Thread: Rust Problem with Renewed Bare Metal

Lately I have been lapping some old hand planes to flatten them. A few had some significant rust and pitting which I treated with Evaporust and then lapped the bottoms flat and to bear metal. While the rust and pitting appears to be gone, you can see still see “shadow marks” where the rust was. (I suppose the shadows could be rust deep in the metal) In just a few hours these shadow areas darken and become unsightly. What can I do to stop this from happening. I have tried several rust preventative materials which slow the return of discoloration but want stop it from happening. I want to end up with a “clean” unspotted/unmarred look of the freshly lapped surfaces allowing the surface to darken and develop an even patina over time. I don’t want to apply a coating that would create a clear paint like surface. I am looking for something that will soak into the metal, neutralize whatever the discoloration is, and then protect the metal from further rust. I don’t want to go to something like bluing. Any suggestions. Do I just need to lap until the discoloration is absolutely gone? We are talking some serious lapping if that is the case and I don’t want to sacrifice any more metal than necessary. Thanks

mwebster51
Welcome to our forum,
While we are a metalworking forum there are some guys better placed on the sister forum.
HAND TOOLS - UNPOWERED .

We are more inclined to engineering metalwork in this forum but there may well be someone who has an answer for you.

Derek Cohen is the person I was thinking of as he builds his own woodworking edged tools.I haven't been over there for a long time, but it might be an alternate if our guys can't help.

For my own plane irons, I am inclined to a wax bases coating but this might affect the timber being planed,so it is wiped off and re applied after each use.

Grahame

Thanks Grahame, I have communicated with Derek on a different forum in the past, he is indeed very knowledgeable. I will check out your Hand Tools Unpowered. Thanks.
Mark

My understanding of these patches is that it is cause by rust just starting to attack the crystalline boundaries of the metal under the rust. When you use a rust removes it removes the rust but leave very slightly etched grains that can still be very smooth on a macroscopic scale but show up as a different colour because they reflect less light. If this is the case, then no additive will rebuild the structure back to its original form - basically the item needs to be melted and recast. Or you have to lap it out.

It seems that this is the case, thanks BobL. Apparently these slightly etched grains are susceptible to rusting more quickly than the surrounding metal. Would that make sense? Because this appears to be what is happening.
Mark

It might be worth using electrolysis to remove the etched in rust, follow up with sulphamic acid, them neutralise with an alkaline agent (washing soda),

I've used this to remove ingrain rust staining and it seems to work quite well after wire buffing.

Originally Posted by nearnexus

It might be worth using electrolysis to remove the etched in rust, follow up with sulphamic acid, them neutralise with an alkaline agent (washing soda),

I've used this to remove ingrain rust staining and it seems to work quite well after wire buffing.

Thanks Nearnexus, I think ingrain rust must be what is there thanks!

Hi Mwebster51,

Welcome to the forum.
I've had some success with Acetic acid (White Vinegar) removing rust stains from cast iron machined surfaces. Afterwards I wipe the surface with an oily cloth, this seems to work well if the staining isn't too dark.

Thank you for the response BaronJ!
Mark