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All that is, at all, Lasts ever, past recall, Earth changes, But thy soul and God stand sure, Time's wheel runs back or stops: Potter and clay endure. Of all the different types of material, ceramics might be the most difficult to define. Many would regard them as falling in a small and rather restricted group, and the only examples that come readily to mind would probably be bathroom fixtures, tiles, and the insulators in spark plugs and on telephone poles. The term ceramic actually covers a large variety of natural and artificial substances that share the desirable qualities of hardness and resistance to heat, electricity and corrosion. Just how large and how important the ceramic domain is can be gauged by some of its members: stone, brick, concrete, sand, diamond, glass, clay and quartz. If there has been a lack of understanding of ceramics, it is excusable because even dictionary definitions tend to be rather narrow. We find them restricted to either pottery or porcelain in most cases, and even the better efforts usually go no farther than ‘products of industries involving the use of clay or other silicates’. The word ceramic actually comes from the Greek word keramos, which means burnt stuff. This is too broad a term to be useful here. The best working definition uses a combination of chemical and physical criteria. [ABSTRACT FROM AUTHOR]