Germany used thermo-diffusion galvanizing to finish coins
During and shortly after World War I, the 5 and 10 pfennig coins were made of steel and the sherardizing or thermo-diffusion galvanizing technology was used to finish them. It is one of the practical applications of the surface protection technology, named after its inventor, British metallurgist Sherard Osborne Cowper-Coles.
It’s interesting to see how preserved these coins still look after more than 100 years.