Junichi Ide is the blacksmith at Yosimitu Kajiya, Shimabara. Great guy to deal with and I like his knives, a good amount of Wabi Sabi but well made. Many of my customers love the premise of the "One man" knife operation.
I'm not sure but I think kataba/ni-mai are interchangeable in this situation.
Junichi-san just messaged me with this
"Warikomi can be done not only in Tansetru but also in Rikizai.
The company that makes the Rikizai is asked to determine which type of steel is to be blended and in what percentage, and then the Rikizai is made by roll rolling with large machines.
I then forge it and make my knives.
The advantage of outsourcing tansetsu is that it is less expensive than doing tansetru myself, and there are no tansetsu mistakes, so there is no loss of material"
Here's a pic from one of the steel suppliers with different forge welds that come in various stock sizes.
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