Electrolysis - different japans, different resistance to falling off ?

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!
--
'Ph'nglui mglw'nafh Cthulhu Evesham wagn'nagl fhtagn'

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Have you seen this site? It is a long sheet but it seems the best stuff was done by Stanley and Ford automobiles: http://www.cranialstorage.com/wood/html/japanning.html Go through the whole sheet though... real jappaning is baked on in incremental stages of tempertures, quite a task. (I have not done it myself yet)
Alex
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Andy Dingley wrote:

My understanding of it, based on what I've read on the Old Tools (The Porch Jeff) Group is, the japanning that comes free didn't/doesn't have a good bond/was compromised in the first place.
UA100
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Unisaw A100 wrote:

That'd be my guess.
There are two things going on during electro-stripping, which is what you're doing. First is that material is driven off the Anode (plus pole on the set up) into solution and from the solution onto the Cathode (minus pole). The other thing that happens is that hyrdogen bubbles generate on the Anode and Oxygen bubble are generated on the Cathode. These bubble start out very small and grow. There are twice as many bubbles formed on the Anode than on the Cathode since it's H2O that's being broken down into two Hs for every O.
On really rusted pieces, the rust can extent UNDER what appears to be a good japaned surface. The hydrogen bubble can therefore form UNDER the japaning and, as the bubbles expand, lift and remove some of the japaning.
The process is similar to something called cavitation which "eats up" ship and water pump propellers/ impellars. It's cavitation that ultrasonic cleaning uses.
I think modern powder coating has replaced japaning when very durable finishes are required.
BTW - electroplating and elecro stripping are "line of sight" If the "cathode" can't "see" the part of the "anode" you want to remove only the hyrdogen bubble will be doing the mechanical stripping. By placing the "anode" in the center of the stripping tank and several "cathodes" around it, cleaning will be improved. Cathodes shaped like the negative of the part being stripped will produce a more uniform surface finish. This is because you'll get higher current density (and more stripping) on surfaces closest to the cathode. At low current settings, this isn't a big deal. At high current settings it can noticably eat up anode surfaces closest to the cathode(s).
You can also add a little protein to the stripping solution (powdered gelatin works pretty well, though dead flies will also add protein) to increase the "throwing" effect.
If you really want to mechanically remove rust from deep pits you'll need a polarity flipper. What this does is repeatedly flip the polarity, stripping then plating the anode. The polarity flipper should have two adjustable functions - one that sets the percent of time stripping (should be greater than 50%) and the other that sets the time interval for each flip. By flipping the polarity very quickly you get a lot of very tiny bubbles forming and collapsing on and UNDER the rust, loosening and then removing it.
(I use to make jewelry and plating and stripping were just two more techniques in my knowledge and skills set)
charlie b
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