Lead-containing glazes

When these pigments are used with lead-containing glazes, care should be exercised to use lead-safe glaze materials (see Lead compounds, industrial toxicology). 

As the Romans ingeniously introduced lead water pipes, it is likely that their water, carried in these pipes, was contaminated with lead as it still is today, especially in areas of soft or acidic water. The use of lead glazes in pottery and, even more importantly, lead cooking pots were other contributory factors. Thus the lead was dissolved from the surface of the lead pots or from the lead-containing glaze on pottery. Analysis of the bones of Romans from the time of their empire has shown high levels of lead, sufficient to cause lead poisoning. 

Acute ingestion. Because even small items (eg, a paint chip or a sip of lead-containing glaze) may contain several hundred milligrams of lead, gut decontamination is indicated after acute ingestion of virtually any lead-containing substance. 

Food contamination may result from transmission of lead from glaze, enamel, or tinning on kitchen dishes, or from the lead on surfaces of containers or pipes used for storage, processing and transportation of food products. The occurrence of lead in food can also result from environmental contamination, as plants and animals may assimilate lead during growth and incorporate it into their tissues. The level of lead found in plant tissues is proportional to its concentration in the environment, and in cases of animals, the feed and water supplies also play important roles (Vreman et al., 1988 McLaughlin et ah, 1999 Sedki et ah, 2003). 

Lead poisoning is still a problem today in some countries because lead and all of its compounds are toxic to humans. In certain parts of the world, lead compounds are still used as glazes and paints. It is believed that lead poisoning must have been a major problem for the Romans as the result of the widespread use of lead and lead-containing materials. Human remains from archaeological excavations in that region show a high concentration of lead. 

T7or the past 10 years extensive effort has been devoted to studying the isotopic ratios of the element lead contained in glasses, glazes, and pigments and from bronze, gold, and silver items from the ancient world... 

Opaque glazes contain opacifiers either in frit (zircon, fluorides) or as a secondary component (Sn02). They are used wherever the body colour is to be covered or to attain pastel colour shades, in particular in building ceramics. Lead-free glazes are likewise given preference in industrial production. 

Various arts and hobbies involve lead-containing materials. Lead is found in artist s paints (certain pigments), ceramic glazes (particularly reds), solder used in stained-glass windows, and linings in containers used for distilling homemade whiskey. Certain Mexican, Middle Eastern, and Asian folk remedies and cosmetics contain lead. 

Leadless Glaze. In the UK this is defined in the Potteries etc (Modifications) Regulations 1990 (S.I. 305) . A glaze which does not contain more than 1% of its dry weight of a lead compound calculated as PbO. Under current environmental pressures to reduce the use of lead, bismuth glaze and colour flux systems are being actively studied. Lean Clay. A clay of low plasticity the adjective lean is also applied to a body of low plasticity. 

The experience of a physician family in Illinois illustrates the typical toxicity symptoms and some common source of lead. Five of the six members of the family experienced fatigue, poor appetite, pains in the stomach, and vomiting. (One exception was the infant who was on a formula). They became increasingly irritable. The blood test disclosed severe anemia. An exhaustive search identified an earthenware pitcher as the source of lead. The pitcher was glazed with lead-containing compounds and it was insufficiently fired. It was used for orange juice container, and the acidic juice leached out the lead. 

Hair and bone analyses have revealed that lead contamination of humans in preindustrialized times was apparently higher than today. This might be due to the use in those days of lead pipes for drinking water, lead-containing tinware, and excessive use of lead salts for heavily glazed pottery used as kitchenware. 

The main use of lead metaborate is in glazes on pottery, porcelain, and chinaware, as weU as in enamels for cast iron. Other appHcations include as radiation-shielding plastics, as a gelatinous thermal insulator containing asbestos fibers for neutron shielding, and as an additive to improve the properties of semiconducting materials used in thermistors (137). 

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