Hi Joho,

Town mark Schoonhoven, four Lions Rampant, facing lef, in a shield.

Year letter
K for 1783
Yes, schoonhoven maker's mark
IR for; Jan Roozenburg, baptized 1-7-1732, date registered 1765 and died around /after 1806.
We know three maker's marks of Jan Roozenburg, all variations of
IR in a 'squarish' shield. Known maker of silver traveling/cutlery sets, and silver bag mounts. The year letter appears to be the
K for Schoonhoven 1783.
The Dutch dolphin mark; the 1859 duty mark for new unguaranteed objects of national origin. This mark was used on all new silver objects below legal standard of fineness,
those with non-precious metal additions, and on new heavily gold or silver plated objects, as long as the average precious metal content after melting with the base metal was at least 250/1000. It was also struck on rejected objects which had been submitted at lowest standard of fineness. In that case the maker had to choose between destruction or unguaranteed marking.
This mark was sometimes also mistakenly used on old and foreign objects. Dolphin mark used from 1859-1893 and valid from 1859 till 1953.
Best,
Peter