The master mark script JK has been attributed to Jan Kamphuis. He worked in Zwartsluis, but had his work tested in Meppel. The attribution is based on the master mark JTC that belonged to his son Jan Thomas Camphuis. There was no known silversmith in Meppel with the master mark JK, so it has been assumed that this mark belongs to a silversmith from outside Meppel. Given the relationship with his son, the master mark JK has been attributed to Jan Kamphuis from Zwartsluis. See also: J. Timmer "350 Zilverstad Meppel", page 111. Date letters were not introduced in Meppel until 1765. Jan Kamphuis silversmith in Zwartsluis around third quarter eighteenth century. Had his work inspected in Meppel. His son Jan Thomas Camphuys silversmith in Zwartsluis had his work inspected in Steenwijk from 1807.
Jan and his son both use an extra/device mark; a kind of house with a serrated contour on the top.