When all else fails, lead-210 testing may provide the only concrete evidence that a metal object is not an antique. If the object contains this form of lead it cannot be older than, roughly, 100 years.
Classification of some metal objects, as modern or old, cannot be clearly established based on composition and metallography. These objects require a test for lead-210 (Pb-210, 210Pb), a radioactive isotope of lead. This substance has a half-life of roughly 22.3 years. If Pb-210 is detected in a sample of metal, the material cannot be older than roughly 100 years, maximum.1 The absence of Pb-210 does not necessarily indicate an age older than 100 years, as the metal might never have contained the substance. However, even high-caliber forgeries of Chinese bronzes have often been found to contain this isotope, and lead-210 analysis has successfully removed many exceptional forgeries from the market. In our experience at TK, the objects that have tested positive for Pb-210 were already suspect, based on metallography and/or composition.
Numerous laboratories around the world perform lead-210 analysis on organic samples. However, only one facility is currently known to regularly test metals. The sample size is dependent upon the material's lead content. The higher the percentage of lead, the smaller the sample needed. At TK, the shavings from cutting or drilling of the metal are sealed in a container and sent to Prof. Dr. Ernst Pernicka, of the Technical University of Freiberg (Freiberg, Germany) for analysis. Documentation includes photographs of the overall object and the sample site, object description and purported age.
Though more commonly performed on organic materials, lead-210 testing may be used on samples of metal that contain lead. If a metal sample is found to contain the lead-210 isotope it cannot be more than, roughly, 100 years old. This analytical technique is not used to authenticate antiquities but to detect modern reproductions.
Flett, Robert. [date unknown]. Flett research home page [Internet]. Winnipeg (Manitoba): Homepage for Flett Research; [updated 2003 Oct 8; cited 2003 Nov 25]. Understanding the Pb-210 method. Available from: www.flettresearch.ca/Webdoc4.htm
[USGS]. [date unknown]. Western lake catchment systems - Bear Lake region. [Internet]. Washington (DC): U.S. Dept of the Interior, USGS; [updated 2003 Jun 12; cited 2003 Nov 25]. Methods used at Bear Lake: Dating: 210Pb (lead 210) dating. Available from: www.climchange.cr.usgs.gov/info/lacs/lead.htm The Bear Lake Homepage is available at: www.climchange.cr.usgs.gov/info/lacs/index.html