1902, King Edward VII, 1d black ECKERLIN PROOF printed in 1924 (according to manuscript notes on other examples) on ungummed WATERMARKED PAPER as sample for selling Dr. Eckerlin's rotary press process for intaglio printing (developed by Herbst & Illig in Germany) to the British Post. Very fine. A RARE ESSAY. Photocopy of RPS CERTIFICATE (2018) for similar item of same origin included.