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Black stains after stripping oak table - any suggestions?

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TCR

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I have been stripping a 50 year old oak table - See the photos.

30 years ago it was re-varnished with very dark black polyurathane varnish.

I stripped with water based varnish stripper which I have used lots of time before. The top has stripped really well, but the legs (all 6 of them!) have a residual dark staining which you can see in the photos.

Any ideas as to how to get rid of these stains before re-finishing?

- sanding isn't practical because the legs are round and it would probably take forever by hand.

- I tried Wood Bleach but hasn't touched them.

- Could it be tannin - I will try Oxalic Acid crystals- but is it likely to be tannin?

Also, the dark patches look much worse when the legs are wet (as you can see in one of the legs which is still wet from the re-applied wood bleach), so I am assuming when we re-finish the table they will be dark too when the oil or varnish is applied.

We want a rich but light oak finish but nothing like the dark brown/black it was before - any suggestions on what finish to use?

The legs are a pain, because the top is stripping really well.

Thanks, Tim
 

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gog64

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More experienced people will be along soon, but in the meantime my 2p worth. That doesn’t look like tannin staining to me. It looks like the dye in the varnish has leached through the wood underneath. FYIW I think it looks great! I’ve been working with some “exotic” woods recently (not my usual thing) and it looks very similar to a very expensive wood I’ve been turning! If I’m right, now that the dye is exposed to UV you should see it fade fairly quickly. 12 month in a sunny spot might sort it out 😀
 

baldkev

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I agree with the dye comments....
If it were bacteria in the grain or weathering it could be taken out using oxalic acid. You could try that, but if its dye, which i agree it most likely is, oxalic will have no effect. The other thing which can work to revive timber colour is hydrogen peroxide.... you can buy 9% peroxide in boots etc very cheaply. Again, i wouldn't expect any difference with this
 

baldkev

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Actually..... just thinking..... as said above, it does look cool, so how about doing a test on an inconspicuous area? I would get a couple of the osmo oil tester packets, maybe white tint and honey tint.... you might be amazed how it comes up
 

Argus

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A while back the reverse effect picked out in white - 'Limed Oak' - was all the rage.

We don't seem to see a lot of it about now........
 

TCR

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I agree with the dye comments....
If it were bacteria in the grain or weathering it could be taken out using oxalic acid. You could try that, but if its dye, which i agree it most likely is, oxalic will have no effect. The other thing which can work to revive timber colour is hydrogen peroxide.... you can buy 9% peroxide in boots etc very cheaply. Again, i wouldn't expect any difference with this
Thanks for the reply. baldkev. I have ordered some of the Oxalic acic crystals and will give it a try. In the meantime I have some 9% hydrogen peroxide and I will try that too.
 

TCR

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More experienced people will be along soon, but in the meantime my 2p worth. That doesn’t look like tannin staining to me. It looks like the dye in the varnish has leached through the wood underneath. FYIW I think it looks great! I’ve been working with some “exotic” woods recently (not my usual thing) and it looks very similar to a very expensive wood I’ve been turning! If I’m right, now that the dye is exposed to UV you should see it fade fairly quickly. 12 month in a sunny spot might sort it out 😀
Thanks gog64, sadly we are aiming for the legs to look like the top so embracing the dark patches would be a very last resort. My gut feeling is that it is the dye but I will try the oxalic acid and also hydrogen peroxide and see what happens. 12 months in a sunny spot would be wishful thinking with the UK weather!
 

baldkev

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Ok, oxalic needs warm to hot water for the best results. Leave it 10 mins and then rinse or wipe with fresh water to neutralise the acid. Best to wipe peroxide with water too, probably a similar 10 minute gap
 

TCR

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Ok, oxalic needs warm to hot water for the best results. Leave it 10 mins and then rinse or wipe with fresh water to neutralise the acid. Best to wipe peroxide with water too, probably a similar 10 minute gap
Great advice re. the hot water, thanks. Do you know a good ratio for crystals to water? I have heard 8 to 1, does that sound about right?
 

the great waldo

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The legs are beech. oxalic acid or rustins 2 part bleach should do the trick. You might have to do it a few times.
Cheers
Andrew
 

Illy

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I stripped a similar table. When I removed the legs the original mounting holes from the lathe were still there, so I was able to put them straight back on the lathe and re-sand whilst maintaining the original shape. Quite a quick process too.
 

TCR

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The legs are beech. oxalic acid or rustins 2 part bleach should do the trick. You might have to do it a few times.
Cheers
Andrew
Hi James, Thank you, I was thinking that the legs might not have been oak but another wood. Especially because the top and the stretchers cleaned up so perfectly. I will try the Oxalic acid when it arrives and if that doesn't work then I'll Have a go with the Rustins, that said, the Liberon wood bleach didn't touch it. Thanks again.
 

TCR

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I stripped a similar table. When I removed the legs the original mounting holes from the lathe were still there, so I was able to put them straight back on the lathe and re-sand whilst maintaining the original shape. Quite a quick process too.
Sounds a perfect solution, but sadly I don't have a lathe.
 

TCR

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Hi
When I strip pieces, I usually wipe over the entire piece with Liberon wax and polish remover
This is good to remove the last bits of stain and it also neutralises the wood. I would then pad over the area with a sanding pad
Thanks for the tip. I may try this if the Oxalic acid doesn't work.
 

Jacob

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I'm lazy so I would just go with finish to match with least trouble. An off the peg "oak" stain? Or just leave it as is? Paint? etc
 

Sgian Dubh

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I stripped with water based varnish stripper which I have used lots of time before. The top has stripped really well, but the legs (all 6 of them!) have a residual dark staining which you can see in the photos.

Any ideas as to how to get rid of these stains before re-finishing?

We want a rich but light oak finish but nothing like the dark brown/black it was before - any suggestions on what finish to use?

The legs are a pain, because the top is stripping really well.
As the great waldo pointed out the table is made of two different materials; the top is coarse textured ring porous oak and the underframe is fine textured diffuse porous beech. There are remnants of the old pigmented varnish lodged in the pores of both wood species. In the oak it is mostly apparent lodged in the distinct dark bands of the coarser and more open spring growth. In the case of the beech which has a fine grain lacking a marked distinction between spring and summer growth density and texture the remaining pigmented finish is relatively evenly spread throughout the small pores of the timber's surface.

I suspect the bleaching options suggested by others, whether you use A+B bleach or oxalic acid, or both, won't remove the black colour from both the wood species. If either or both of the bleaches work then you could follow up with a dye of your choice and refinish with varnish or similar. If, on the other hand, the bleaching strategies don't work you might consider applying different finishes to the different parts. You could, for example, paint or dye/stain plus polish the underframe one colour and finish the oak top just with a clear finish, such as an oil varnish which itself will darken the oak, but leave the dark pigmented bands of coarse spring growth.

I don't think you'll ever be able to get the underframe to closely match texturally the appearance of the oak because the two wood species have different texture (coarse and smooth or fine), but you should be able to get a close colour match by finishing both with a dark stain or dye plus polish. However, that is the look you've just removed and you want to get away from that, so maybe the two different treatments for the two wood species you're dealing with might be worth considering. Slainte.
 

baldkev

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I found, when looking, most 'wood bleaches' included the peroxide. I tested 2 kits, both were 'a and b' kits. Painting on a and then b helped a bit but notbenough, so i did patches if just a, then just b and ultimately i found that the peroxide portion worked as well on its own as with the second chemical ( i forget what it was ) so i bought a bottle of peroxide for a few quid and tested that against the a and b..... no discernable difference!! Well about 15 quid difference in price 😆
 

the great waldo

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Hi Tim
Tonally the sanded top doesn't look too far off the shade of the legs. I would first wet down the wood with some meths, and see how the shades match up. Then use some thing like a spirit based golden oak for the whole lot and then use a slightly darker shade of oak to blend the shades till legs and top match. By the way oxalic acid is pretty good for clearing dark stains unless the stains are pigmneted. You could try using a small brass wire wheel thingy in a dremel which should get you into the corners without too much damage. Try staining light at first ( you can always go darker) I think with a little colour the dark bits won't be so obvious and you may get a nice effect. Try and make sure the stains are light fast Morrells alcohol stains used to be really good (at least 30 + years ago when I used to buy from them!)
Cheers
Andrew
 

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