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While running this board of African mahogany through the thickness sander these dark spots appeared. They don't seem to want to go away with more passes through the sander. I wiped on some water to see how the spots might look under finish and they are even more noticeable. Has anyone experienced this and is there anything I can do to make the spots go away?

I have no idea really, but that won't stop me from stabbing in the dark. They almost look like drips and smudges of some containment. I once, without thinking, rubbed some mineral oil on part of my bench-top to make it look nice. Then a few days later, I set a pack plate down on it. The next time I went down to the shop it had soaked up the oil from the bench-top. It looked similar to those spots and it has soaked through to the other side. After a few very liberal applications of naptha soaking the stains and letting them flash off, it was completely gone and never showed up under finish.

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Bryan Bear PMoMC

Take care of your feet, and your feet will take care of you.

It came out of the drum sander with those spots? I've seen color spots in wood before but that certainly looks more like some oil dripped on it and soaked in.

Is that one of the boards you straightened up on the jointer? Is the other side that way or is it just localized to that one area? Have you checked to see what it looks like with Naptha on it?

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Steve Smith
"Music is what feelings sound like"

Yes I thought they were oil stains as well but I can't imagine any scenario where oil would have dripped on it in my shop. The spots didn't show up until I hit it on the sander but they would have been hard to see in rough cut form so possibly some oil got on it at the lumber yard. Thanks Bryan for the tip, totally didn't think about naptha (what can you NOT do with naptha!).

Yep Steve that's one I trued up on your jointer. Spots just on one side but they seem to go deep as they aren't coming off after several passes on the sander. Totally spaced and didn't think about putting naptha on it. Ill give that a try.

It looks like oil contamination, but I've seen random spots kind of like that before that were simply marks in the wood. You could try cleaning it with some naptha, which should at least reduce them if the are oil.

If nothing happens, they could be some random mineral staining, in which case you could try oxalic acid to clear them. This works well for many stains.

IIRC the boards were only on the table saw and the jointer. I'm really picky about were oil, silicone and stuff like that go in the shop so not likely from that. There was a lot of finish stuff on the bench but that would have just contaminated the surface. I have seen weird spots before in wood like that but not in a pattern that looks so much like they were splashed.

I thought about looking at it with the Naptha only because it would be a solvent for the oil as opposed to the water so it might give you a hint as to the nature of the stain.

BTW - got tickets to the Square Room on St Pats day

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Steve Smith
"Music is what feelings sound like"

Thanks Greg B, Ill give oxalic acid a try if necessary.

Yeah Steve I didn't think those stains would have come from your shop.

Great! Glad you are coming to the Square ROom show. It's always a good time.

Assuming its oil or grease I'd use K2R spray to suck out the stain. Goes on wet dries into a white powder that you vacuum off.

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Ken Cierp

http://www.kennethmichaelguitars.com/