Gustav, I have now had the opportunity to examine perhaps the best screen photograph that is available of the Sendai keris. I have Photoshopped this image and reworked it to the limit of my capability, I have viewed the results on a high resolution screen, and then examined the screen image with a good quality magnifying glass; my eyes test at 20/20 wearing reading glasses.
In the sorsoran area of the Sendai Keris I can see some very faint, very slight white marks; in my opinion these marks, or traces, could be due to a number of reasons. I most definitely cannot see anything that would permit me to state categorically that the Sendai Keris has pamor miring.
Here is a link to the article by Wahyono Martokrido that you posted on 21st September 2012.
What Wahyono Martokrido says about the pamor in this keris is:-
The pamor is light grey in color, showing the patterns of curvy lines. The color of the pamor is not so contrast to that of the iron. This pamor can be categorized as pamor sanak, i.e. pamor made of different iron with so small difference in grain size and phosphorous (and arsenic) content in the metal.
( the reference "13" is to Prof. Piaskowski's 1995 paper, a paper in which I had some involvement)
I think we might have to agree to disagree on this matter relating to the Sendai Keris Gustav, I can see no evidence of pamor miring, Martokrido could see only pamor sanak, and he held the thing in his hands.
I will accept that you can see firm evidence of pamor miring, but I cannot.
However, Martokrido does mention "---patterns of curvy lines---"; this indicates clearly that the pamor material has been folded and worked, but it cannot be taken as evidence that this working involved the miring technique.
Personally, I do not find the appearance of this twist pamor in Moro metal work to be so puzzling. Clearly it came from outside the area and was not an indigenous development.
There was solid, continuing trade and cultural contact between virtually all areas of Maritime SE Asia during the time in which this twist pamor in Moro weapons made its appearance; the most advanced smiths in the region during this period were those from Jawa/Madura (in this context Jawa and Madura can be considered as a single entity, the variation between the two places can be likened more to a district variation rather than anything else).
The style and execution of the pamor in the blade under discussion here, as well as other blades of this type that I personally have seen does appear to be Madurese. To my mind, this indicates a high probability that this pamor is a direct product of, or is linked to a smith, or smiths from Jawa/Madura, most likely Madura.
There is a possibility that the link for this pamor could be to some other place, and some cultural root. However, in light of the available evidence of trade and cultural contact across Maritime SE Asia, I do feel that a link to anywhere other than Jawa/Madura must be regarded as an outside possibility, rather than a probability.
I do feel that we are both on the same track here, but I think we must agree to disagree in respect of the nature of the pamor in the Sendai keris.