Bulletin Number Four 1986

Yeung Shui Sang Laboratory fo r T L Dating o f Ancient Ceramics The Yeung Shui Sang Laboratory for Thermo- luminescence (TL) Dating of Ancient Ceramics was established in early 1986 with a generous donation from Mr. Yeung Wing-tak and his brothers. It is well known that fine imitations of antique Chinese ceramics very often defy scholars, collectors and curators who rely on typological or stylistic con siderations for authentication and dating. TL dating method provides an alternative to get over the impasse. More important, as it can be applied to ceramics directly to give absolute dating, it will undoubtedly contribute greatly to the understanding and knowledge of ancient Chinese ceramics. The Establishment o f the Laboratory Since July 1982, the Department of Physics and the Art Gallery have been collaborating on researches on TL dating for ancient ceramics. Under the supervision of Dr. L.S. Chuang of the Department of Physics, a computerized TL measuring system has been fabricated. New methods of dating for pottery using this system have also been developed. The resulting TL ages of pottery pieces tested were in good agreement with the corresponding archae ological ages within fifteen percent discrepancy (Fig. 1). At present, collectors and archaeologists in Hong Kong and in the neighbouring regions can only resort to the TL dating service provided by the la boratories in the United Kingdom and USA. This long distance service is both time-consuming and expensive, not to mention the possibility of breakage during shipping. The establishment of a laboratory for TL dating in Hong Kong is undoubtedly a solution to this problem. Moreover, being in close proximity to the archaeological sites in South China, we can carry out measurements of the environmental dose rate in situ as frequently and accurately as desired. This will help to ascertain not only the date of archaeological finds more accurately but also the date of different strata of the sites which are hitherto undatable. Realizing the importance of scientific dating towards the study of ancient ceramics, Mr. Yeung Wing-tak, a well-known collector of Chinese ceramics, and his brothers generously donated one million Hong Kong dollars for the establishment of the Yeung Shui Sang Laboratory for TL Research. Subsequently a management committee for the laboratory was formed, with Mr. Yeung Wing-tak as Chairman. Dr. L.S. Chuang was appointed Director of the laboratory. The laboratory aims (1) to research for the improvement of TL methods for dating ancient ceram ics and to publish the results of the research; (2) to collaborate with other museums and archaeological institutes in China, Japan and Southeast Asia, in TL projects; and (3) to provide dating and authentication service to the public with certification. The Principle o f T L Dating TL dating method was first developed at the Research Laboratory for Archaeology and the History of Art, Oxford University. It has provided dating service of ancient pottery for a number o f years, but the dating service of porcelain has begun only recently. However, the dating of both pottery and porcelain by this method follows the same principle. The fabric of ceramics is a matrix of amorphous clay in which a variety of crystalline minerals of various grain sizes are embeded. Such crystals may act as a source of TL. When the ceramic is fired in the kiln during manufacture, it reaches a temperature high enough to discharge all previously stored TL energy —a process that may be compared to setting a clock to zero time. Subsequently the ceramic is subjected to a small amount of ionizing radiation year by year. Much of this comes from traces of radioactive isotopes in the ceramic itself; some derives from similar isotopes in the burial medium, and a minor proportion from cosmic radiation. Such pro cesses restore TL energy to the ceramic. When a sample of the ceramic is heated in suit able apparatus, the intensity of TL can be measured in the form of a 'glow curve' (Fig. 2). The TL repre sented by the glow curve is proportional to the total archaeological radiation dosage received. The annual radiation dosage received by the ceramic can be determined from the measurement of the radioactive contents of the specimen and its surroundings. There fore, the time that has elapsed since the manufacture of the specimen can be calculated according to the following basic age equation: Work in progress We have already developed reliable methods using modified fine grains and quartz inclusion for the dating of pottery. However, these methods cannot be applied directly to stonewares and porcelain because of their different types of fabric. At present, we are engaging in the following work: 20 RECENT DEVELOPMENTS