FEPA News

FEPA NEWS 45 48 Developments in Philately Fig. 3c: Postal card dated 9 August 1883 from Constantinople to Chaux-de-Fonds in Swit- zerland. (Collection Ute Dorr, FRPSL) 2.2 Chemical proof of the occurrence of the brown colour Red lead, or Parisian red, is an inorganic dye in which lead is present in oxidation stages II (Pb2+) and IV (Pb4+) and is bridged via oxygen (O2-). The three-dimensional structure of an elementary cell then appears as follows: In the case of lead (II, IV)-oxide, a darkening to a brown colour can arise through the building of lead sulphide as a result of the effect of hydrogen sulphide. Thus, in the case of red lead, the lead (Pb2+) in the oxidation-stage II reacts with the sulphide anions (S2-) and brown lead sulphide results. Pb2+ + S2- � PbS (brown). 3 Experimental results 3.1 X-ray fluorescence spectroscopy on red vignettes The authors arranged for a spectral-analytical examination of three samples of Orient Express vignettes using X-ray fluorescence (Energy Dispersive X-ray Fluorescence Spectroscopy (ED-XRF)) with a Fischerscope XAN-DPP. For each of the three samples, the measurements were made at three different points of the red vignette in order to achieve secured data collection. Each measurement had a timespan of 90–100 seconds. The average size of the measured area was 1 mm. Fig. 1b (left): Diagram of the experimental procedure and use of samples (Orient Express vignettes) during the measurement. Fig. 2 (above): Three-dimensional structure of red lead (lead (II, IV)-oxide or Parisian red) – oxygen in red, lead in grey. Source: Open- source, https://commons.wikimedia.org/w/ index.php?curid=2171936 Fig. 3a: Red Ori- ent Express vignet- te. (Collection Ute Dorr, FRPSL) Fig. 3b: Registered letter dated 6 July 1896 from Constantinople to Berne in Switzerland. (Collection Ute Dorr, FRPSL) Sample A Sample B Sample C