How to use Oxalic acid, and what about oxygenated water?

[Holly]

Thanks. If you do see any ill effects in the near future please will you try to remember to post?!

Holly

[Andy Dingley]

French polish is excessive, but a light coat of shellac is an excellent finish for them.

Very few timbers will "water stain" from water alone. It needs something else to happen. Lime (basswood) is notorious for blue/grey stains from water, but these are actually a fungal stain. Tropical plywoods develop dark brown stains, but these are pigments from the timber itself migrating to the surface. Oak won't usually do either of these, but is famously prone to tannic acid reactions, most of which involve metals. Plain water won't stain oak so easily, but just flowing through masonry or plasterwork will dissolve enough iron (from ochres) to make a difference and show the classic blue/black iron stain.

[Rob Morley]

I think he was referring to the fact that a threepenny bit was a small silver coin until the chunky 12-sided brass one was introduced in 1937.

[Tom]

No I didn't think for one moment that you were, however the relevant bit is the vinegar (acetic acid), I wonder whethrr this stops the reaction by neutralising the effect of the Oxalic acid thereby avoiding the need for massive dilution with water. Just an observation, I'm not a chemist.

But possibly not old enough to remember the silver threepenny bit which was much smaller than the brass octagonal one which came later.(Was it octagonal? I'm not sure) Good Luck Tom

[Owain]

"Holly" wrote | Andy Dingley wrote | > There are two easy sources for oxalic acid. One is "Barkeeper's | > Friend", a white powder you can find in hardware shops or | > supermakets. | I forgot yet again to mention that we are in France. I have seen you | recommend Barkeepers Friend before. It took me ages to find anything | containing oxalic acid in hardware shops and builders merchants.

Possibly Barkeeper's Friend doesn't work as well on zinc?

Owain

[Holly]

I have never used shellac and don't know what it is. What kind of finish does it give please? The main house has very old beams and joists which were sandblasted by the previous owner and this looks good so we were intending to just try to get something like the same thing. The wood treatment product shouldn't really be necessary, I was just going to use that to try to get the colours roughly the same thoughout.

Thanks for that. Most of these stains appeared when there was just rainwater coming off the roof and in through the open velux window directly onto the joists or perhaps onto temporary plywood sheets to provide a floor during building work. The plywood might have had old stone/cement dust on it I suppose because it is used regularly and, this place being an old forge, there is iron in the rock around here. A bit more came in after the plasterboard, battens and floorboards were up, so that might account for the stains there. Yet more appeared in one corner after a leak from the shower trap, but that would have been tap water which in this area might contain iron and certainly contains copper dissolved from new pipework. Thanks again Holly

[Holly]

No, sorry, I didn't think for one moment that you thought I was, hence the smiley. :-)

I wondered how that worked too. One would think that something alkaline might be better in that it would neutralise the acid. One acid must somehow have some effect on the other acid, it would be interesting to know what happens exactly. When the website is finished, the kitchen tiling done and the floor grouted I will buy the oxalic acid product, do some experiments with and without vinegar, and report back.

Definitely not old enough for that, didn't know there was a previous one, I see what you mean now. I think it had more than eight sides, I have one somewhere, will see if I can find it!

Thanks Holly

[andrewpreece]

I will try and remember: however, I would have to wait for at least a year after the initial application before deciding there was no realistic danger of the oxalic acid causing any problems to the advanced woodstain. However, I will post it as an advisory to anyone who happens to be reading at the time, if the remnant acid reacts with the protective coating :-),

Andy.

[Andy Dingley]

It's a natural resin (from the lac beetle) dissolved in alcohol. This makes it a spirit varnish, but it's about the lightest and least noticeable varnish you can get. A light coat of blonde shellac makes an invisible finish on almost any "unfinished" timber. There are different colours of it; about three common ones by successive purification through to blonde or white shellac, or a few others by dyeing it.

A good woodworking supplier (or

will sell you a bottle of Liberon's blonde shellac, ready mixed. Apply as it is, or maybe diluted 2:1 with meths. Use an artist's watercolour paintbrush with synthetic bristles (Golden Taklon bristles are the best) in a shape liek a 3/4" filbert (half oval). I buy mine at the local stationers for £3 - they don't need to be expensive ones.

I use a huge amount of shellac - I finish nearly everything with it.

[usenet]

Ah, but the 1930s threepenny bit woud be a 'silver threepenny bit' not the later twelve sided one. I can *just* rememeber finding the occasional silver threepenny bit in change in my distant youth.