oxalic acid

[roger]

For those of you who need to source Oxalic acid. Beekeepers use it for varoa control. Try a local search or Thornes is the national supplier. http://www.thorne.co.uk/

I dont know how it compares on price.

Roger

[Nessa]

Gosh, I was just about to ask about this. what is the method for using it as a stain remover a) on a boat, b) on a wooden window sill?

[Ancient Geek]

Stain remover? Well.
Just remember it is a bleach, - that's what you are doing bleaching.
You'll likelt replace a dark discolouration with a very light one unless:-
Over the years I have seen a number of wooden boats badly stained renovated to look like new, all the succesful ones were taken back to the bare surface Care neccesarry if its ply - veneerrs are thin!), all over not just locally the stains bleached and the whole surface stained maybe with a light stain like cold tea (A Bob Hoare favourite.) or any water based stain light being better and then finished as you would any new surface using the treatment of your choice, from Copal Varnish to Epoxy and all the gubbins.
There is no satisfactory short cut no satisfactory quick way even to Artful Bodgers, do it once do it right it'll save time in the long run.
By the way a very good way to get varnish off and down to bare wood is to hire a blaster and using crumbled walnut shells 9instead of sand you can do the inside of a Dragon in a morning!

[Rupert]

How many walnuts do you eat? Do pistacio shells work?!

[Nigel]

Health & Safety rules require a notice on the blaster saying:

"Warning - May contain nuts"

Maybe we also need one on the front page of this forum

[Ancient Geek]

I am perfectly serious.

[Nigel]

Hi AG,

I do have a vague recollection of crushed walnut shells being used in a proprietry hand cleaner. I think Rupert was asking where one sources them in that sort of quantity? buying the whole walnuts would seem rather wasteful and time consuming.

Going back to being silly, I presume one has to be careful using them because of the adage "your walnuts hurt the one you love............"

[Rupert]

I was indeed wondering where you got walnut shells from by the truckload.

[Ancient Geek]

The cleaner hirers will let you have them.
Walnut shells crushed, seem to love me tender!

[Nigel]

Until that post I did not realise Elvis was singing about yachting. If he loved his tender, how did he feel about his big boat?

I will wager a pint that Dr. B posts a whole version of the lyrics before bedtime.

[chris]

There is a lot on oxalic acid in old forum posts to be found But briefly...

Oxalic acid is unique because it removes a specific type of stain where certain things such as iron react with the tannic acid in timber. Moisture, particularly when it contains traces of iron, react with the tannic acid to make a black stain. Oxalic will deal with this and the greying effect of weather ONLY. It does not lighten the timber itself but will have the effect of restoring the original colour and even out the patchy clour of aged timber. (PS this is why you must not mix the acid powder in a metal container. Use glass jar, nylon scrubbing brush or plastic pot scourer to work it into the timber, then neutralise afterwards with a solution of one quart of water plus two heaped tablespoons of baking soda.Then wash it all away with water.).
Other bleaches for woodwork are:
Peroxide bleaches, usually you need A and B. This WILL remove colour from timber. So mahogany will turn very pale. ( However it does not touch Ebony!) This can be useful where new timber has been added to old as you can get all the timber back to an even colour and then sart from fresh (even then applying a dye stain if needed).

Chlorine bleaches
If dye-stain has been applied to timber and you want to remove it you can use a weak chlorine based laundry bleach but several applications are needed. A swimming pool bleach is stronger and probably cheaper. (calcium hypochlorite) . Again this is very useful as it will remove only the dye stain and should not affect the colour of the timber (much).

So three different bleaches but each for specific uses. needless to say they need to be applied to bare wood. Fiddes in Cardiff has Oxalic and Peroxide A and B, or you can make your own oxalic from rheubarb! Don't forget the safety precautions as most of these are lethal. (don't eat rheubarb and spinach in the same meal as that could well be too much oxalic for you).

The next step in restoring good colour to old timber is the finish you use. Traditional oils and varnishes will bring out the colour and add a lovely amber tint (so will G4), Epoxy does not and in my eyes leaves a rather deathly aneamic effect especially on pale woods.

Chris

[Ancient Geek]

Thank you Chris for this very informative analysis.

[Shanty Man]

Used to be on the poisons register and you had to go through a right old rigmarole to obtain it. Now just go to E-bay and they offer loads in powder form. Fine if you want to inherit early.
Lemon juice I used the Jif version on gelcoat and gloss paint to good effect. White vinegar is said to work too although the white version may be best. So after removing the rust stains do you fancy a pancake or fish and chips ?