A sequel to the classic text Thermoluminescence Dating (1985) by the same author, An Introduction to Optical Dating follows very much the same format as its predecessor. Indeed the continuation of style is, for me at least, the most disappointing element of his volume in as much as it again utilises the addition of a 'Technical notes' section at the end of each chapter. This is a style that can be frustrating, continuity of reading being disrupted by having to move to and from appropriate technical notes whilst part way through a chapter. A more 'readable' style would have been insertion of sidebars alongside appropriate passages in the text.
Notwithstanding this criticism, however, the book is destined to be an important text to any practitioner of luminescence dating. Optical dating is a fairly recent innovation (Huntley, et al. 1985), and the announcement of its development coincided with the publication of Thermoluminescence Dating ; hence it received only the briefest of notes in that volume, and likewise in Science-Based Dating in Archaeology by the same author (1990). The progress in the technique in the thirteen years since its inception has been reflected in the wealth of papers published on the subject, and a single text summarising its development is very welcome.
The volume itself is remarkably up to date. Developments in optical dating are very rapid and the inclusion of many references from 1998 puts An Introduction to Optical Dating at the forefront of the discipline. Simultaneously, the timing of its publication has allowed the technique to develop sufficiently to prevent the book being rapidly outdated. The book itself comprises a brief prologue followed by seven chapters and five appendices. The prologue serves to establish the position of optical dating in relation to other absolute dating techniques, and this is followed by two introductory chapters which outline the basic principles behind luminescence dating and the nature of the ionising radiation responsible for the accumulation of the luminescence signal. The latter part of the second chapter is dedicated to artificial irradiation in the laboratory, including important references to the possible health hazards of working in close proximity to radiation sources.
In the subsequent two chapters the author moves on to explain how an optical date is obtained, detailing sample collection and preparation, dosimetry, current commercially available luminescence dating systems, and palaeodose evaluation. Whilst some of this may appear at times a little too basic to proficient practitioners, it is a welcome inclusion in an overtly scientific publication, in that it ensures that even the most fundamental elements are presented to all, regardless of experience. The absence in palaeodose evaluation of a conclusion as to which of the many techniques is the one to use may appear a little vague, but this reflects the nature of the discipline rather than any omission on the part of the author. The fairly short history of optical dating, allied to the complexity of the technique and subject materials, means that the technique still remains in a state of flux, something reflected in the fact no optimum method is cited.
Chapter five is used to illustrate some of the depositional environments from which material has been sampled and subjected to optical dating. As stated by the author at the start of the chapter, the examples cited are 'not a comprehensive review' (108), but they do demonstrate the broad potential of the technique. Importantly, whilst aeolian deposits are identified as those most amenable to the technique, a necessary warning against the blind assumption that all such sediments relate to adequate bleaching and correct optical-series luminescence dates is included, which the author illustrates with an example of loess from British Columbia that produced less than ideal results. At times the transition between subsections within this chapter feels abrupt but this reflects the need to balance content and chapter size, and it is essential that this chapter is treated as a summary leading to further reading. An attempt to broaden the scope of this section could have justified one, if not several, additional volumes.
The sixth chapter considers the nature of re-setting the signal upon exposure to light, summarising the variability of the time taken to bleach different types of material adequately, according to depositional context and prevailing light conditions. As a natural progression from this, the author then moves on to outline some of the ways in which practitioners have attempted to accommodate partial bleaching, both for material that is equally, but partially, bleached and for material that comprises a mix of grains that have received various degrees of light exposure. As the scope of optical dating expands to incorporate sediments from ever more diverse environments, the importance of dating partially bleached material is likely to grow, and the inclusion of a chapter on the subject is essential. It is also likely that partial-bleaching techniques are likely to develop much further, thereby making this chapter one that is at risk of becoming fairly rapidly outdated, though the inclusion of the most recently published developments in partial-bleaching methodology provides the basis for further research.
Chapter seven details the principles of pre-heating in optical dating, outlining its disadvantages and advantages. The significance of pre-heating is illustrated by its warranting a full chapter, and the disparity of views of which pre-heating regime is appropriate is well documented here. The evidence presented from a variety of sources leads one to conclude that the adoption of universal pre-heats for all samples, a practice often adopted in the past, is a simplistic approach. However, as with the preceding chapter, the inclusion of the latest research still leaves the impression that here is an area that has far to go before a conclusive methodology is determined.
Finally, and again following the style established in Thermoluminescence Dating, the author includes several appendices detailing radioactivity, filters, undesirable signal components, anomalous fading, and sensitisation of the 110° C peak. Some of these appendices are developed from similar sections in the earlier volume whilst others are new and more specific to optical dating. As with the 'Technical notes' sections, better continuity might have been achieved by their inclusion earlier within relevant chapters wherever possible (e.g. Appendix A: radioactivity data, could have been included in chapter 2: Basic notions: radioactivity and irradiation, and Appendix B: Optical filters, could have been included in chapter 4: Palaeodose evaluation).
In summary then, An Introduction to Optical Dating is a very scientific tome that really would be of limited interest to those outside the discipline of luminescence dating. A better introduction to anyone with a general interest in absolute dating techniques is Science-Based Dating in Archaeology (1990). However, as a companion volume to Thermoluminescence Dating (1985), this volume will prove invaluable to luminescence-dating practitioners. Perhaps the best summary of the whole is to say that its contents make me wish that I was starting my research now, rather than three years ago when no such text was available.
Aitken, M.J. 1985. Thermoluminescence Dating. London: Academic Press.
Aitken, M.J. 1990. Science-Based Dating in Archaeology. London: Longman.
Huntley, D.J. et al. 1985. Optical dating of sediments. Nature 313: 105-7.
About the reviewer
Dave Sainty is in the final year of his PhD at Sheffield researching the feasibility of applying luminescence dating to cave sediments. Having spent three years working in the dark, he is now preparing to face the outside world once again.
He may be reached by e. mail on <firstname.lastname@example.org>>.
Copyright © D. Sainty 1998
Copyright © assemblage 1998