A wide range of materials are used in ceramics. Many of them are harmless, they can be breathed or eaten will little effect. Hundreds of tons of clays are sold each year for the specific purpose of eating them! And many more for cosmetic and medicinal uses. Most ceramic materials are inert, insoluble and among the most stable of materials. That means that it is not dangerous to, once in a while, touch or handle the vast majority of materials. However, if there is constant exposure, then long term effects need to be considered. Notwithstanding this, there some materials do have specific acute or short-term exposure hazards (by ingestion or inhalation).
Material hazards are most commonly related to the dust. But there is a need to be sensible about it. One cigarette, for example, does not kill. Nor do 100. But 100,000 can. Likewise, there may be some asbestos fibres in talc or vermiculite, but you will not be harmed by sweeping up a little of either. You will be harmed if exposed to the dust daily for years and take no precautions. Consider frits to illustrate the need for common sense: There are hundreds available. They are ground glass powders, that means each particle is a glass shard, potentially with razor sharp angular edges! It it not easy to find hazards information on frits (likely because there are so many types and each pulverizes to a different particle shape). Yet simple logic tells us to be careful about breathing the dust. And, to illustrate the need for perspective, consider silicosis: It is a much more serious health issue than asbestosis. Yet pretty well all dust in nature contains some quartz. Even gardening, farming or just walking in dry areas expose one to quartz dust. This is because quartz makes up 10% of the planet. So minimizing exposure over the years is the common sense approach.
Some materials produce harmful fumes at certain temperatures during firing. Bodies or glazes with high percentages of manganese dioxide (and other metal oxide raw materials), for example, will fume and should be considered hazardous. The obvious precaution is to install a vent on your kiln.
Some materials are poison or toxic if eaten. Barium carbonate or lithium carbonate are examples. But this is not common.
|Articles||Crazing and Bacteria: Is There a Hazard?
A post to a discussion on the clayart group by Gavin Stairs regarding the food safety of crazed ware.
|Articles||Is Your Fired Ware Safe?
Glazed ware can be a safety hazard to end users because it may leach metals into food and drink, it could harbor bacteria and it could flake of in knife-edged pieces.
|Articles||Attack on Glass: Corrosion Attack Mechanisms
Max Richens outlines the various mechanisms by which acids and bases can dissolve glass and glazes. He provides some information on stabilizing glazes against attack.
|Hazards||Dealing With Dust in Ceramics|
|Hazards||Quartz, Crystalline Silica Toxicity|
International Labour Organization Chemical Safety Database
CDC Toxicity Profiles of many substances
Ceramic glazes can leach heavy metals into food and drink. This subject is not complex, there are many things anyone can do to deal with this issue