Wood bleach - what is it really?

      How bleach works, plus developing a process to subdue alder grain and flecks. July 22, 2003

Question
What happens to wood when bleach is put on it? Why does the grain of wood lighten as well? I know that wood is made up of just a few things. Is it actually those things that are affected by the bleach? Bleach appears to bleach anything.

Forum Responses
From contributor J:
Color in an object is produced by certain chemical configurations in the individual molecules (called chromophores) reacting to light. Chromophores (from the Greek “chromo” – meaning color) are specific electronic bonding arrangements between atoms and oxidative bleaches (oxygen and chlorine based) work by disrupting this bonding in such a way that the molecules can no longer produce color. Other bleaches like oxalic acid are called reducing bleaches and actually convert the colored compound to a different, colorless one. While this concept may be difficult to understand, the important part to remember is that bleaches do not really "remove" the color of a substance, they simply change it to a slightly chemically different, colorless one.

Not all woods can be bleached. As a general rule, inorganic colors that are produced by strong, stable molecular bonds will not react to bleach. Ebony doesn't react to bleach and inorganic materials like carbon black and iron oxide pigments used in wood stains can only be completely removed by scraping or sanding the color off the surface of the wood.

2 part (A/B) bleach is an oxygen bleach and the two components are either mixed right before application or part A is flooded on, followed by part B. Once sodium hydroxide and hydrogen peroxide are mixed, a third chemical called sodium hydroperoxide is formed which is a very aggressive (chemists call aggressive “highly reactive”) compound that seeks out and destroys certain types of chromophores. The sodium hydroxide (part A) has another effect. It swells or opens up the cellular structure of the wood, making the sodium hydroperoxide work more effectively. The big advantage of this product is that it will lighten or remove the natural color of wood, and it’s about the only product that works. It was used extensively by furniture companies up until the 1980’s to blend different colored woods together as the first step in finishing, so the piece would look like it was all made from the same wood when it was done (called color conformity). However, a big downside is that the sodium hydroxide destroys the wood fibers to some degree (sodium hydroxide is the first step in pulping wood). The surface is very rough when dry and takes on a bone white almost ghostly appearance, devoid of luster and character.



From the original questioner:
By itself, is sodium hydroxide dangerous? I'm looking to somehow just remove the color of the alder radial grains and fleck streaks, for our customer's satisfaction. I've researched the three main components of what wood really is (cellulose, lignin and hemicelluloses) to determine which of these composites is what the grain is a part of. Do you know? If I find that out, I will focus on certain chemicals that react with and change the cell color of that composite (wood grain).


From contributor J:
Sodium hydroxide is very caustic and you should avoid contact with it. Splash protection goggles are important.

I can't say you'll do much for selectively removing the portions of the alder you describe. Typically to de-emphasize the grain and figure you mention, you'd use a bleachtone type ground stain. Follow that up with artful glazing and toning and you may have a happy customer.

In situations like this you can drive yourself nuts trying to achieve the look the customer wants. Can't you use another wood?



From the original questioner:
I agree this is a mammoth-sized project. If I pull this one off, just our cost savings alone in material re-capture would be beyond measure. I'm going to keep on it though. Maybe operating in a bit of ignorance as I go is helping right now.

At this point chromosphores are my focus.



From contributor M:
Jeff's suggestion to use a bleachtone stain and glazes is by far the best one so far. I use that sort of system frequently to get the subdued look that is popular in my area right now. You can tint the bleachtone to get the proper ground color, if needed.

What kind of overall color and appearance are you looking for exactly, other than to subdue the rays and flecks? Perhaps I could recommend a schedule to start from.

Another way to subdue the figure is to apply your stain in a dry coat, without wiping, but that usually ends up looking muddy to me. A pigmented toner does something similar and has been used a lot on furniture through the years.



From the original questioner:
My ultimate objective is to sell alder products that look like alder sapwood - no appearance of grain or fleck. Can Bleachtone help with this?


From contributor M:
Could be. It really depends on how you are finishing the sapwood now, and what kind of overall look you're after. Bleachtone type stains subdue the natural figure in the wood, and the glazes over it can highlight the pores (or not, depending on technique.)

The alder I have in my shop is pretty contrasty, and if you are finishing it "natural," there is no way to subdue the figure in the wood.

However, if you are already using dye and pigment stain to even out the color, it could be possible.

As I wrote before, it all depends on the end look you are after. I have made maple legs exactly match the mahogany sides on an old Steinway piano, and I have made an oak floor look like walnut burl, among other things (some of which I'll never do again!)

Almost anything is possible - the problem is to do it economically. What is your current finishing schedule? Perhaps you could post a photo of the look you are trying to get? If I can know a little more clearly what you are doing now, it would be possible to give you a better answer.



From the original questioner:
I think the Bleachtone will work especially on the material that will specifically need this sort of application. They always say that water is to be used as a wash down agent for getting the bleach out. Is there a safe solvent-based liquid that does this? I'm trying to get away from the raised grain problems because we would have to bleach our handles after they are shaped/sanded and we won't be able to sand them again. Any thoughts?


From contributor M:
Bleachtone stain isn't a bleach at all, but rather an extremely thin-bodied, pigmented stain made by M.L.Campbell. Another brand is called Blond-It. Bleachtone comes in white only, but can be tinted to create the desired ground color. Blond-It comes in various light shades, if my information is correct.

In use, you thin it appropriately and spray on a "just wet" coat. It sinks into the wood and flashes off within seconds, leaving a bleached appearance. The figure of the wood still shows through, but is more or less subdued, depending on how you apply the stain.

I still don't have any real visual on the look you are after, but my first inclination would be to make up a blonding or bleachtone stain tinted close to the lightest color in your sapwood (wet). I would apply the stain, and then seal with vinyl sealer. You can thin the sealer more or less, depending on how you want the glaze to pick up the grain or pores. More sealer yields less grain. For some finishes I just wash coat and scuff sand, but usually it's a half or full coat of sealer.

Next I would apply a glaze of the color you choose, and wipe off hard. The glaze will lodge in the pores of the wood and bring up the grain. It will also alter the overall tint slightly. (A wiping stain is sometimes appropriate here instead of glaze.) Go easy with the glaze, just kind of fog it on and wipe it off with a soft rag. I can usually do a large kitchen with just a quart or so.

Seal the glaze in with vinyl sealer. (You can glaze again with a darker color to give some more depth and richness to the finish, or just to antique it a bit. Be sure to seal each coat of glaze.)

After everything is glazed and sealed, just topcoat with your finish of choice.

That's where I would start. Then I would alter the color and intensity of each step until I had the look I wanted. For production finishing, it is by far best to mix the materials so that they yield the desired result very easily, without excessive manipulation - spray on, wipe off.

Regarding bleaching in production, I would have thought it prohibitively time consuming and expensive for production, but I read a chapter from a book called "Furniture Production - furniture finishing textbook" that outlines the process…

Maybe we're attacking this thing all wrong. If you're using plain-sawed alder, you're going to have this unwanted figure on less than 10% of your wood, and usually on just one side.

Would it not be more economical just to turn the bad faces to the side that doesn't show? Might be a lot less trouble in the long run...



From the original questioner:
We make small wooden handles for the Paint Sundry divisions. Everything shows 3-D. In a shaped or turned product the wood rays are accentuated even more. Then on top of that they want a non-wetted transparent looking coating that is water repellent. For moisture resistance I'm looking into Dimethicone. We use a simple acetone/silicone mix. Maybe the addition of the Dimethicone will help, providing its soluble with what I'm using. That formulation doesn't seem to accentuate the grain any. We've also dinked with a fast-dry Hexane solvent and soluble wax additive. It works good for the above mentioned problems but seems to shrink the wood body of our product beyond the desired spec. Especially in the critical areas. Besides that the stuff kind of stinks. But for this continued "hiding the grain" thing, I'm going to be on that for awhile.

Ask me why our customer doesn't like wood grain - the short of it is their marketing department perceives the grain to be a potential crack or weak spot. Also they're being very competitive with other shelf living wholesalers who compete with them. It's quite a thing really. The furniture guys and forestry folks we work with get steaming mad at our customer for doing all that. They are our biggest customer though, and at the same time efficiently getting more of what they want would literally yield us a 50% increase in shipables.



From contributor M:
Oh. Now I understand a little better. You definitely want something less labor intensive, if possible. Can't use some plain vanilla wood like soft maple, poplar, or one of the less grainy birches?

If you have to use alder, you could just seal the wood, put some pigment or dye in your first coat of lacquer, and color it with that, then topcoat. It would sure subdue the grain and give you a "flat" look, and it would take a lot less labor.

I didn't suggest this before because I was thinking furniture, and it's pretty hard to do raised panel doors and other complex shapes with this technique, but paintbrush handles should be a breeze. Just watch for runs...

Pigment in lacquer would give you the most hiding, but dye in lacquer would give you a transparent, flat look. Try them both before you commit to all the excess labor of ground stain and glaze.

Forgot to mention: Sealing first, then coating with colored material is adaptable to a dip line and I know there are finishes that are thin enough to not appear to build a film at all, especially if you use a flat topcoat. I use a thin build of flat Duravar to give the look of an "oil" finish with a ton better performance. Works with regular lacquer, too.

This is getting beyond my area of direct experience, but any good industrial coatings supplier should be able to point you in the right direction from here.

There are still limits on what you can do. Silk purses and sow's ears, for example.



From the original questioner:
I will consider your advice on layer coating the wood into another cast or tone. If it works for us in the lab, then we can figure a way to do it out on the production floor.


I haven't read any comments on using oxalic acid as a bleach. For me it is not as rough on the wood as sodium hydroxide, yet removes a good bit of color. Rather than using the customary crystals, I have found Home Depot sells it already mixed in the form of Behr Fence Cleaner. What's the group opinion?


From contributor J:
Oxalic acid may slightly lighten a wood color, but in most cases all it will do is remove weathering and graying. To bleach a wood of its natural color, it's not effective.


I am interested in an older boat which has an all teak interior that has turned very dark. What product(s) work to lighten and clean it best?


From contributor J:
On an interior, it's probably just old, dirty and oxidized varnish. Stripping the finish off first is the first step in lightening an old finish. See if the color is okay after stripping and then decide if you need it lighter with a bleach. Do a web search for Te Ka Teak Cleaners.

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