Tarnished/burned plane sole?

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Forum topic by AESamuel posted 03-23-2015 03:23 PM 595 views 0 times favorited 6 replies Add to Favorites Watch
View AESamuel's profile


61 posts in 644 days

03-23-2015 03:23 PM


I’m planing some quarter-sawn oak with my stanley no.4 and cheap scrub plane and I’ve noticed both of my planes have an odd blue tarnish just behind the mouth of the plane! It definitely wasn’t there before I started this morning.

My first thought was that the metal had somehow been heated up and changed colour but I can’t imagine I was building up that much heat! I’ve been using a tea-light candle to lubricate the bottom of the soles – could this be tarnishing the plane? It would make sense because the portion of the sole just behind the mouth wouldn’t rub against the wood that much and therefore the wax could be on there for longer?

Here’s a picture. (The dark patch in front of the mouth is a reflection of my black camera)

Thanks for any insight,

6 replies so far

View TheFridge's profile


5678 posts in 908 days

#1 posted 03-23-2015 03:25 PM

Maybe a shallow spot in the sole?

-- Shooting down the walls of heartache. Bang bang. I am. The warrior.

View AESamuel's profile


61 posts in 644 days

#2 posted 03-23-2015 03:28 PM

Maybe a shallow spot in the sole?

- TheFridge

That’s what I’m thinking, it was re-ground by a professional plane maker so it wouldn’t surprise me if he left that part shallow to avoid taking too much off the sole.

I’m just curious as to what is causing the blue colour.

View chrisstef's profile


15472 posts in 2428 days

#3 posted 03-23-2015 03:28 PM

Could it be the tannins in the oak changing the color of the steel? Kind of like removing a cut nail from oak and seeing the black mark left around the old nail hole. I believe that the tannins from the oak are reacting with the steel but its just a guess on my end.

-- "there aren’t many hand tools as awe-inspiring as the #8 jointer. I mean, it just reeks of cast iron heft and hubris" - Smitty

View Ocelot's profile


1459 posts in 2060 days

#4 posted 03-23-2015 03:32 PM

I suspect the blue color is “black oxide” Fe3O4. It’s actually a good thing. It’s hard, thin, doesn’t flake off. It’s the same coating that is intentionally created when “blueing” a gun.


View unbob's profile


693 posts in 1325 days

#5 posted 03-23-2015 04:55 PM

Looks to me the plane maker did very good job grinding the sole. Not an easy task as the soles are very thin. The discolored area looks like a depression to me from the photo, but it is very shallow.
I have ground some of my smaller planes in a 6X12” surface grinder. When going over a weak spot like the blade slot, the metal will heat up and expand a little, rise up. Then, end up a shallow area….even with flooding the work with coolant.
Candle wax in my experience with soles brought to such a fine finish doesn’t work very well. I found a very small amount of paste wax better.

View Ocelot's profile


1459 posts in 2060 days

#6 posted 03-23-2015 06:15 PM

Wait a minute! I know what it is! It’s the reflection of your head! :-)

OK. Sorry. That’s just what it looks like – a reflection.

[edit: Now I see that you already said that.]


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