Roman Glassmakers Newsletter 7: January 2005

Core-formed Glass

(Photographs of the palm kohl tube being made are courtesy of Paul T. Nicholson)


An original palm kohl-tube, c.1400-1225 BC. From Goldstein, S. (1979) 'Pre-Roman and Early Roman Glass in The Corning Museum of Glass' Corning: New York, cat. no. 24, inv. no. 71.1.4

Core-forming is the process of coating a form on the end of a rod with molten glass to make a vessel. It may be decorated, and a rim, handles and a foot may be applied.

The technique is related to one of the methods of bead-making, where molten glass is wound around the tip of a mandrel to form the bead. Often, it is subsequently decorated.

The origin of core-forming is not precisely known but it is possible that it may have developed in the Kingdom of Mitanni, a Hurrian state of the mid second millenium in northern Mesopotamia and northern Syria. By the 15th century BC the technique was well established in an industry producing high-status glass ornaments and vessels in Eighteenth Dynasty Egypt, possibly introduced as a result of trade or military campaigns.

Core-forming lasted well into the Ptolemaic period, and was eventually superceded by glassblowing.

The material forming the core has been the subject of research (Bimson and Werner 1969 - two articles) and experiment (e.g. Schuler 1962, Labino 1966, Gudenrath 1991 and Stern and Schlick-Nolte 1994).

An original amphoriskos, c.1400-1350 BC. From Grose, D. (1989) 'Toledo Museum of Art - Early Ancient Glass' Hudson Hills Press: New York, cat. no. 5, inv. no. 51.405

Bimson and Werner's analyses (of 62 samples) indicate that core material from 14th century Egypt is primarily a mixture of burnt out organic matter and 'a flaky mass of dark brown material' - probably very fine silt or clay, which appears to have been coated with a powdered limestone and clay (or re-used core material) slip. The outer slip may function as a release agent, easing the task of removing the core.

The evidence from later cores (two examples from Naucratis, in the Petrie Collection, dating from c.500 BC) indicates that sand was being used, possibly replacing the organic material of the earlier cores. This does not rule out the continued use of organic matter in later cores.

There are several theories regarding the methods adopted by ancient glassworkers of applying glass over the core:

The latter two seem the most likely of these four methods, if only for speed and simplicity. Of these two, we favour trailing, as it requires smaller amounts of glass to be molten, allowing the use of smaller furnaces and allowing lower temperatures, which were perhaps more suited to ancient glassworking. Labino worked using a side entrance to his furnace, trailing the glass onto the core inside the furnace, immediately above the crucible. We work above the furnace, using the exhaust gases and radiation to heat the glass and core; or away from the furnace. This gives more control over the temperatures of the glass and core. It is also worth noting that more than one method may have been used at any one time.

Stern and Schlick-Nolte see a change, through time, in the technique for coating the core, moving from crushed glass being applied to the core in early core-forming to glass being applied as a trail in later vessels. They cite examples of trailing on the bases of two 5th and 4th century vessels and note the absence of evidence for trailing on early examples (Stern and Schlick-Nolte 1994, p.31, p.40 & ill.22, cat. nos. 43, 51).

For a detailed summary of the history and technology of glassworking during this period, see:

Nicholson, P. T. and Shaw, I. (eds.) (2000) 'Ancient Egyptian Materials and Technology' Cambridge University Press. Ch.8, 'Glass'. This book has comprehensive bibliographies on the topics covered.

For the results of analyses of Egyptian core material, see:

Bimson, M. and Werner, A. E. (1969) 'Two Problems in Ancient Glass: Opacifiers and Egyptian Core Material' in J. Philippe (ed.) 'Annales du 4th Congres International du Verre, Liege, pp. 262-266; and

Bimson, M. and Werner, A. E. (1969) 'Problems in Egyptian Core Glasses' in Charleston, R. J., Evans, W. and Werner, A. E. 'Studies in Glass History and Designs' Sheffield: Society for Glass Technology, pp. 121-122.

For practical core-forming experiments , see:

Schuler, F. (1962) 'Ancient Glassmaking Techniques. The Egyptian Core Vessel Process' in Archaeology 15, pp. 32-37.

Labino, D. (1966) 'The Egyptian Sand-core Technique: a new interpretation' in Journal of Glass Studies 8, pp. 124-127.

Gudenrath, W. (1991) 'Techniques of Glassmaking and Decoration' in Tait, H. (ed.) 'Five Thousand Years of Glass' London: British Museum Press, pp. 213-241.

Stern, E. M. and Schlick-Nolte, B. (1994) 'Early Glass of the Ancient World 1600BC - AD 50' Ostfildern: Verlag Gerd Hatje.

Our Experience:

When we were asked to demonstrate ancient core-forming for television, we had to start from the basics. After about one month of practise we reached the level where we could reproduce Egyptian New Kingdom vessels to a reasonable standard.

A core-formed palm kohl tube A core-formed palm kohl tube

Mark Taylor and David Hill

0044 (0)1264 889688

Our new e-mail address is vitrearii @ romanglassmakers . co . uk

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