I've just been refurbishing a box of assorted spokeshaves - and best of all I've finally got a Preston quirk router !
One thing I noticed is that japanning falls off when you leave it in the electrolysis tank. Now this isn't news, but there was a very obvious variation between US Stanley japanning, that barely shifted unless already damaged, English Stanley japan that came off readily in big sheets and Preston's japan that turned to mush almost instantly.
That set me thinking - _Why_ does japan come off ? I wouldn't expect it to be affected by the current and my tank electrolyte is cold and has a fairly neutral pH. The only reason I could think of is that the English Stanley japan is permeable and there's some electrolytic effect happening underneath it that destroys the adhesion. US japan doesn't appear to detach unless the underlying iron is already rusting, and then only by lifting around the edges. Presumably Connecticut japan is itself impermeable.
Any thoughts ? Anyone know the various recipes used and if they did vary like this? I'd have thought all these japans had a pretty high bitumen content and that makes a fair electrolytic etch resist on its own.
PS - A "quirk router" is spokeshave look-alike that cuts narrow, deep grooves. The cutter is a double sided affair, made from a strip of thin sheet. The business end looks like a C shape, one side cutting the sides of the groove and the other ploughing the bottom - like a tiny plough plane with twin nickers. Sharpening is an interesting exercise with a tiny diamond hone!