FEPA News

FEPA NEWS 45 49 Developments in Philately The following illustration is a compilation of the X-ray fluorescence spectra of samples A, B and C. The energetic transitions are given in keV (= kiloelectronvolts). The red arrows mark the transitions for the lead in red lead dye. At the extreme left of the spectrum is the lowest energy transition – the so-called K�-transition of the lead (2.4 keV). Further transitions for the lead in red lead, at higher radiation intensity, at 10.5 and ca. 12.6 keV are clearly shifted to the right in the spectrum. One further recognises the elements potassium, calcium, iron, copper, bromine and strontium in the samples. Calcium, for example, suggests calcium sulphate, which is often used as a filler in paper. (Left) Fig. 5b: Magnification of the lower part of a glass beaker with the strips from a red Orient Express vignette. 3.2 Chemical proof of the formation of the brown colour Some of the authors (Uwe Diehlmann, Stefanie Clade, Dr. rer. nat. Stefan Marx) carried out this proof with a part of a red Orient Express vignette in a chemical laboratory. First, 6g of thioacetamide was dissolved in 60ml of distilled water at a temperature of 70–75 C� under constant stirring. After a clear solution was achieved, a strip from a red Orient Express was placed in the solution. Then 5 ml of 5% hydrochloric acid was added in portions/drops to the aqueous thioacetamide solution, whereby hydrogen sulphide was released (in-situ) in the solution. The created hydrogen sulphide gradually reacted chemically with the Pb2+ cations present, causing a clear colour change of the vignette. Fig. 4: X-ray fluorescence spectra in the three samples (Sample A: ____; Sample B: ____; Sample C: ____) (Left): Fig. 5a. Set-up of the experi- ment in a chemical laboratory. The bottle at the right and the glass in front contain the thioacetamide, which, in an aqueous solution, releases hydrogen sulphide when hydrochloric acid is added.