Andy, another great thread on sympathetically restoring a lovely tool. As always a pleasure to read and learn. (I've already stolen your restorative recipe). Got to thinking about the blackening process. Realised I knew not much about anything but I do have a friend who knows lots about lots of stuff.. Skyped him so i'm gonna copy and paste bits of the conversation in the hope it helps. You'll have to piece together the rest of the conversation. Shouldn't be hard its me Just going 'oh'/ 'really?'/ well I never' in the missing bits. The usual then.
Maybe this will help. I'm not qualified to judge.... It might be a bit awkward to read in redacted form!
Part 1:
[19:41:06] D: just warm it and then apply the oil
I get things much hotter in the forge and get a similar effect
but the electrolysis process also chemically changes the residual iron oxide to the black form - like magnetite I think
easy to do with a bucket, car battery charger some washing soda for the electrolyte and some sacrificial steel rods
[19:43:00] C any particular oil?
[19:43:18] D I tend to use beeswax or veg oil
you can use old motor oil but that is not good for you
P2:
[19:45:14] D reading page 2, washing soda is the best...not as agresssive as the vinegar and table salt
but make sure it's washing soda
P3:
[19:46:07] D: the other kind is good for other things
I have done the electrolysis thing...it does work
and you can make up containers for odd shapes
Also worth looking at is the tannin method...very strong tea solution
[19:47:29] Chris : shut up <<<< SEE!
[19:47:31] D: didn't work in my experiment but a chemist was saying it is the mutts
[19:47:53] D: but I would go electrolysis
[19:48:06] D: just make sure you get the polarity right
[19:48:18] D: takes a few hours
Maybe this will help? Some leads? Hope it helps.
Cheers
Chris.