There have been some interesting posts on this. Seems like lots of opinions on whether or not Mag Particle inspection would be of any value for inspection of damascus. Marc has some good input based on real experience. Good stuff.

I'm not a NDT tech but have been around it all my 30 yrs in aerospace. My take on Mag Particle inspection is that Fluorescent Mag Particle should be used for this application since is has the capability to resolve small flaws much more readily. This method has the superfine magnetic reactive dust suspended in an oil solution. The oil solution is flushed over the part and then the part is energized and a black light is used to reveal the accumulation of the particles where they collect.

I haven't done this on a damascus barrel but the late Dr Oscar Gaddy related to me that he did indeed use Fluorescent Mag Particle on a set and said the damascus pattern is a very dim background in the visual inspection and that a crack did indeed reveal itself. So, I have only one actual example of someone having done an crack inspection with FMP. But, it was a trusted source.