Studies in Ancient Glasses and Glassmaking Processes. Part III. The Chronology of the Glassmaking Constituents
JSGT 1956 V40 T039-T052
By utilising all known records from the earliest times and examining them in the light of chemical and spectrographic analyses of ancient glasses, tables have been drawn up showing the earliest literary references to, and also the probable first intentional use of, the various commonly used glassmaking substances. The earliest-mentioned substances in recipes for glazes in a Babylonian document at least as early as 1700 B.C. were saltpetre, lime, copper, and lead; and on Assyrian (Nineveh) tablets of seventh century B.C. these same substances again appear together with alkali (in the form of ash from the plant salicornia), antimony, and arsenic; although in respect of the last-named substance, its absence save for traces in a very few cases, from all analyses of ancient glasses dated up .to the end of the seventeenth century A.D. casts doubt on the correctness of its identification on the tablets. The meaning of nitre, and the slow evolution of the modern terms saltpetre, soda, and potash are described. The differences between soda and potash were not realised or established until the eighteenth century A.D. The use of borax in glassmaking was first mentioned in 1679 and of sodium sulphate in 1764. From numerous analyses, it is evident that the ancient glasses were predominantly of the alkali–lime–magnesia–alumina–silica type, and the analysed lead-containing glasses do not constitute more than ten per cent of the total; nevertheless until the eighteenth century A.D. the glassmakers did not know that their glasses contained lime and magnesia. It is true that the Babylonian chemical text quotes lime as present to about two per cent in the recipe for a glaze, and the Nineveh tablets quote three recipes for glasses containing lime between 0·9 and 0·2%, whilst Pliny speaks of shells as having been introduced into the glassmaking mixture by some glassmakers; but these small additions are entirely inadequate to account for the five to twelve per cent of CaO in ancient glasses of many periods and places, and in medieval glasses sometimes exceeding twe.nty per cent. Moreover, for sixteen centuries of the Christian era, there is no reference to lime as an essential constituent for glasses, and the most competent authorities throughout the seventeenth century (Merret, Kunckel, and de Blancourt) advised against its suitability for inclusion. Lead is mentioned as a constituent for glazes in the Babylonian chemical text of 1700 B.C. and once in the recipes for glasses on the Nineveh tablets. Subsequently it is given as a constituent of glass for rings by Theophilus in the tenth century A.D. and more fully described in glassmaking by Heraclius in the twelfth-thirteenth centuries. Examples of lead glasses, mainly opaque and coloured, have been found of different periods from 1400 B.C. onwards. Barium in large concentrations has been found in Chinese glass beads dated about 200 B.C. but no other known example occurs of its use until J. W. Dobereiner intentionally introduced it into optical glass in 1829. Of the colouring elements iron, cobalt, copper, and manganese, copper is mentioned in the Babylonian chemical text of 1700 B.c. and in the Nineveh tablets, and appears in specimens of glass throughout the whole 3000–3300 years under review. Cobalt is present much less frequently than copper in specimens from 1400 B.C. onwards and only received its first mention in the literature by J. Kunckel in 1679. Manganese occurs in a large proportion of the analysed ancient glasses from about 1400 B.C. onwards, mainly in coloured glasses. Whether or not Pliny mentioned manganese in the first century A.D. is obscure. It was first clearly defined and its functions described by Biringuccio in 1540. Although there are earlier references to gold as producing red colours in glasses, the first description of a process for its use is that by A. Neri in 1612.
W. E. S. Turner
