Abstract: From the fifteenth century onwards, Chinese porcelain was imported into Europe in increasing amounts and the potential profits to be gained from a European porcelain industry were widely appreciated. Much experiment went into the development of porcelain bodies and, because true hard-paste porcelain proved difficult to achieve, a number of chemically unrelated soft-paste porcelains were developed. This was especially true of England where the production of hard-paste porcelain did not begin until c. 1770. In 1740 porcelain-making was still in an experimental stage in England but by 1750 all the three principal types of soft-paste porcelain were in production. These three types were glassy porcelains similar to the French plite tendre, soapstone porcelains which employed ‘soapy rock’ from the area of the Lizard peninsula, and bone-ash porcelains which are characterized by the presence of calcium phosphate derived from bone. The name glassy porcelain may originally have been merely a descriptive term coined by collectors to describe this particular type of soft-paste porcelain but it is a very apposite one, since the elements involved are those commonly employed in glassmaking, that is silica, the alkaline earths, the alkalis, alumina and lead. Glassy porcelains were the only soft-paste porcelains developed in France where their production dates from the seventeenth century at Rouen and from the early eighteenth century at Saint Cloud (Charleston 1968,215), thus predating porcelain-making in England by several decades. It has often been said that the production of English glassy porcelains must have been based on the French model, but there is little direct evidence and the earliest English porcelain contained significant amounts of lead. The use of lead in a porcelain body seems to have been a particularly English innovation as was the production of high-lead vessel glass; no lead compound is included in the list of raw materials for French pbte tendre quoted by Brongniart (Brongniart 1854, 460), who was manager at Sevres from 1800 to 1847. The manufacture of a glassy paste had begun at Chelsea by 1745, it continued there until 1758, at Derby until c. 1764 and at Longton Hall until 1760 and, subsequently, by the same potter, at West Pans until 1767. Glassy porcelains had a relatively short life in England because, though beautiful, they were very difficult to fire without considerable wastage. Apart from the fact that it is white and apparently infusible, it is not obvious why bone-ash should originally have been considered as an ingredient of porcelain. It was in plentiful supply as an end-product of glue boiling but seems to have been little used in industry except in the manufacture of crucibles for assay; it had also been used to opacify glass but on a very limited scale. The second Bow patent of 1749 (Jewitt 1878, 113) seems to hide the use of bone-ash under the term ‘virgin earth’; the specification describes ‘virgin

Abstract: This paper is the text of the inaugural lecture given by the author in the Ashmolean Museum Lecture Theatre on 23 October 1990 following his appointment in October 1989 to the Edward Hall Chair of Archaeological Science, at the University of Oxford

Abstract: The effects of weathering and lichen activity on tuffs from historic sites in the Cappadocia region of Turkey have been investigated using x-ray powder diffraction, optical microscopy, scanning electron microscopy coupled to an EDAX system, and instrumental neutron activation analysis on the tuff samples. Mineralogical and chemical variations from the surface toward the interior part of the rock explain the visible forms of deterioration, such as color change, granular disintegration, exfoliation, and mineral deposition observed in the field. A maximum depth of deterioration equalling 6-8 cm is identified. This conclusion is based on the observable effects of weathering on feldspar and biotite crystals, together with the variations in some trace element contents.