You can also use one of your jnats to slurry another jnat. Many nagura are just small pieces of jnat after all. See what it does.
I dont use diamond plates to raise slurry, since one loose diamond can mess up a lot of work.
Thanks. As far as I know they started to stamp their blades with cutlers to HIS majesty from 1901. I think the G in the crown might refer to George V, which would put it between 1910-1936.