Lead glazes used in ceramic ware can be a health hazard, affecting the intellectual development of young children. Poisoning can occur if the lead leaches into your food or drink.
Use of lead glazes
Lead glazes are most commonly used on earthenware, and on older bone china and porcelain. They are reliable, easy to control, durable for most purposes and they produce attractive glazes.
When the glazes are properly formulated and fired at a high temperature, the lead is sealed. However, if they are not properly prepared and fired, lead may leach (i.e. move from the glaze) into food stored in or on the ceramic ware.
The degree of lead leaching from tableware can vary. It depends on how often the tableware is warmed and used, and the amount of contact it has with food and drink. Cups and bowls are of greater concern than dishes. Acidic foods will accelerate any leaching.
These days, raw or free lead is rarely used. The lead is compounded with silicate into a frit, which is less dangerous. In catalog use, manufacturers label the glazes containing lead and use terms such as lead-free, non-toxic and dinnerware-safe to identify lead-free glazes.
However, it is worth checking your kitchen to identify risky items and to ensure their use does not create health hazards.
Risky ceramic ware Ceramic ware with a corroded glaze is extremely dangerous and it should never be used to serve food or drink. It is easy to see corroded glaze because it has a chalky-grey residue that is present after the item has been washed.
Old tableware, especially imported items, homemade or handcrafted china should be treated cautiously. Testing is recommended.
Highly decorated ceramic ware is of concern because of the high lead levels that are typically found in brightly colored glazes. Be wary of highly colored glazes on inside surfaces that could have contact with food or drink, as the potter might not have anticipated that the item would be used in this way when applying the glaze.
Decorations on top of the glaze may present a health hazard. The decoration is on top of the glaze if you can feel it when you rub your fingers across the ceramic ware or if you can see the brush strokes of the decoration above the glazed surfaces.
What to do to reduce the risks Ceramic ware and glazes that are risky should not be used to store food or drink. The longer the food is in contact with such glazes, the more the lead will leach into it.
Highly acidic foods (for example citrus juices, apple or tomato juice, cola, salad dressings, vinegar, coffee, tea and tomatoes) should not be served in questionable china.
Questionable china should not be used daily. Be wary of old coffee mugs, cheap, imported china and ceramic containers. Heating or microwaving questionable china should be avoided. Heat can accelerate the lead-leaching process. Reheating coffee in an old mug in the microwave is a particularly risky thing to do.
Testing for lead Small test kits available from some paint wholesalers and hardware stores can test ceramic ware for lead. The instructions are on the packet. The only drawback is that overseas experience with many of these test kits suggests that false negative and false positive results may occur.
As an alternative, a samples can be sent to a laboratory for analysis.
If you have any doubts about your ceramic ware, don’t use it.
The Dangers of Lead in Pottery - For Potters and Ceramic Artists
Handling glazes containing lead, even occasionally, can be harmful to human health if dust or fumes containing lead are swallowed or breathed in. When lead glazes are used, strict precautions are advised when mixing, applying or firing them. Where possible, it is better to avoid using glazes that contain lead.
Glazes containing lead Lead is found in pottery glazes as lead bisilicate in frits. These glazes are mainly used on earthen and raku ware. If they are not properly formulated, applied and fired it is possible that they could leach into food or drink.
Leadless glazes and low-solubility, lead-bisilicate glazes made with frits give lead-release figures well within international standards and they are readily available from most major suppliers. Lead borosilicate frits give a higher lead-release figure and so should be avoided.
Keep yourself and your family safe
It is important to avoid exposure to lead dust and fumes. You should:
1.keep young children and pregnant women out of the work area and away from work clothes, supplies, equipment, tools or containers
2.refrain from eating or smoking in the work area
3.store supplies that contain lead safely and mark the labels with safety information
In your work area As a potter you should minimize your exposure to lead dust in the studio. Where possible, do as much of the glazing and firing process as possible at properly equipped institutions where the specialized equipment you need (e.g. kilns and casting moulds) is properly vented.
If you decide to work at home, make sure that your studio is adequately contained to prevent lead dust spreading and that it can be easily cleaned. This means working on carpets is not recommended; plastic sheeting is preferable.
Stay clean Clean all surfaces in the work area, tools and equipment regularly by wet dusting, not dry brushing or sweeping. Clean walls and windows at least monthly with sugar soap that can be obtained from a hardware store or tri-sodium phosphate (TSP) bought from an industrial cleaner stockist. TSP should be mixed at the ratio of at least 25g of 5% TSP to each five litres of hot water.
Vacuum only with vacuum cleaners equipped with HEPA (High Efficiency Particulate Air) filters, which will remove fine lead dust from the workroom. Wet mopping is the next best alternative if a vacuum cleaner fitted with a HEPA filter is unavailable.
Dispose of waste properly Dispose of waste materials containing lead, including water contaminated by wet mopping, according to State/Territory or local government regulations. The water should be placed in a strong, securely sealed container. Do not pour water down drains or on to the garden.
Products using lead glazes Lead-fluxed glazes and colors can be acid-resistant providing that they are properly formulated, applied and fired. The main risk to your health occurs when unknown or incorrectly formulated products are used.
When mixing glazes, use a half-face particulate or air-purifying respirator that meets Australian Standard 1716. It should be fitted with a P1 (dust) or P2 (dust and fumes) filter, both of which capture small particles of lead. The respirator can be bought from major hardware stores. Replace the filter regularly.
Wear protective clothing and eye protection at all times. Wash clothes separately from the family wash and shower and wash your hair as soon as possible after your work even though they are not resistant to food acids.
Clear glazes that are commercially available are safe when used according to the manufacturer’s instructions.
When coloring oxides are added to glazes to create an effect, the fired product is less likely to be acid resistant. Indiscriminate mixing of glazes or glaze components should be avoided.
Follow these precautions Use only ready-made glazes and decorative colors from a reputable source and read their metal release characteristics.
Additions to products are not recommended because they could alter the formulation and introduce unknown durability factors.
Fire the glazes to the recommended temperature. Under-firing to produce special effects could lead to poor durability.
Do not blister lead glazes on functional ware.
Remember the use of lead frits in glazes fired above 1170°C is hazardous because it forms lead fumes.
Make sure your kiln is safe. It should be designed, sited and operated according to statutory regulations and the recommendations of the manufacturers. Remember lead fumes are toxic.
Keep young children, pregnant women and women of childbearing age well away.
Avoid using raku-fired pottery for food or drink containers. The low-firing temperature reduces durability, particularly under acid conditions.
Disclaimer This information is by no means a complete. It is a guide only. It remains the duty of each individual handling these and other substances to insure that the proper safety standards are met, and that he/she is fully informed on the levels of toxicity of the various substances he/she is using. For more information, refer to the relevant literature available on each ingredient.
The above information is extracted mainly for government environmental bodies.