The materials you use present two hazards you need to think about: Are they poisoning you while working with them? Are they destabilizing your glazes so they dissolve into food and drink?
Are you getting suspicious that lawyers write most of the labels that now appear on material packages? Do all the labels look the same? How does one pick out the materials that are the most dangerous when materials thought to be safe are labeled in the same way as the toxic ones? It seems warnings have lost some of their impact and sometimes seem no better than nothing at all. Each manufacturer publishes
Material Safety Data sheets that outline hazards associated with coming into contact with the material itself, and while these have the same general format, there is a tremendous variety with reference to the information they volunteer, the hazards detail provided, and the degree of harmony between like materials. The average user is overwhelmed by all of these sheets, and reading them tends to make us cynical about how real the warnings are. In addition, these sheets have nothing to do with safety issues surrounding the functional use of glazes made using the materials.
In recent years the subject of material safety and possible safety issues surrounding the functional use of glazed ware with food and drink have become a hot topic on the Internet, in the press, and within educational institutions. There are people putting their heart and soul into trying to educate us about the hazards of many ceramic materials. At the same time there are many, including authors and people of repute, paying absolutely no attention and making glazes from whatever materials and whatever proportions they please. There are some arguing strenuously to defend the use of known poisons and carcinogens because we can't come up with hard data to prove that anyone is being affected by them. There are others campaigning against ceramics in schools and universities, claiming it is just too dangerous.
Surely there is some middle ground we can reach even. I feel the position is best expressed by Monona Rossol, an author, chemist, potter, and activist who summarizes two decades of selfless dedication to this issue on many levels by calling herself an 'industrial hygienist for the arts, crafts, and theatre'. She speaks of the 'ethical' use of materials and formulations. This approach strikes a chord with many who have seen so many cases where the supposed know-it-alls claim total understanding of things and kick down "caution signs" under the banner that no one can produce hard data to justify their existence. Ethical use of materials means we err on the side of safety and the prevailing common sense, and are less swayed by those with hidden agendas and conflicts of interest. If a material like barium, for example, is surrounded in controversy, then glazes that employ it are 'controversial' glazes. Do you suppose anyone would buy your ware if there was a hang-tag on it explaining that industry experts are currently embroiled in heated disputes over the material's safety?
Is the user of your pottery in danger from food or drink dissolving toxic compounds from the glaze surface, from micro-organisms that the glaze surface might provide a home for or from actually swallowing a chip of the glaze that has flaked off the surface? This site has lots of information to help you make your products safe for the end user, it does not require an engineer. There are some really bad glazes out there, we can help you recognize them.
There is some credibility to the statement that silica is the most dangerous material we use since silicosis is the most common ceramic material related health effect in production workers. Silica itself is clearly not a poison, you can eat it with no problems. But quartz crystals can lodge themselves deeply in the air pocket of the lungs so breathing alot of it is obviously not good. But remember, quartz is by far the most abundant mineral in nature. Gravel, concrete, asphat, garden soil, etc are all loaded with quartz. So the minimization of dust is a key component to a safe workplace. Kiln fumes are also obviously potentially hazardous, they need to be vented outside or kilns need to be in a separate room.
There are many articles on material safety on this web site. You can find a list of all of these articles by searching for the word "toxicity" or "safety".As a quick overview following are some general comments. Keep in mind that when I say a material is not generally harmful, I mean in the quantities a person would be exposed to in a clean typical working environment.
Example of a custom made dust collection hood in the material repackaging area of a supplier. The slots along the front suck particles into the duct, the suction comes from an exhaust fan downstream where the pipe exits the building. It has a wall switch and a sliding damper (where the hood enters the pipe) to enable stopping all airflow (to prevent heat loss in the room during cold days). Notice it is located above the scale and heat sealer where most dust is generated during weighing and packaging. Working in front of a system like this enables you to work without breathing any dust at all.
This designation is an international standard for a general purpose respirator to filter out respirable quartz particles (which cause silicosis). Use one of these when working in a area where ventilation is insufficient to remove all of the dust. Use it also in circumstances where there is temporary generation of large quantities of dust. Do not wear this as a substitute for keeping floors and working areas clean.
Out Bound Links
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.
A step-by-step process to put a liner glaze in a mug that meets in a perfect line with the outside glaze at the rim.
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.
Respirable Crystalline Silica (RCS) refers to particles sufficiently small to stay air-born long enough to be inhaled and go deep into the lungs where they become lodged. Extended exposures to lower concentrations or less frequent exposures to higher concentrations can cause silicosis. The World ...
In Bound Links
Toxicology and ceramic materials is a complex subject, what materials and methods pose the greatest dangers, which are the safest?
Many potters do not think about leaching, but times are changing. What is the chemistry of stability? There are simple ways to check for leaching, and fix crazing.
A post to a discussion on the clayart group by Gavin Stairs regarding the food safety of crazed ware.
A wide range of materials are used in ceramics and they present a many hazards. These hazards are often not well understood by engineers and technicians (they focus their efforts on using the material...
Hazards of these materials in ceramic glazes and clay bodies
Glazes are not as inert and stable as many people think. All are slightly soluble and will thus leach to some extent, even if minute, into liquids they come into contact with. However some glazes are dramatically more soluble than others. The subject of leaching and glaze safety can be complex, but ...
By Tony Hansen