wood bleach

[madge]

Just wondering if anyone can recommend a suitable product for bleaching wood (wenge)?

 

[matthewwh]

Oxalic acid is the usual choice, drop me a pm if you need a bit.

 

[mrpercysnodgrass]

It depends on how light you want to go, Oxalic is a fairly mild bleach, if you need to go lighter then you will need Hydrogen Peroxide.

http://www.agwoodcare.co.uk/Item/fiddes_bleach_set

 

[Eric The Viking]

I recently got about 250ml of peroxide from our local independent chemist. They had it in a range of strengths, and the strongest worked very well cleaning a burned enamel saucepan!

. We were on good terms with our nearest chemist in our previous place; he had an account with a lab chemicals supplier and could get most things, as long as I had a good enough excuse - for some reason merely wanting to poison the neighbours didn't cut it.

Worth a try, possibly,
E.

 

[marcus]

Oxalic is great for removing certain types of stains but won't significantly lighten the wood. If that is what you want to do you really need a 2 part A/B bleach like this:

Part A

http://www.jpennyltd.co.uk/shopping/pgm-more_information.php?id=159

part B

http://www.jpennyltd.co.uk/shopping/pgm-more_information.php?id=160

Part A is sodium hydroxide (lye), which actually darkens the wood, then part B (hydrogen peroxide) removes the colour. Used in combination you get a much greater effect than hydrogen peroxide on its own.

Be careful, it's very caustic and nasty so you need to wear proper protective gear.

 

[madge]

Thanks all for the fantastic response. Mathew that's a very generous offer but I'm looking to go as light as possible so maybe the a and b system is the way to go. I've heard that if you bleach wenge, the darker woof remains dark and only the lighter wood is bleached. Has anyone tried this?

 

[marcus]

Has anyone tried this?

I haven't tried it, I suggest you do lots of test pieces on scraps (eg leaving the bleach on for different lengths of time, try both the B on its own, and the A followed by the B etc) until you find a technique that gets the result you want. If you are trying to make the whole thing go light this should be achievable with A and B I'm sure.

By the way, you don't get the full colour change effect until the wood has completely dried, it often ends up much lighter than you think it will when it is still drying. Also you can repeat the process a couple of times if it is not light enough (any more than that and you may start to damage the wood....)

Once you have the colour you want you need to neutralise it by washing the timber with vinegar or mild acetic acid solution. And obviously make sure raise the grain and sand back before bleaching!

 

[custard]

Thanks all for the fantastic response. Mathew that's a very generous offer but I'm looking to go as light as possible so maybe the a and b system is the way to go. I've heard that if you bleach wenge, the darker woof remains dark and only the lighter wood is bleached. Has anyone tried this?

I haven't bleached wenge, but I've used A&B two part bleaches a fair bit with oak and other paler woods and there's a couple of things you should think about. If after bleaching you want to avoid a yellow or orange cast then you might want to consider acrylic finishes, and if you do plan on acrylic finishes then you musn't neutralise the bleach with vinegar, just a couple of washes with water.

 

[marcus]

and if you do plan on acrylic finishes then you musn't neutralise the bleach with vinegar, just a couple of washes with water.

I didn't know that! What happens if you do?

 

[custard]

and if you do plan on acrylic finishes then you musn't neutralise the bleach with vinegar, just a couple of washes with water.

I didn't know that! What happens if you do?

I was told that it can cause poly/acrylic finishes to bubble or flake, and recently I was using some Rustins A+B bleach and sure enough they were specific in their instructions about neutralising with water if using water based acrylic finishes. I've been using this process for some time, at least seven or eight years, as I like that bleached out "driftwood" look without any of the yellow/orange tint that you always get with oil or varnish finishes on pale woods, and I've had no problems following the neutralise with water guidelines.

 

[Bretonfox]

Oxalic is great for removing certain types of stains but won't significantly lighten the wood. If that is what you want to do you really need a 2 part A/B bleach like this:

Part A

http://www.jpennyltd.co.uk/shopping/pgm-more_information.php?id=159

part B

http://www.jpennyltd.co.uk/shopping/pgm-more_information.php?id=160

Part A is sodium hydroxide (lye), which actually darkens the wood, then part B (hydrogen peroxide) removes the colour. Used in combination you get a much greater effect than hydrogen peroxide on its own.

Be careful, it's very caustic and nasty so you need to wear proper protective gear.

Hi Marcus, sorry for reviving this old thread but I'm wanting to bleach green poplar white and stumbled across J Penny's A/B bleach. However they are selling as part A a sodium silicate solution. As you say, and I've researched, it is sodium hydroxide that is recommended. Do you know if sodium silicate contains sodium hydroxide?

Cheers

 

[Peter Sefton]

We have oxalic acid for mild bleaching or black stain removal, A B bleach is much strong but my favourite bleach is Lakeone but I have not tried it on wenge.

https://www.agwoodcare.co.uk/products/l ... dwhitener/

Cheers

Peter

 

[Eric The Viking]

Sodium hydroxide is available inexpensively over-the-counter in your local ironmongers' shop as "caustic soda", used mainly for drain cleaning.

I recently tried to get hydrogen peroxide from Boots, but they only keep it in very small bottles for medicinal purposes (cleaning/disinfecting wounds, NOT drinking!), or, with unwanted additives, as hair bleach. This is frustrating, as it's generally nicer to use than the chlorine bleach you buy in the supermarket. Apparently you can get larger quantities and higher concentrations from specialist suppliers.

Both peroxide and NaOH (sodium hydroxide) are nasty, but on balance (and it's a tough call), caustic soda is probably nastiest of all. Wear eye protection, long rubber gloves (i.e. must be waterproof) and a good apron if you don't want holes in clothes (or worse, chemical burns).

And always add crystals to water to dissolve, never the other way round (wrong way means it spits back!).

Don't ever mix the two, either directly or by treating wood with the second one without washing the wood very well first with water. The direct reaction between them is likely to be rather "energetic" (not in a good way).

Aside: if you know anybody who works in rocketry, that might be handy: HTP ("High-Test Peroxide") is the oxidiser in many propulsion systems, including the Nammo rockets in the Bloodhound car, and quite a lot of the current crop of space launch vehicles. HTP is very concentrated peroxide and extremely nasty stuff to handle. You could probably bleach half a forest with the contents of Bloodhound's oxidiser tank!

There's at least one chemist on this forum, so I'm happy to be corrected...

E.

 

[Phil Pascoe]

... over-the-counter in your local ironmongers' shop ...


hahahhahahahahahahahaha ...

 

[whiskywill]

And always add crystals to water to dissolve, never the other way round (wrong way means it spits back!).

And never in that old aluminium saucepan you kept for such a purpose. The caustic soda eats the aluminium and produces Hydrogen gas.

 

[whiskywill]

I recently tried to get hydrogen peroxide from Boots, Apparently you can get larger quantities and higher concentrations from specialist suppliers.

Readily available on eBay.

 

[AndyT]

... over-the-counter in your local ironmongers' shop ...


hahahhahahahahahahahaha ...

Well, if you choose to live in a county where the only shop is Trago Mills, you've only yourself to blame!

Are we really that unusual in Bristol? There are two long established proper ironmongers within ten minutes of me (free advice, screws counted out while you wait, timber cut to size, etc) and I can think of several more nearer Eric, one of which has been trading since 1850. On the other hand, several branches of B&Q have closed in the last few years and are probably not much missed.