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 the 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 evenly 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.