Spectroscopy: X-Ray Diffraction

Liston, E.M. “The ‘China Clay’ Variety of the 1908-1910 Washington-Franklin Issues?,” The Collectors Club Philatelist, Vol. 84, No. 2, March-April 2005, pp. 105-112 and Vol. 84, No. 3, May-June 2005, pp. 141-146.