Willson Valuair® Plus-come with diagrams and instructions on how to wear the masks, and informative videos were also available. The instructions on use and fit for the 3M 8210, 3M 8110S and 3M 8233 N100 are available from the dealer or by calling the 3M technical service number.

Respirators with higher efficiency (99.97% efficiency) filters can cause greater resistance when breathing due to the use of finer filtering materials. High-efficiency units have an exhalation valve in front to allow for easier breathing.

Willson™ Freedom® 2000 Series Disposable Respirator
Willson™ Freedom® 2000 Series Disposable Respirator
The distinctive feature of this respirator is the simple straightforward design and its light weight on the face. It can be purchased in three face-piece sizes for an exact airtight fit on the face, which is a critical factor in any respirator design. The unit has an excellent P100 filter that is 99.97% effective in trapping particles down to .3 microns in size. This is the highest rating by NIOSH standards. The mask allows for eye wear and feels comfortable when I swept the studio or mixed dry glazes. However, the inability to replace the filter would be a major drawback if the potter was considering it for daily use in the studio. Replacing the entire mask and filter each time would be costly. Retail price $18.55. (Source: Willson Division of WGM Safety Corporation, product information Form No. 9121C.)

Willson™ Valuair® Plus Reusable Respirator
Willson™ Valuair® Plus Reusable Respirator
The easily replaceable filter extends the service life of this unit, which is a major benefit. The filter cartridges are the same ones used in the Willson Freedom 2000 series masks (P100). It also has a soft pliable face piece with adjustable straps to fit almost any face contour. From the first time I used it in my studio, it was very comfortable and there was low breathing resistance upon inhaling. Wearing eyeglasses does not prevent the mask from fitting your face. I would highly recommend the respirator for ceramics supply companies' clay mixing operations. It can also function well in situations where there is heavy-duty prolonged dry raw materials mixing in the studio. Retail price $21.20. (Source: Willson Division of WGM Safety Corporation, product information Form No. 9601.)

3M™ 8210 and 3M 8110S N95 (smaller size)
3M 8210 and 3M 8110S N95 (smaller size)
Commonly referred to as a paper dust mask this is a very lightweight filter that can be custom fit by a thin metal band on the upper part of the mask. The electrostatically charged micromedia fiber attracts and holds airborne particles. Two elastic straps on each side of the mask hold it firmly against the face for an effective seal. I found the mask easy to use and lightweight on my face. The respirator was very comfortable when wearing glasses and as an added benefit had no parts to clean. It is low priced which makes for reasonable replacement costs. Studies have proven this mask to be just as effective as rubber face piece respirators. I would buy a box of the masks and replace them regularly (see Respirator Maintenance). It is rated at 95% filtration efficiency, which means the mask stopped 95% of the particles down to a 0.3 micron size. It can filter cobalt, copper, chrome, iron oxide, silica and manganese. I would recommend the 3M 8210 and 3M 8110S N95 as low-cost effective masks for dry materials encountered in the pottery studio. Retail price @ $.78 cents, box of 20 $15.67. (Source: 3M Product information sheet #3044.)

3M 8233 N100 Particulate Respirator
3M 8233 N100 Particulate Respirator
This is a paper dust mask made from advanced electrostatically charged micromedia fibers. It has fully adjustable straps for a secure soft fit on the face. Also incorporated into the mask is a one-way cool flow valve that makes breathing easier through the finer mesh filter. Its efficiency is 99.97%, making it one of NIOSH's highest-rated filters. OSHA (Occupational Safety and Health Administration) recommends this type of respirator in situations where lead, cadmium, and arsenic are in the workplace. This mask would function well when mixing dry glaze materials that contain cobalt, copper, chrome, iron oxide, silica, and manganese. The higher efficiency rating and high cost per mask is not required for protection against other ceramic raw materials. It could be used in ceramics supply companies' clay mixing operations where exposure and concentration levels would presumably be higher than in a pottery studio. I would use this respirator only if lead, cadmium, or arsenic were present in the studio. Retail price @ $6.03, box of 20, $120.60. (Source: 3M Product information sheet #3094.)

New Standards
In July 1998, the National Institute of Occupational Safety and Health (NIOSH) fully implemented new standards for all respirators (Title 42, Code of Federal Regulations, part 84, referred to as "42 CFR 84"). These new respirator specifications were designed for higher levels of protection against particulate hazards in the workplace. Respirators sold after July 1998 must comply to the new standard and "42 CFR 84" must be conspicuously displayed on the respirator package. In addition to the part 84 particulate requirements, buyers must be aware that respirators are rated and designated for other factors (i.e., N=no oil in environment, R=oil resistant, and P=oil proof). Potters typically need respirators labeled N95 (no oil and 95% efficient) or N100 (no oil and 99.97% efficient), but ratings of R95, R100, P95 or P100 would also be sufficient.

For protection against airborne particles found in the pottery studio, the 3M 8210 and 3M 8110 S N95 respirators were my first choice. All the respirators tested would meet the requirements of potters, but the 3M respirators were lighter in weight, easily replaceable and comfortable. I do not think the 99.97% vs. 95% efficiency respirators would offer a much greater degree of protection for the materials found in pottery studios or commercial clay mixing operations.

When purchasing any respirator, look for the new NIOSH codes. And always carefully read the instructions on maintenance and use of any respirator purchased, as there can be differences between each model and brand.

Most pottery studios and commercial clay mixing operations will require an N95 respirator or an N100 respirator. All the respirators evaluated would meet and exceed the respirator safety requirements of the studio potter. In addition, all units could be used in industrial applications where higher levels and longer exposure rates would be expected as compared with a pottery studio or clay-mixing operation. The higher-efficiency units rated at 99.97% efficiency (Willson Freedom 2000, Willson Valuair Plus and the 3M 8233 N100) would be very effective protection where lead or cadmium are present in the studio. However, the 3M 8210 and 8110S N95 (smaller size) rated at 95% efficiency would also meet studio requirements for safety.

Each respirator was comfortable and adaptable to fit my face, creating an effective seal. The 3M respirators, having only paper-like fibers and elastic straps, were lighter in weight as compared with the Willson respirators.

Respirator cost is not a consideration when health and safety are involved so deciding to purchase the cheapest respirator was not a factor in the evaluation.

NIOSH publishes a pocket guide listing all raw materials and their permissible exposure levels. The 3M company also publishes a similar listing on raw materials, which is updated annually. Potters can use either guide to decide the safe levels of specific raw materials in their studios. If needed, the guides can be used to determine the type and efficiency level of respirator needed in the studio. However, if the potter wanted to pursue air quality to a much greater degree, the first step would be to hire an industrial hygienist who would monitor the studio (estimated cost for the test is $100 to $180) to determine the level of particulate in the air. The information gathered from testing would then indicate the proper respirator type and filter.

Jeff Zamek, a frequent contributor to PMI, works as a ceramics consultant residing in Southampton, Massachusetts. He is the author of What Every Potter Should Know, published by Krause Publications. Contact Jeff at 6 Glendale Woods Dr., Southampton, MA 01073; or by e-mail at

Ceramics at


Clays are minerals composed of hydrated aluminum silicates, often containing large amounts of crystalline silica. Other impurities may include organic matter or sulfur compounds.  Sometimes, grog (ground firebrick), sand, talc, vermiculite, perlite, and small amounts of minerals such as barium carbonate and metal oxides, are added to modify clay properties.  Clays can be worked by hand or on the potter's wheel, or cast in a clay slurry into molds.

Clay is made by mixing dry clay with water in clay mixer.  Clay slip is made by adding talcs which themselves can be contaminated with fibrous asbestos or asbestos-like materials.  Geographical sources of talcs are relevant, for example, New York State talcs are notoriously asbestos-contaminated, while Vermont talcs are not.  Pfizer has some fiber-free talcs.


  1. There have been known cases of silicosis, or "potter's rot, from chronic inhalation of large amounts of free silica during clay mixing.  Symptoms of silicosis include: shortness of breath, dry cough, emphysema, and high susceptibility to lung infections such as tuberculosis.  The disease may take years to develop.  Silica dust exposure is not hazardous by skin contact or ingestion.  
  2. Chronic inhalation of kaolin is moderately hazardous, and can result in kaolinosis, a disease in which the lungs become mechanically clogged. 
  3. Asbestos is extremely toxic by inhalation and possibly by ingestion.  Asbestos inhalation may cause asbestosis, lung cancer, mesothelioma, stomach cancer, and intestinal cancer.
  4. Sand, perlite, grog, and vermiculite contain free silica and are, therefore, highly toxic by inhalation.  Vermiculite is also frequently contaminated with asbestos.
  5. Clay scraps on the floor, bench  and other surfaces can dry and pulverize, producing an inhalation hazard due to the presence of free silica.  Similarly, reconditioning clay by pulverization and sanding finished green ware, can create very high concentrations of hazardous silica dust.


  1. Use premixed clay to avoid exposure to large quantities of clay dust.
  2. Clay storage and mixing should take place in a separate room.  Bags of clay (and other pottery materials) should be stacked on palettes or grids off the floor for easier clean-up.
  3. All clay mixers should be equipped with local exhaust ventilation to remove fine silica dust particles from the air.
  4. Clay mixers should be equipped with proper machine guards so that they cannot be opened to add clay or water while the mixer blades are turning.
  5. Wear separate work clothes while in the studio.  Choose clothes of material and design that don't trap dust.  Wash these clothes weekly, and separately from other laundry.
  6. Avoid contact of clay with broken skin.  Use a skin moisturizer. 
  7. To prevent back problems, always lift with knees bent. Also, use a standup wheel (Cranbrook style treadle wheel), or elevate electric wheels to a height that doesn't require bending over.  Exercise and massage may relieve minor muscular pain.
  8. Keep wrists in unflexed position as much as possible to prevent carpel tunnel syndrome.  Take frequent work breaks. 
  9. Be careful of the moving parts on kickwheels.
  10. Recondition clay by cutting still-wet clay into small pieces, letting them air-dry, and soak in water. 
  11. Finish green ware while still wet or damp with a fine sponge instead of sanding when dry.  Do not sand greenware containing fibrous talc.
  12. Wet mop floors and work surfaces daily to minimize dust levels and prevent dry scraps from becoming pulverized. 


Glazes used to color or finish clay pieces are a mixture of silica, fluxes and colorants.  Common fluxes include lead, barium, lithium, calcium and sodium, and are used to lower the melting point of silica.  The actual colorants, which are an assortment of metal oxides usually account for less than 5% of the glaze by weight.

High fire porcelain and stoneware techniques eliminate the need for lead as a flux.  Also, alkali earth or alkaline earth fluxes can be used for low-fire conditions instead of lead. Silica may also be removed from leadless type glazes.  The substitution can be based on boric oxide as the glass-former, instead of silica.  Alkali earth fluxes include sodium, potassium, and lithium oxides; alkaline earth fluxes include calcium, magnesium, barium, and strontium oxides.  Minerals containing these fluxes include certain feldspars, nepheline syenite, petalite, bone and plant ashes, whiting, and dolomite. 

Glaze components are weighed, sorted and mixed with water.  These materials are often in fine powdered form, and result in high dust exposures.  Glazes can be dipped, brushed, poured, or sprayed on the ceramic piece.

  1. Free silica occur in many of the clays, plant ash, flint, quartz feldspars, talcs, etc. used in glazes.  See the discussion above for the hazards of silica and the disease silicosis.  Weighing and mixing glazes can result in the inhalation of these toxic materials.

  1. If possible, don't use colorants that are known human carcinogens and avoid probable human carcinogens.  There is no known safe level of exposure to carcinogens.
  2. Consider wearing a respiratory when weighing and mixing powdered.  Wet glazes are not an inhalation hazard.  Good housekeeping procedures and cleanup of spills reduce the risk of inhalation or ingestion of toxic dusts.  Wet mop spilled powders.

Kilns (top)

  1. Chlorine, fluorine, sulfur dioxide, nitrogen dioxide, and ozone are highly toxic by inhalation.  Bisque firings of high-sulfur clay have caused the production of great amounts of choking sulfur dioxide.  Other large acute exposures to gases are not common.  Inhalation of large amounts of these gases can result in severe acute or chronic lung problems.  Long-term inhalation of low levels of these gases can cause chronic bronchitis and emphysema.  Fluorine gas can also cause bone and teeth problems.

dust, claydust, masks and respirators

    I had responded directly to Julie Kent's first post about paper
    disposable filters and respirators as I my main work is with an
    environmental consulting company that specializes amongst other things in
    occupation hygiene. Julie's posts are included at the end so you can
    refresh your memory. After she posted again I realized that I was
    assuming a whole lot about respirators and dust masks and decided to get
    some straight information on the whole topic.

    As many people have mentioned, the dust in studios is largely from clay
    and clay contains silicon. Inhaling silicon can cause coughing,
    wheezing, decreased pulmonary function, progressive respiratory symptoms
    and eventually silicosis. It is also an eye irritant and is considered
    carcinogenic. This information is from Niosh Pocket Guide to Chemical
    Hazards available on the web at
    Look up silica, crystalline (as respirable dust). That same source says
    that the time weighted recommended exposure limit is 0.05mg/cubic metre.
    More info on exactly what part of the silica is harmful, the IDHL or
    immediately dangerous to life or health, is also listed.

    The Niosh guide has recommendations for respirator selection. If you are
    to be exposed to 0.5mg/cubic metre (note this is 10 times the maximum
    time weighted exposure limit) you are to use a HIE (APF 10) meaning any
    air-purifying respirator with a high-efficiency particulate filter. APF
    stands for Assigned Protection Factor. APF > (Workplace Airborne
    Concentration / NIOSH Recommend Exposure Limit) If you are exposed to
    1.25 mg/cubic metre of silica dust, you should be wearing a
    PAPRHIE/SA:CF(APF 25) meaning a powered air-purifying respirator with a
    high-efficiency particulate filter operated in a continuous flow mode.

    The 1995 Niosh Respiratory use policy states "It is emphasized that the
    APF in the above criterion is the minimum recommended by NIOSH. The use
    of respirator types with higher APFs is preferred. Specifically, NIOSH
    recommends always selecting the respirator type with the highest APF that
    is compatible with the conditions of each particular workplace. This is
    particularly true for workplace exposures to carcinogens since there may
    be no exposure level below which there is no risk of disease. When
    respirators are used to reduce exposure to carcinogens, the risk of
    disease will decrease as respirators with higher APFs are selected. It is
    further emphasized that the use of respirators in no way eliminates the
    need to reduce ambient workplace exposures to the lowest feasible level
    through the use of process changes and engineering controls."

Lori C. Larsen, P.Ag.
Environmental Project Manager
PHH Environmental Ltd. and a evening and weekend
potter in Vancouver, B.C. Canada

    Great now we know what we need to get a HIE(APF10) so what is that. Well
    an air purifying respirator comes in many forms. It is a device that you
    can draw air through that will filter particles and is usually powered by
    yourself by breathing in (and out). This class includes half face
    respirators, you know the soft rubber ones with two cartridges on either
    side AND includes the disposable throw away paper masks if they are rated
    properly (the ones that everyone has questions about). The new public
    health regulations 42 CFR 84 (in the USA only) state that to protect
    against dusts and mists only you must have an N (not resistant to oil)
    95, 97 or 99.97 percent efficient filter. The old ratings for filters
    used to be Part 11 code filters. Now Niosh also states "Because
    research shows that particles sized 2 micrometers or smaller can
    penetrate some DM [dust & mist respirator (APF=5)]and DFM [dust & mist
    respirator with a full facepiece (APF=10)] filters, these Part 11 filters
    should be used only when the mass median aerodynamic diameter (MMAD) is
    known to be greater than 2 micrometers [NIOSH 1995]. If this diameter is
    less than 2 micrometers or is unknown, a Part 11 HEPA filter or any Part
    84 filter should be used. In Canada, according to my co-workers, only the
    half face respirators with HEPA cartridges are adequate.

    What is the difference between the two?

    Well the rubber half face respirators with high efficiency filters have
    an efficiency rating of 99.97 percent when using filters are commonly
    known as HEPA - High efficiency filters for aerosol. Yes a HEPA filter
    qualifies as a HIE filter. A half face respirator can be fit tested to
    ensure that it is fitting properly and that all the air that you breath
    is going through those filters. This respirator IS more effective than
    the dust masks because it can create a seal on your face BUT it MUST be
    fitted properly.

    The dust masks that Julie mentioned the 3M 8210 N95 meets NIOSH 42 CFR 84
    N95 requirements. You can look at this mask at

    (sorry for the long URL, just click on it) This mask will filter 95
    percent of the dust particulates to 0.3um MMAD (mass median aerodynamic
    diameter) Sodium Chloride Particle challenge. Sounds good right? Not
    exactly. This mask will filter all air that goes through the filter at
    that rate. What about the air that escapes in around the sides??? I
    sort of figured out that the air that escapes in from the sides is just
    one of the reasons why it is rated at 95 percent. My co-worker
    interpreted even differently than what I gleaned from the online NIOSH
    and OSHA articles,. He thought that mask would only have a 95 percent
    efficiency rating if was fitted perfectly and there is NO WAY to test to
    make sure that it fits well. Short of crazy gluing it on to your face
    (which would hurt when you took it off) there is no way to ensure a
    perfect fit. Well you may be able to fit test it using irritant smoke
    but chances are that you won't have access to this.

    So there should be a big "ah ha!" here. Do I see light bulbs going on
    every where? My it IS bright! But I hear you say, NIOSH just say
    particulate filters and don't specify which exactly to use. Well they do
    admit that the minimum for use should be a 95 percent efficient filter
    but readily admit that such filters should be tested to ensure that they
    fit. So in reality, the best respirator is the cartridge ones that you
    can at least do positive and negative air pressure checks yourself and
    can then get an irritant smoke test. (the banana oil test is only for
    filters with organic cartridges!)

    The cost issue is bogus. The dust mask is intended as a one use, being
    one eight hour shift. If you use it less than that, you could probably
    use it a couple of times before throwing it out. You should keep it
    clean and in its original shape. Lets say you are using these masks and
    go through one per week. That $3 times 52 weeks which is $156. For a
    half face respirator you pay an initial $35-$50 for the mask itself then
    the HEPA filters cost you about $7 to $10 a pair and the rule of thumb is
    to replace them every six months sooooo.. lets see here about $70 for a
    half face respirator for a year. MUCH less, MUCH more protection if
    properly fitted and fit tested. Your supplier should be able to get you
    fit tested for the cost of purchasing the filter. If not go elsewhere.

    About that 4 percent comment in the article. I don't know about you, but
    4 % may just mean the difference from feeling healthy and being sick.
    Again your choice.

    Fit testing for half face respirators has been covered adequately in
    dribs and drabs over the last few days. I hope that all this helps you
    make decisions. Now I am going to find that article in Pottery Making
    Industry and email this to the author of it.

And while we're on the subject of dust masks, I was very confused by the
article "Respirators for Potters" in this spring's Pottery Making
Illustrated by Jeff Zamek which listed a paper dust mask as a "first
choice....for protection against airborne particles found in the pottery
studio." Did anyone else stop short at reading that? I was under the
impression that it is very important to have that respirator seal against
your face, otherwise you are breathing in particles around the sides
anyway. The article states that there is a mere difference of 4 percent
(the paper mask filtering 95 percent of particles, and the highest rated
NIOSH particle respirator filtering 99.97 percent)

Now, I have been grumbling on and off about the aforementioned disposable
paper dust masks that are in use at our community art center -- mostly
because it was recommended we re-use them by putting them in a plastic
(!). I refused and toss mine out after one use (cleaning shelves or
grinding ware outside). However, I also refuse to mix glazes inside
they buy me my own particle respirator, because I just feel like those
little flimsy paper things are not enough to stand between me and major
lung problems (as an ex-smoker and an ex-asthma sufferer I try to be
careful). Am I wrong to take this position?

I also shuddered at the opening line in the article where he mentions
sweeping his studio -- who does that? I was under the impression that
studio cleaning should be wet cleaning.

This is becoming a real concern to me especially because of how conscious
am now of the general dust floating around our studio. I make all my
classes wipe down all surfaces and mop all the floors, but not every
teacher does this after each class. Then there's dust lurking in lots of
corners -- uncleaned slab roller cloth and wooden bats, plastic wadded up
in the trash can with dry clay bits all over it, an opened bag of bone
sitting under the wedging table -- the list could go on for days. And
after lab time it is really bad, with people doing the "not me" excuse
messes left everywhere. Short of becoming the janitor and cleaning up
everyone (or leaving my job altogether) what can I do? I've already
my boss (who is not a potter) to order Monona's book, and I keep making
post signs reminding people to clean up, I've posted the the article from
the Laguna website on "the dangers of crystalline silica" but nothing
to help. And I'm leery of pushing too hard. I seem to be the only one
with any concerns and I'm the youngest teacher there....

This is a really difficult issue for me, especially since my
apprenticeships were with really well-trained potters who kept immaculate
studios (I know because I did a lot of the cleaning work!). Is there
anyone else who has had this problem (especially at the community center
level) and dealt with it successfully?

Thanks in advance for any ideas, help or encouragement you could offer.