Archaeologists date artifacts via both scientific carbon dating methods and sometimes using typology (relative chronological sequence – to match an artifact already documented within a well-established typological scheme) in order to determine its specific period. The most useful is of course radiocarbon (C14), although it does have its limitations, especially with regard to accuracy (due to poor sampling measures and thus contamination, as well as careless interpretation). On the whole, however, it does offer a broad pattern with similar types of finds being found relative to particular time periods. With regard to studies of Iron Age Celtic art, a great emphasis is still put onto the work of Paul Jacobsthal, which was carried out more than six decades ago. Four main styles were identified in his classic Early Celtic Art (1944) that are now generally accepted for the La Tène period: the Early Style, the Waldalgesheim Style, the Plastic Style, and the Sword Style. However, since that study, there have been numerous new and unusual finds and it is important to discuss further the implications of such unearthings. There is an interesting paper (published in 2004) that discusses this issue, although you will have to register to gain access to the full journal article. It is, however, possible to view the abstract without any prior registration and I have also pasted relevant information below for ease of access:
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“A New Approach to Early Celtic Art” from the Proceedings of the Royal Irish Academy – Volume 104, 2004, Pages 107-129: http://bit.ly/UMr6F
Publisher The Royal Irish Academy
ISSN 0035-8991 (Print) 2009-0048 (Online)
Issue Volume 104, Volume 104 / 2004
DOI 10.3318/PRIC.2004.104.1.107
Pages 107-129
Online Date Friday, August 24, 2007
PDF (1.1 MB) Authors Otto–Herman Frey Abstract All modern studies of early Celtic art begin with the work of Paul Jacobsthal. In the sixty years since his magisterial study, however, there have been many new discoveries and there has been much discussion concerning the deeper meaning of Celtic art. Particularly significant in this regard are the two recently discovered Early La Tène burial mounds on the Glauberg in Hesse in Germany. Not only did these burials yield bronzes of major significance, but a unique, almost life-sized human carving displaying weapons and personal ornaments was also found. The finds from the Glauberg shed much new light on the nature of early Celtic art. The influence of the Estrucans of north Italy is especially evident.
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Paul Jacobsthal’s work, “Early Celtic Art”, may be obtained by following this link: http://bit.ly/1NxOk9, although I must inform you that it is a little on the expensive side now that it has become a collector’s item.