…or just only an item, which was made privately onboard the Thor, using any estranges materials?
Seriously, I still have doubts that every (any?) items are manufactured by any Japanese jeweler. There are enough items, who were handicraft by the sailors itself, e.g. while during on the sea (Iron Cross, etc.) or any other reason.
Especially for this unique items, there will be almost no 100% proof able comments about the manufacture or date, authenticity of fake, etc.
Just my two cents.
BR, Chris