black marks on oak
- Thread starter hucks
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chrisrosenb
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A combination of uncoated metal & moisture will cause oak to turn black.
The way to avoid this is to not let the uncoated metal touch the oak.
Wax paper works well.
The way to avoid this is to not let the uncoated metal touch the oak.
Wax paper works well.
jonny round boy
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As JD2720 says, it's contact between moisture in the glue and metal - most likely from the clamps you've used, but could be metal particles from somewhere else. It reacts with the tannins in the oak & turns it black. The marks will usually sand out, unless it's veneered board & there isn't enough thickness.
hucks
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managed to sand out so no pics I'm afraid....... pretty sure there was no metal about as all the clamps were well away from the surfaces on wooden blocks. I think generally I want to devise a way to keep any water away from any parts that are on show, not only because of the spot potential but also because the damp blows the the grain a little & spoils the pre sanded timber. It's always a pain sanding back into tight spaces after glue up..........have attached pic of test fit. It's a console with walnut legs, oak aprons & a steamed beech top with a wave through inlay. Turned out pretty well apart from the beech being way too pink & looking pretty awful against the other timbers...... should have gone with un-steamed but the timber yard didnt have any........ you live and learn [unsure]
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Jesse Cloud
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Many years ago I attended a demo by Franz Klaus. I vaguely remember him saying that if you need to wipe oak with a damp cloth, be sure to use distilled water. Had something to do with the tannins in the oak reacting with something in the water which created black stains. It would be interesting if you could do a test on scrap if you have any left. Sorry my memory isn't better on the specifics.
alasdair.easton
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Hi there. Yes, if I ever wipe a damp cloth on oak I get the same thing.
I agree with some of the posters here already: it's the tannins in the oak reacting with ferrous metallic particles. The reaction is brought about by the presence of water. It's the same process that causes oak to go dark (and almost black over the centuries), and the same one that causes a black circle if you leave a metallic (ferrous) pan on a wet oak surface.
I've wondered a few times about where the metal comes from for these black dots though. My guess is that it's either particles present in the water itself or it's particles in the workshop. That second one seems the most likely to me. Do you ever use steel wool? That stuff breaks into tiny, tiny pieces that will probably float about somewhere in the shop for ever more. I've moved over to using those plastic abrasive pads to try to minimise the amount of steel wool I use. Perhaps the same problem could come from microscopic steel flakes created during sharpening.
As for how to deal with it during glue-ups, you just can't use the wet cloth method to remove glue. Bummer, I know. Try some other measures, e.g:
- masking off the joints so that squeeze out goes on to the tape rather than the wood.
- wax the surfaces you want to protect before glue up. The glue won't stick to the wax. Here's how... Put the joint together dry, clamp it, rub finish wax all around the joint, take it apart and glue up, then when the glue dries the squeeze out will just flake off the waxed surfaces. You can remove the wax if required using white spirit before moving on to whatever finish you choose (just check for compatibility beforehand).
- use less glue so the squeeze out is less of a problem (or no problem at all). I struggle with this one
- or wait till the squeeze out is nearly dry and use a combination of card scrapers, chisels, etc. to remove it. It's a bit fiddly but sometimes it's required, as we no doubt all know
I'm sure there are other solutions though. I'd love to hear them too.
Cheers,
Ali.
I agree with some of the posters here already: it's the tannins in the oak reacting with ferrous metallic particles. The reaction is brought about by the presence of water. It's the same process that causes oak to go dark (and almost black over the centuries), and the same one that causes a black circle if you leave a metallic (ferrous) pan on a wet oak surface.
I've wondered a few times about where the metal comes from for these black dots though. My guess is that it's either particles present in the water itself or it's particles in the workshop. That second one seems the most likely to me. Do you ever use steel wool? That stuff breaks into tiny, tiny pieces that will probably float about somewhere in the shop for ever more. I've moved over to using those plastic abrasive pads to try to minimise the amount of steel wool I use. Perhaps the same problem could come from microscopic steel flakes created during sharpening.
As for how to deal with it during glue-ups, you just can't use the wet cloth method to remove glue. Bummer, I know. Try some other measures, e.g:
- masking off the joints so that squeeze out goes on to the tape rather than the wood.
- wax the surfaces you want to protect before glue up. The glue won't stick to the wax. Here's how... Put the joint together dry, clamp it, rub finish wax all around the joint, take it apart and glue up, then when the glue dries the squeeze out will just flake off the waxed surfaces. You can remove the wax if required using white spirit before moving on to whatever finish you choose (just check for compatibility beforehand).
- use less glue so the squeeze out is less of a problem (or no problem at all). I struggle with this one
- or wait till the squeeze out is nearly dry and use a combination of card scrapers, chisels, etc. to remove it. It's a bit fiddly but sometimes it's required, as we no doubt all know
I'm sure there are other solutions though. I'd love to hear them too.
Cheers,
Ali.
