If they told me, they would have to shoot me. It's tough to keep secrets from Mark
I can say this. He is a Japanese Left handed man. And it is just one man making these. Now you know far more than you do about Aritsugu, Masamoto, or many other knifemakers who source out their production to multiple knifemakers
His situation as a single knifemaker is that to give up his trade secrets is to invite competition from larger knifemakers and put him in a position where he might be working for others and not be in a position to be uncompromising in his art working for himself. It is a position I fully understand and must respect. Even the details of his Shirogami knives to extract maximum performance is a trade secret. In some of my conversations with him, it is apparent that his knowledge of heat treatment, most especially so for the more difficult black steel knives, combines a long familial knowledgebase of tradition combined with a very scientific and exacting approach to controlling the tempering process. It is his mastery of the black steel along with the steel itself that makes these knives quite special.