Coin silver master salts, Bigelow Bros & Kennard

This is a nice pair of 3 1/2" master salt spoons. They are in good condition with no dents or repairs. They are marked "Bigelow. Bros & Kennard", "Boston" and "900". This is the first time I've seen "900" from Boston. Wood & Hughes in NY used this purity mark occasionally. Ca 1850.