Reference Library - Composition
| 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. |
| White, R.H. | "Application of Electron Microscope and X-Ray Analyses to Identification Techniques for Stamps and Proof Papers", The United States Specialist, Parts I, II and III, Vol. 60, Nos. 4, 6 and 8. pp. 187-191, 299-305, 419-427. |