Job to say Rob. Could just predate the Great Exhibition, but by less than a decade if the info re: Mary is correct (she appears in the 1849 directory alongside Richards name: Richard is listed as cutler and surgical instrument maker, and Mary is listed as 'Salt, Mary & Son' cutlers and surgical instrument makers).

The design endured for a long period of time, so it could have been a decade after the Exhibition too, I suppose.

Regards,
Neil