Calabrese,
of course the ZEN painting is not related to casting techniques!
I just referred to the idea of "unfinished". This is possibly only a different concept in our Western brains and does not necessarily correspond to Japanese aesthetics in arts.
Leaving things out can make room for thoughts and emotions, while we in the West fill in every corner of an art-work so there remains no space for your own interpretation and imagination (very generally speaking).
It is just a different way of seeing and feeling(s), I think.
In addition to that, I find it very unreasonable to believe that an 'unfinished' TSUBA was sold/released from a workshop, with clear signs of hammer-work on the SEPPA-DAI (which is a proof that it is not cast!), with mounted SEKI-GANE as a proof of use, would be embellished with a silver FUKURIN.
This part of the whole discussion is redundant in my opinion.