Art Safety: Ceramics
Clay is most dangerous when it is in a dry state and the dust can be inhaled. Silica is an ingredient found in a wide variety of materials used by artists and craftspeople, including sand, quartz, foundry molding sand (silica flour), sandstone, calcined diatomaceous earth, granite, flint, many abrasives, slate, clays, fused silica, feldspar and many carving stones. Amorphous or noncrystalline silica includes such materials as diatomaceous earth and cabosil.
Inhalation of large quantities of silica during the mixing of powdered clay is very hazardous and can cause silicosis or "potters rot" after years of exposure. Silicosis takes at least 10 years to develop and entails symptoms such as shortness of breath, dry cough, emphysema, and high susceptibility to lung infections such as tuberculosis. Skin contact and ingestion pose no significant hazards.
Inhalation of large quantities of China clay powder is moderately hazardous, causing kaolinosis, a disease in which the lungs becomes mechanically clogged by the clay. China clay may also cause silicosis if it contains free silica.
Asbestos is highly toxic by inhalation and possibly by ingestion. It may cause asbestosis, lung cancer, mesothelioma, stomach cancer and intestinal cancer. Talcs are often contaminated with asbestos.
Sand, perlite, grog, and vermiculite contain free silica sand are, therefore, highly toxic by inhalation.
Sanding dry clay can create a problem through the inhalation of free silica.
Handling wet clay:
Molds that grow in wet clay may cause respiratory problems similar to pneumonia and asthma-type allergies. Respiratory problems can also result from inhalation of powders that develop when aged clay dries. The molds, which can contribute to the workability of the clay, can cause skin problems, particularly if there is a pre-existing dermatitis.
Handling cold wet clay, such as when throwing clay, can cause abrasion and drying of the hands, particularly the fingertips. This is a result of the mechanical friction or rubbing of the clay particles on the hands, the oil absorbing ability of the clay, and the harmful effects from prolonged exposure to cold water.
Mechanical/Physical Safety Hazards:
The use of a kickwheel for throwing clay is a mechanical hazard since the moving parts can cause cuts and abrasions, particularly with children.
Small pieces of wet clay that collect on the floor and bench can dry and becomes pulverized, producing an inhalation hazard due to the presence of free silica. This also applies to the process of reconditioning clay or grog.
Glazes also pose health and safety concerns, due to the presence of toxic heavy metals, such as cobalt, hexavalent chromium, nickel, titanium and vanadium. These powdered glazes are respiratory hazards, in addition to being carcinogenic and teratogenic.
- Control exposures to crystalline silica by substituting premixed glazes for those that require mixing of dry powders; if premixed glazes are not feasible, intall properly designed local exhaust ventilation to capture airborne contaminants at the point of generation.
- Install an effective local exhaust ventilation at the wedging table to reduce potential for exposure to silica, and use wet methods to clean the table or use a vacuum cleaner equipped with a HEPA filter.
- Clean floors, table and other surfaces thoroughly and regularly to reduce potential exposure to crystalline silicia -- using wet methods and or a HEPA vacuum cleaner will help prevent dust from becoming airborne.
- Launder student aprons frequently to remove dry clay, a likely source of airbone silica.
- Implement an effective chemical hazard communication program to ensure that teachers and students are aware of the hazards of materials they are using.
- Crystalline Silica Primer, US Department of the Interior, US Bureau of Mines, Branch of Industrial Minerals, (1992)
- A Guide to Working Safety with Silica, U.S. Department of Labor, National Institute of Occupational Safety and Health
- Health Effects of Occupational Exposure to Respirable Crystalline Silica, NIOSH Hazard Review, April 2002
- Silica and Silicosis, OSHA Silica Advisor