Funny being a machinist and being around Prussian blue for all these years, the thought of using it around wood never occurred to me. I hate (loathe) the stuff big time but always have it on my bench for metal fitting work especially for locks, triggers, and my bpcr rifle builds.
Never had a problem or mess using the 'ol inletting black standby, applying with q tip or small brush......it does not require much. And as noted, sooting with acetylene works great too, except for the shop air having black airborne floaters.
kw