When dealing with stones that have no ink stamps it is nice to have some reference points to go back to. I am lucky enough have a few Nakayama that are ink stamped “Maruka” that date back to the first half of the 20th century, and here is an example how one stone can act as a sort of a Rosetta stone.
In both stones you can find similar indicators besides the color that in this case matches up pretty well. The circular “kan” pattern found in some chu-ishi-naori deposites, the typical Nakayama “kawa” or skin that displays rust colors along with deep black, and there is a specific sparkle in the sheen that actually reflects light like a prisim. The overall fineness of the stone should match up as a finishing stone. Also some Nakayama have these linear “Namazu” lines that are filled with a ligher color softer mineral.
Of course not all Nakayama stones are neither fine nor fast, and these qualities can only be determied by using them. The stones with the Maruka ink stamp that are genuine tend to have special attributes however because as a rule Kata-san, the previous owner of the mine, was stingy with his grading and stamped only a small percentage with this now famous inked signature. Smaller, chipped, cracked or inferior stones basically just went to the different wholesaler with no inked markings. I know of no other miner from the era who ink stamped the stone with the mines actual name, the wholesales had the ink stamps and they used them liberally. It appears in looking back that Kata was the only miner of that era who used an ink stamp as his sign of approval or endorsement, and funny enough this stamp refered to as the Maruka stamp does not even mention the proper name of the mine. Alx