A database of stamp engravers all over the world and their work.
H. G. Schilling is listed in some catalogues as the engraver but this is wrong. All four from 1850 were designed and engraved by F. Edouard Eichens in Berlin. Gibbons only gives him as the designer. In 1856, when a 4 pfennig stamp was needed as well, Schilling was engaged to produce it but he still used the vignette portrait from Eichens, so he only engraved the new frame. The lowest value in the set became Prussia No 1 in catalogues though it was issued six years after the first stamp.
Exactly. You're a fountain of knowledge, John!:-)