Ceramic rooms involve the use of materials in ‘plastic’ and slop form. These materials can provide hazards through slipping and dust inhalation. Good housekeeping is essential and this can be maintained with a properly planned cleaning regime and a well managed ceramics studio.
The use of raw lead compounds is forbidden in schools (DFE Administrative Memorandum 517). Glazes containing more than five per cent soluble lead should not be used at all in schools, and strict precautions should be taken with other glazes. However, the presence of heavy metal compounds such as lead or cadmium in glazes does not constitute a hazard providing they are correctly formulated, applied and fired.
Glazes Subject to Acid Attack
Glazes applied to pottery such as plates, mugs and dishes that may be used for food and drink must be carefully chosen, since some are subject to acid attack resulting in the release of lead, cadmium or other toxins. Copper should not be added to any glaze intended for food contact surfaces. Blending glazes or components should be avoided, as this can result in products with unknown acid durability. In such circumstances a metal release test should be carried out to determine whether the necessary safety standard has been achieved (see BS6748 (1986) specification for Limits of Metal Release from Ceramic Ware, Glassware, Glass Ceramic Ware and Vitreous Enamel Ware).
Information on the current lead and cadmium release limits can be obtained from local authority trading standards and consumer protection departments or British Ceramic Research Limited.
Dust from Dry Clay
Dust from dry clay and glazes constitutes the chief hazard in a ceramics studio. Good management and cleaning will reduce the hazards considerably. Dry materials should be stored in sealed containers, and both wet and dry spillage should be cleaned up immediately.
There are many ceramic materials other than lead that are toxic, and teachers should ensure that information is supplied when they are bought and the suppliers' instructions are strictly observed. It is essential that all materials are properly labelled and stored, and that appropriate warnings are included in the labelling. One of the main reasons for insisting upon the regular and thorough washing of hands is to avoid toxic hazards.
Glazes in General
Eyes and skin should be protected when using glazes, and good washing facilities are essential. Food and drink should not be allowed in areas where glazes are being used. Glazes containing chromium are severe skin irritants. During glaze preparation dry materials should be added to water, not water added to the dry material, to minimise dust.
The reason for insisting upon adequate ventilation or forced LEV over a kiln is that during firing various glaze materials break down. For example, Cornish stone releases fluorine and wood ash produces sulphur dioxide if not thoroughly washed; enamel media and lustres produce acrid fumes during the initial stages of firing; and noxious, sulphurous fumes are released by some fire clays during firing.
Glazes, which are fired for too long or at too high a temperature, can release volatile materials into the atmosphere. For example, lead becomes volatile at, around 1180°C, so a low-solubility lead glaze would release lead-bearing fumes.
No food or drink should be taken into or consumed in pottery/ceramics areas. Pupils must wash their hands thoroughly with soap before leaving the ceramics studio and ensure their hands are clean before they eat and drink.
CLEAPSS Resource - GL245 Ceramics in schools
CLEAPSS guidance - MRAT - 144 - Ceramic Clay and Dusts
CLEAPSS guidance - MRAT - 145 - Ceramic Glazes and Colours
The HSE produce guidance on the safe use of silica in ceramics. The guidance can be viewed here.