ONLINE EXCLUSIVE: Questioning Cobalt

A recent court case is shedding new light on both the myths and realities regarding cobalt and other ceramic raw materials.

Cobalt has traditionally been used as a decorative blue colorant in everything from Chinese porcelain to American salt glazed stoneware. Today, cobalt oxide and cobalt carbonate are still widely used by potters in glaze and slip formulas to develop a light to dark blue color, depending on the amount employed. However, increasingly negative publicity surrounding the health effects of cobalt and other ceramic raw materials is forcing many potters to reevaluate their processes and products.

The problem is not with the specific materials, but with the lack of pertinent health data relating to the effects of these materials on potters. The statistics that are available are based on industrial populations of workers whose exposure and duration rates differ significantly from potters working in craft centers, schools and small studios. Large industries such as mining, paper production and metal manufacturing have the incentive (i.e., avoiding litigation) and money to assemble and document health problems associated with their work environment; as a result, numerous records are available in these areas on raw materials and their effects on worker health. These data have been used as the basis for enacting a number of guidelines and regulations relating to the safe handling of raw materials. However, a central question that has not been addressed is whether an accurate extrapolation of industrial statistics can be applied to potters who have much lower exposure and duration rates.

Many negative attitudes can grow in a climate of ignorance and speculation, and ceramic raw material toxicology has become increasingly subject to exploitation and misunderstanding by the uninformed and misguided. Ignorance of ceramic raw materials by the legal profession, exploitation by individuals who make their income from distorting data, and the revenue potential associated with any form of litigation have all led to an increased amount of conjecture and embellished claims regarding the use of raw materials by potters. A steady flow of articles has been published warning of new ceramic "poisons of the month," and the topic of health factors relating to ceramic materials has attracted alarmist "experts" with access to undiscriminating print media.

The potential for litigation has also increased. Not only can an individual potter be sued, but a ceramic supplier can conceivably be named as party to a lawsuit for selling items to the potter that caused the eventual user real or imagined harm. For example, if a potter sells a coffee cup with a glaze containing cobalt carbonate, and the user claims the glaze transferred harmful amounts of cobalt into his body, both the potter who made the pot and the ceramic supplier who sold the cobalt used in the glaze could be named in the lawsuit. Defending against a lawsuit can be an expensive and time-consuming process, and it is typically devastating to the individuals and small businesses in the pottery production field. Few ceramic supply companies or potters would knowingly sell products that could inflict damage or illness on their customers, but good intentions have little to do with the factors driving litigation. Even if negligence cannot be assigned, the time and money required to defend a lawsuit are considerable. In many instances, legal fees are incurred even if the case does not go to court.

A recent court case concerning cobalt carbonate came about by a confluence of events driven by greed, ignorance and an atmosphere of misguided consumer protection. Ignorance of ceramic raw materials by laymen and "experts," along with the legitimate health concerns of a potter, were brought together with lawyers who did not do their homework. Fortunately, the outcome is shedding new light on both the myths and realities regarding cobalt and other ceramic raw materials.

A cobalt black clay body with a cobalt slip decoration.

Setting the Stage

The potter, a semi-professional with more than 20 years of experience producing high-temperature functional pottery in a garage studio, claimed to have contracted cobalt poisoning. The potter used approximately 5 lbs of cobalt carbonate every four years in various overglaze washes, a glaze and a blue slip. The slip formula contained two tablespoons of cobalt carbonate to one cup of slip and was applied to the greenware by a brush "spattering" method, whereby the cobalt slip was loaded onto the brush and flicked onto the pots. The floor of the pottery studio was exposed to the excess cobalt slip from mixing and application operations.

One of the potter's glazes contained 3% cobalt carbonate and was mixed in 30-gallon containers, which were refilled every three years. The glaze was applied by dipping or pouring it on the bisque pottery. The potter glazed six to eight hours per day, five days per week for a five-month period every year. An overglaze wash containing 60% cobalt carbonate was also brushed over some glazes.

The slips, glazes and overglazes were applied to a clay body that was mixed in the studio. All of the pots were fired in a 30-cubic-foot, sprung-arch downdraft kiln to cone 9 (2300ºF.). The potter had smoked a pipe for 33 years, filling his pipe with tobacco approximately 30 times each day. He also consumed approximately four liters of diet soda per day. He ate, drank and smoked in his studio, which he cleaned periodically with a garden hose.

Evaluating the Symptoms

After noticing symptoms of fatigue, gastrointestinal problems (acid reflux), muscular pain in all major joints, shaking when fatigued, depression, anxiety attacks, headaches, sore mouth, scalp irritation, poor sleep and prolonged infections, he visited his local doctor. After examinations by several physicians, he was placed on a number of medications to relieve the symptoms that had been developing over the last 15 years of working in his pottery studio. On one of his visits to a doctor who had taken a pottery course, it was suggested he might have developed heavy metal poisoning from the cobalt used in his studio. A hair sample from the potter was found to contain cobalt, and he was informed it was also possible that the range of his medical problems fit many of the symptoms associated with cobalt poisoning. The potter was given over 95 chelation treatments, which are used to draw out heavy metals from the system. The potter also began to do a significant amount of research on the Internet, believing his symptoms fit cobalt poisoning.

He then went to the Mayo Clinic in Rochester, Minn., and was evaluated by a number of medical specialists, including internists, neurologists, gastroenterologists, rheumatologists, psychiatrists and a physician specializing in occupational medicine. Their findings did not indicate heavy metal poisoning. Significantly, blood and urine tests were negative for heavy metal poisoning, but a test did indicate an abnormally high level of arsenic in his blood. However, one doctor did tell him "symptomatically" his aliments fit cobalt poisoning, but this opinion was unsupported by the medical facts of the case. (The symptoms for cobalt poisoning are characterized by functional effects on the ventricles and enlargement of the heart [cardiomegaly]. There are no demonstrated musculoskeletal or neurologic effects as a result of exposure to cobalt. Gastrointestinal effects primarily from ingestion include nausea, vomiting and diarrhea.1)

Taking the Case to Trial

Despite the lack of evidence, the potter claimed he contracted cobalt poisoning because the ceramic supply company, which sold the cobalt carbonate, did not list safety instructions and precautions on the packages he purchased before 1998. His purchases of cobalt carbonate after that year did have safety information, but he claimed the labeling did not adequately inform him of the potential hazards when using the material. The petition for damages filed by the potter's lawyers claimed that the cobalt product sold to the plaintiff as designed, constructed, assembled, manufactured, and distributed was defective and unreasonably dangerous when put to a reasonably anticipated use. At some point in the presentation, this claim was extended to include manganese and arsenic poisoning because the initial test of the cobalt carbonate sample contained arsenic and 5.6 parts per million of manganese as trace materials.

The potter alleged he was unable to earn a living and could not work as a result of the ceramic supply company's negligence due to insufficient labeling of their cobalt carbonate product, which also contained manganese and arsenic. He had stopped making pottery because he believed it to be the cause of his health problems. The potter wanted compensation for economic and pecuniary harm, including, but not limited to, past and future medical bills and expenses, and past and future lost wages and income. He further claimed that he had suffered and would continue to suffer pain, emotional and psychological harm and distress, and loss of enjoyment of life. He believed his symptoms were directly related to the cobalt carbonate contained in his slips and glazes. His claim for damages was in excess of $5 million.

Cobalt carbonate.

Defending Cobalt

The ceramic supply company's position was that it is the responsibility of the user to become informed regarding the health and safety procedures needed when working in the field of ceramics. Based on the potter's education and training, he should not have been eating, smoking or drinking in his studio. Most significantly, the defense claimed the potter did not have cobalt, manganese or arsenic poisoning since his extensive medical examination did not indicate such a diagnosis. (The ceramic supply company was not required to prove what illness(es) the potter was suffering from.) Additionally, several physicians and toxicology experts in environmental medicine testified that the potter's history of symptoms did not indicate poisoning from any heavy metal, with one physician speculating that the symptoms could be caused by the array of drugs he was taking for unrelated illnesses.

Evidence presented by the ceramic supply company's lawyers demonstrated that cobalt, manganese and arsenic poisoning are not found in the general population of potters. Previously, this information had been based on anecdotal reports accumulated over 50 years by individual potters and informal surveys taken at the National Council on Education for the Ceramic Arts (NCECA) annual meetings. A statistically accurate study of potters and their use of raw materials was sponsored at the 2000 NCECA meeting through a Potters Health & Safety Questionnaire that was issued to all participants.2 The questionnaire was also listed on the Internet and was available at ceramic supply companies throughout the U.S. The results of the survey indicated that the four most serious health problems potters encounter in their studios are back pain, carpal tunnel syndrome (repetitive motion), cuts (from glaze shards) and burns (from reaching into hot kilns). While a small percentage of potters reported illnesses attributed to raw materials, a search of the National Library of Medicine data banks and other medical libraries did not reveal any diagnosed cases of potters contracting cobalt, manganese or arsenic poisoning.

Cobalt oxide.
During the trial, a spokesperson from Department of Community & Family Medicine, Division of Occupational & Environmental Medicine at the Duke University Medical Center reported that the original cobalt carbonate sample was reanalyzed using a more accurate test, which determined that the sample did not contain arsenic. Furthermore, it was determined that the hair sample taken from the potter, which was initially reported as having high concentrations of cobalt, was within normal limits for the general population.

The most significant finding, of which potters should take note, occurred at Duke University's Medical Center for Occupational & Environmental Medicine. The potter's actual glaze and slip formulas were tested for respirable and ingestible concentrations of cobalt. The exposure assessment was conducted under controlled conditions duplicating the poor ventilation found in the potter's studio. The exposure to cobalt was tested by a modeling technique in which each activity was carried out identically to the actions of the potter in his studio. The glaze and slip formulas were mixed and applied in the same "spatter" technique used by the potter. Respirable exposure and ingestion levels were calculated for an average adult male based on the mixing operations in the potter's studio.

Test results determined-even allowing for a combination of incidental additive ingestion and inhalation in cleaning, mixing, and glazing activities-that daily absorption of cobalt would be in the range of 170-945 micrograms per day. The levels of cobalt the potter was exposed to in his studio were the same as in the general U.S. population on an average day. This was reflected in the testing of hair, blood and urine-values from which fell within the normal range. A risk assessment for cobalt found no adverse effects in humans at exposures of 3400 micrograms per day.3 The assessment of the potter's studio by Duke University's Medical Center for Occupational & Environmental Medicine is believed to be the first documented case of cobalt material toxicity testing in a private ceramic studio.

Aside from the environment, the general population is exposed to cobalt from many occupational and consumer sources. The most significant source of cobalt is found in food and drinking water. Food ingestion alone can average 5-100 microns per day. Drinking water levels can average from 2 to 107 micrograms per liter per day. Background cobalt air levels can range as high as 0.61 micrograms.4 In addition, cobalt is found in vitamin B12. A typical multivitamin contains 4 micrograms of cobalt in the form of B12.5 Cobalt is a necessary element, with background exposures from vitamin preparations, water and food in the range of 30-37 micrograms per day.

Establishing a Verdict

The trial was held in the potter's hometown and lasted six days. After reviewing the testimony of the ceramic supply company's expert witnesses, the potter's expert witnesses and the potter, 12 jurors took less than three hours to reach a verdict in favor of the ceramic supply company.

Measuring the Impact

The court of law is an imprecise instrument for solving ceramic-related toxicology questions. It is simply the wrong tool for determining the health and safety factors associated with the potter's use of ceramic raw materials.

This case represents several related issues concerning the current realities in ceramics. First and foremost are the potter's past and current health, and the debilitating symptoms that he is experiencing. An inaccurate assessment by himself and others has caused a delay in the correct medical treatment of his illness. If nothing else, the medical evidence submitted at trial should eliminate cobalt, manganese or arsenic poisoning as the possible causes for his symptoms. It is hoped that the information presented will direct him to the correct diagnosis and treatment.

The economic impact of the trial on all parties was extensive. Preparation and research for the trial and payment to expert witnesses, in addition to legal and court fees, were substantial. The cost to the ceramic supply company, which is essentially a small business, caused it to revise its selling practices to prevent future litigation. The adjustments will not appreciably increase the safety margins to workers or customers, but will increase the costs to customers. Even though the ceramic supply company defended itself successfully, many companies will eliminate raw materials and services that they feel might cause legal problems. Such preemptive tactics will not serve potters' health interests and will not protect ceramic supply companies from litigation.

The economic balance between safe handling and selling of ceramic materials and reducing legal exposure to lawsuits depends in part on access to expert technical advice, which many ceramic companies cannot afford. Defending against this type of litigation, no matter what the outcome, was a battle that need not have taken place.

A legitimate array of physical symptoms by the potter, which led to a hair sample test for cobalt, caused the potter to seek legal action. When the symptoms did not match cobalt poisoning, manganese and arsenic poisoning were claimed to be the causes of the potter's health issues. While the cobalt carbonate used by the potter did contain 5.6 parts per million of manganese (trace amounts) it did not possess arsenic. Unfortunately, what was most needed at the onset of contemplated legal action was not present-namely, knowledge of ceramic materials and their toxicological effects on potters. Without this understanding, a course of action was taken, giving an economic incentive for the potter and his lawyers to move proceedings along even when the medical facts did not line up with the physical symptoms of the potter. Once the legal mechanism was under way, the costs in time and money for both the defendant and plaintiff started to accrue.

Finding the Truth

No one is arguing for less stringent safety procedures in selling raw materials, or against accurate labeling or potters adhering to appropriate safety measures in their studios. Any means of promoting safety in ceramics should be considered. However, it is important to understand that raw materials used by potters are not inherently dangerous or harmful when used correctly. The best way to protect yourself from any potential illness or injury (and unnecessary lawsuits) is to learn about the materials you are using and their recommended handling procedures.

Material safety data sheets (MSDSs) are one good source for this information. MSDSs contain the material's chemical name, chemical family, hazard class, formula, occupational exposure limits, emergency first aid procedures, waste disposal, respiratory protection requirements, and precautions for handling and storage, which can help you establish safety guidelines for raw material handling procedures within your studio. Make sure to request a MSDS for every raw material you purchase, and then review it carefully before using that material. Additionally, look for seminars and courses in material safety at local colleges and craft centers.

You should also take common sense precautions within your studio, such as wearing a National Institute for Occupational Safety & Health (NIOSH)-approved respirator and/or rubber or latex gloves when working with materials that generate dust.

Raw materials, as used by individual and production potters, have a remarkable safety record. There is no room in the ceramic studio for ignorance or misconceptions about the raw materials we come into contact with on a daily basis. When cobalt was placed on trial, it highlighted several areas of concern for pottery suppliers and producers. Ignorance of the toxicological effects of raw materials caused a false diagnosis, which initiated a rush to litigation. The trial caused an economic loss for the potter and the ceramic supply company without an acceptable solution for either party. A lack of knowledge almost perpetuated an incorrect assessment of cobalt carbonate for the pottery community.

Fortunately, with the right information, we can avoid such unnecessary situations from occurring in the future.

About the Author

Jeff Zamek received bachelor's and master's of fine arts degrees in ceramics from Alfred University, College of Ceramics, Alfred, N.Y. He taught ceramics at Simon's Rock College in Great Barrington, Mass., and Keane College in Elizabeth, N.J. In 1980 he started his own ceramics consulting firm and has contributed articles to Ceramics Monthly, Pottery Making Illustrated, Clay Times, Studio Potter and Craft Horizons, in addition to Pottery Production Practices. His books, What Every Potter Should Know ($31.45) and Safety in the Ceramics Studio ($25.45) are available from Jeff Zamek/Ceramics Consulting Services, 6 Glendale Woods Dr., Southampton, MA 01073. These books can also be ordered online at , through Ceramic Industry's online bookstore. Jeff can be reached at 413-527-7337 or

SIDEBAR: Cobalt Fast Facts

  • Reliable deposits of cobalt are mined in Canada and Southern Africa. The material is extracted as a byproduct of nickel ore mining.
  • Cobalt carbonate (CoC03) and the stronger cobalt oxide (Co02) are metallic coloring agents that have been used by potters throughout the history of pottery making. They can be found as decorative elements in the earliest 12th century salt-glazed ware produced in Germany. Individual artist potters in the U.S. have been using cobalt in both forms for over 50 years.
  • Cobalt will produce stable blues in oxidation and reduction kiln atmospheres at various temperature ranges. It is one of the most potent colorants available and produces a strong blue when added to slips, glazes and overglaze/underglaze washes. One part of cobalt can tint 100,000 parts of a glaze or slip. This widely used metallic coloring oxide can also generate a range of blues and black in clay bodies. Cobalt can also be found in many commercial glazes, stains and underglaze colors.
  • Large-scale industrial uses of cobalt occur in the formulation of steel and chromium alloys.1

1. Hamer, Frank, The Potter's Dictionary of Materials and Techniques, Fourth Ed., A&C Black Publishers Ltd., 1997, pp. 64-65.


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