Removing dark discolored areas

[hyperbolica]

I've got an Olds Recording that I'd like to some day refinish. But there are some heavily discolored areas around the bell rim. I've seen people put burning cigarettes on the rim of their instrument, and then it burns down to the butt and burns the bell. Thats what I think this is. Its maybe 3/4" x 1/2".x

I've tried polishing it out, and stuff like Wright's does not even touch it.

[BGuttman]

If it's a tar, you need to "strip" the tar. Try an organic stripper like Simple Green followed up by a polish.

Have you tried scraping at the stain with a knife and seeing how deep a gash you need to get underneath? If it's deep there may be no satisfactory way to remove it.

[hornbuilder]

People burn their horns with cigarettes!?!?! What!?!?

Please post photos. I have no doubt it is acid bleed.

[ithinknot]

Sounds like acid bleed

Have you tried scraping at the stain with a knife and seeing how deep a gash you need to get underneath?

Please don't

[hyperbolica]

Looking at it closely, it doesn't look like a cigarette burn, but it is stubborn. Normal polishing isn't doing anything to it. I'm reluctant to try anything more aggressive until I've got a better idea what it is. It is much darker than your average acid bleed. But its not something thickly caked on that can be mechanically scraped off. It looks black in normal light. I'm talking about two areas, one to the right and two smaller ones to the left of the flash flare.

This is a 1950s Olds, and came to me this way. I don't want to do anything drastic because it plays great. These things look great when refinished, but these spots have to go before I can do that.

IMG_20230129_124946702~2.jpg

[ithinknot]

Huh. Ok, not bleed from the bead. Bottom left is particularly odd, though maybe the photo isn't ideal - almost like something was splashed on the bell before lacquering and reacted later...?

[Doug Elliott]

Is there lacquer on the bell now? Can you tell if it's over or under the lacquer? Look with some extreme magnification. I've seen stubborn tarnish sort of like that, that's very hard and polishing just burnishes and makes it harder. It might need some fine abrasive like 1000 or 1200 grit wet sandpaper like you can get at an auto parts store, then buff.

[ithinknot]

A graduated set of Micro-Mesh cloth-backed sheets is perfect - you can sneak up on it in reverse from something like 3000 grit (won't be rough enough) and find the finest grade sufficient to get the job done. Having removed the mark, you can then go back up the grades locally, leaving the buffing wheel just to randomize the scratch pattern, not remove a meaningful amount of material. (Though buffing out straight from something like 1200 isn't exactly brutal.)

[hyperbolica]

Doug, there's little or no lacquer. It's directly on the metal. I've got some fine abrasive paper. Would Muriatic acid work?

[BGuttman]

... Would Muriatic acid work?

Muriatic acid (hydrochloric acid) is pretty aggressive. If the stain is copper oxide it will remove it but you have to be ready to swab the spot quickly with some baking soda solution as soon as the stain disappears or you will have red rot. If the stain is copper sulfide, most strong acids won't work on it (except maybe to remove it from below by dissolving the underlying brass). I saw a tarnish removal procedure using white vinegar and salt; sometimes as a paste and sometimes in boiling water. I don't know how effective that would be.

I personally think it's more likely that the abrasive technique will be the overall better solution.

[Doug Elliott]

I'm not talking about some generic "fine abrasive paper."
Use 600, 800, 1000, or 1200 wet-or-dry, and use water. It's available even finer than that, and all of those are probably available by the individual sheet at most auto supply stores. You don't need much. It's about the same range as what you can buy to refinish plastic headlight lenses that get cloudy. No coarser than 600 and I'd start with 800 or 1000. Or micro-mesh, but I'm not as familiar with it although I do have some.

When you're done, polish your headlights with it, wet.

Muriatic might work but I'm less familiar with that and I probably wouldn't go there.

[RichC]

Simichrome seems to work much more aggressively than Wrights or similar. Might be worth a try.

[Doug Elliott]

I use Simichrome occasionally too. You can probably use it for a final polish after the finest sandpaper.