# The Environmental Protection (Prescribed Processes and Substances) Regulations 1991, 

Extent: E+W+S

(a) Firing heavy clay goods or refractory material (other than heavy clay goods) in a kiln where the process does not fall within a description in Part A of this Section.
(b) Vapour glazing earthenware or clay with salts.
In this Section—
“clay” includes a blend of clay with ash, sand or other materials;
“refractory material” means material (such as fireclay, silica, magnesite, chrome-magnesite, sillimanite, sintered alumina, beryllia and boron nitride) which is able to withstand high temperatures and to function as a furnace lining or in other similar high temperature applications.

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Source: https://www.legislation.gov.uk/uksi/1991/472/schedule/1/part/3/crossheading/section-36-ceramic-production-2 (the official version)
Page: https://openlegislation.uk/environmental-protection-prescribed-processes-and-substances-regulations-1991/schedule-1/part-3/crossheading-section-36-ceramic-production-2
Contains public sector information licensed under the Open Government Licence v3.0. Source: legislation.gov.uk, The National Archives.