Lead in ceramic crockery and pottery making
Lead in ceramic crockery and pottery-making
Lead is a toxic substance that can affect people of any age. It is especially harmful to children, pregnant women and unborn babies. Lead accumulates in your body, so even small amounts can pose a health hazard over time. Lead used in ceramic glazes or in decorative paints covering the surface of ceramics can be a health hazard for potters, and for people using their products. This is because the lead can get into food and drink prepared, stored or served in the crockery.
Lead in ceramic crockery
Lead has long been used in ceramic ware, both in glazes and in decorations. When used in a glaze, lead gives a smooth, glasslike finish that allows bright colours and decorative patterns to show through. It is often associated with rich or intense colours.
There are many kinds of ceramics used for cooking, serving or storing foods and liquids. You cannot tell whether a dish has lead in it just by looking at it, however, some types of dishes are more likely to have lead:
• Traditional glazed terra cotta (clay) dishware made in some Latin American countries, such as Mexican bean pots;
• Highly decorated traditional dishes used in some Asian communities;
• Homemade and hand-crafted tableware, unless you are sure that the maker has used a lead-free glaze;
• Decorations on top of the glaze instead of beneath it. If the decorations are rough or raised, if you can feel the decoration when you rub your finger over the dish, or if you can see brush stroked above the glazed surface, the decoration is probably on top of the glaze. If the decoration has begun to wear away, there may be a greater lead hazard;
• Antique tableware handed down in families or found in antique stores, markets and garage sales;
• Corroded glaze, or a dusty or chalky grey residue on the glaze after a piece has been washed. Tableware in this condition may represent a serious lead hazard – stop using it at once.
Lead is rarely found in plain white dishes. Lead-containing glazes or decorations on the outside of dishes or non-food surfaces are generally safer to use. The only way to determine if certain crockery has lead is to test it. Home test kits can tell you if the dishes have leachable lead. These tests are most useful in detecting high levels of lead.
Home test kits use a “quick colour test” system and contain a chemical that turns a certain colour when applied to a surface that contains significant quantities of leachable lead. These test kits can usually be found at hardware stores. These test kits are especially useful in detecting high levels of lead in crockery. However, they only detect the presence of lead, not the amount. The only way to determine the exact amount of lead that the crockery leaches is to send it to a laboratory for testing. In addition to being expensive, this can also damage the item.
How to reduce exposure to lead from crockery
The safest practice is to not use crockery that you are unsure of. In particular, if you do not know whether a dish contains lead, do not use it in your everyday routine. This is especially important for crockery used by children, pregnant women, or nursing mothers.
Some guidelines to help you stay safe:
• Do not heat food or drink in crockery that may contain lead. Cooking or microwaving speeds up the lead-leaching process.
• Do not store food or drink in dishes that may contain lead. The longer the food/drink stays in contact with a surface that leaches lead, the more lead will be drawn into the food/drink.
• Do not put highly acidic food or drink in crockery that may contain lead. Acidic food and drink leach lead out of dishes much faster than non-acid foods. Common acidic foods include citrus fruits, apples, tomatoes, soy sauce and salad dressing. Many drinks are also acidic; such as fruit juices, soft drinks (especially cola drinks), alcohol, coffee and tea.
• If a dish contains lead, using the dishwasher can damage the glazed surface. This can make it more likely for lead to leach into food the next time it is used. In some cases, lead may also contaminate other dishes in the dishwasher.
Occasional use of leaded crystal will not expose you to large amounts of lead, unless liquids have been stored in a leaded crystal container. Children should never eat or drink out of leaded crystalware. Do not store food or alcohol in leaded crystal decanters or containers. The longer the food or drink sits in crystalware, the greater the chances are that lead will leach into it. In addition, the amount of lead that leaches into the food or drink will increase with time.
The dangers of lead in pottery-making
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.
Lead-free glazes and low-solubility lead-bisilicate glazes made with frits have lower lead-release figures that are well within international standards. These products are readily available from most major suppliers. Lead borosilicate frits have a higher lead-release figure and 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 minimise 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 specialised 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.
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. Use a high-phosphate solution (containing at least 5 per cent trisodium phosphate, also known as TSP) or other lead-specific cleaning agent.
TSP should be mixed at the ratio of at least 25g of 5 per cent TSP to each 5 litres of hot water. TSP can be bought from industrial cleaner stockists. Sugar soap that contains TSP is available from hardware stores and supermarkets.
Note: Not all brands of sugar soap contain TSP and ingredients are not required on the labels—users will need to check the manufacturer’s website to ensure TSP is present. 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 colours can be acid-resistant, provided 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. Clear glazes that are commercially available are safe when used according to the manufacturer’s instructions.
When colouring 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 colours 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.