Two-part wood bleach questions

Re: Two-part wood bleach questions

Bill Tindall, E.Tn.

I have no experience bleaching walnut, but do understand the chemistry.

Does the sodium hydroxide-to-hydrogen peroxide ratio have any effect on the bleaching power? yes, follow directions

Does the order of application matter when using the liquids separately? I would think NaOH first, but again follow directions.

Strong hydrogen peroxide decomposes over time. It is possible your material ahs lost some oxidizing power.

Rushed finishing jobs usually lead to refinishing down the road.

Used it once...

John in NM

I did not like the results. The bleach seemed to make the wood surface more porous and it did not stain well afterwards.

Walnut is easy to lighten - leave it in the sun. Out here that only takes a maybe a day (7000' elevation), leave it a week and it looks like pine, a month and it just about turns grey.

Another idea

David Yoho

I wonder if oxalic acid would do the trick. This is most often used to bleach or lighten dark stains on wood surfaces. It's easy to get and use. The ratio doesn't have to be mixed exactly with warm water but does need to be rinsed off with clean water. A sponge can be helpful with this. Couldn't hurt to try it.

Re: Two-part wood bleach questions

Don Stephan

As mentioned, black walnut lightens significantly with exposure to sunlight, so it is unsure how the bleached/glazed panel will look in a few months.

Re: Two-part wood bleach questions

Dick Coers

I've done some unorthodox coloring over the years to age or mimic other wood. Used pea green stain once on red oak to make it look like white oak. Used thinned garnet shellac to mimic aged and yellowed clear coat. Once used bright orange stain on walnut to mimic an aged color. On a short deadline like you have, good enough will be the rule of the day. Out gassing done by the weekend is certainly an unacheivable expectation. Could be correct color is too.

Re: Two-part wood bleach questions

hapajeff

I appreciate the alternate solutions, and figured a workaround both for the color and for the timeline, but my original questions remain, though more out of curiosity now.

As I mentioned, this bleaching process is still leaving a fair amount of color. I'm wondering if anyone here has had direct experience using the two part bleach to remove the color from walnut and what I might do to lighten walnut further because three applications haven't gotten the wood light enough. I swear we used to get the walnut lighter than butternut at my old job, and the current project didn't get close.

The manufacturer's instructions say to mix the two parts equally and apply them. In a phone call to Wood Kote, I was told I can alternatively apply the lye liquid first and then brush on the peroxide "after a little bit." When making the call, I didn't think to ask how much time that was.

Maybe someone can explain the process and why it works.

Re: Two-part wood bleach questions

John in NM

That's odd, I would have guessed lye followed by peroxide would tend to darken wood, kind of like letting it age for decades in a shed..... I have a French walnut stock blank that I was experimenting with darkening slightly that way.

Maybe at your old job oxalic acid was the bleaching agent?

I'm not sure which it was I had such bad luck with, that was 20 years ago. I recall it being two parts in separate applications though. The boss wanted sycamore to look like beech. After that I swore to never try matching one wood to another again, it was painful to look at that table top...

Re: Two-part wood bleach questions

hapajeff

If used separately, basic Google research indicates using the sodium hydroxide first. You appear to be correct in that leaving it on too long will likely darken the wood, so it's advised to put the hydrogen peroxide on in short order.

No, we definitely didn't use oxalic acid to lighten the wood. If I'm not mistaken, that's used mostly to remove staining (versus removing the wood color).

The chemistry

Bill Tindall, E.Tn.

Colored chemicals are large complicated molecules because it takes a large complicated molecule to get their electron arrangements complicated enough to absorb visible light, especially red light. Color is a result of absorbing some color from the white light of the sun (or LED light).

Peroxide is a nifty molecule, it can soak up electrons from (oxidize stuff), or donate electrons (reduce stuff) to, other molecules. How it behaves depends on pH. In the presence of strong base peroxide becomes a powerful oxidizing chemical, that is to ,it will yank electrons out of many kinds of complicated molecules. When it yanks electrons out of a large complicated molecule (walnut colored chemicals for example) they usually become unstable and break into smaller molecules. These smaller molecules will only be able to absorb blue or even only ultraviolet light. The result will be yellow or colorless left behind chemicals.

Again, I have never bleached walnut. But if I was going to I would follow directions. If the result was insufficient color bleaching I would add heat from a heat gun. Slather on bleach and heat. Phenols in the wood will neutralize the NaOH. So I might try adding some more. If by some means, like guessing, I thought I had enough NaOH, I would just add more portions of peroxide, w /wo heat. If nothing worked I would conclude the peroxide had decomposed, or was not strong enough to begin with.

Re: Two-part wood bleach questions

Bill Tindall, E.Tn.

Oxalic acid will remove iron stain by making a colorless combination with iron. I doubt it will do anything with wood color.

Re: The chemistry

hapajeff

so, where does the sodium hydroxide fit into the equation?

to repeat.....

Bill Tindall, E.Tn.

Peroxide is a nifty molecule, it can soak up electrons from (oxidize stuff), or donate electrons (reduce stuff) to, other molecules. How it behaves depends on pH. In the presence of strong base

the strong base is sodium hydroxide.

Now that makes sense...

John in NM

What I was trying involved a pause between the two, long enough for the wood to dry - perhaps that could change the effect compared to the wood bleach manufacturer's instructions.

I didn't know peroxide was so versatile, I was just using it because I figured it would donate oxygen.... I may try this again with just the peroxide, I still haven't made anything from that stock blank.

Re: The chemistry

hapajeff

If the peroxide is what does the bleaching and the effect is somewhat determined by how strong the sodium hydroxide is, then it seems it would be better to apply the peroxide first and "control" the bleaching with the lye solution, right? If that's the case, then it seems like info on the 'net might be wrong, suggesting the lye be applied first if applied separately.

To your point about the peroxide perhaps being old and weaker, I've noticed that this new kit doesn't yield the same results as ones we used at my old shop, both in terms of bleaching and the observed reaction. Previously, I remember that the solution would foam mildly when applied. I got hardly any bubbling with this new box. Anecdotally, I've noticed that old peroxide for wounds doesn't seem to bubble on contact with blood nearly as well as new stuff. I suppose I should look for a manufacturing date on the wood bleach box now.

Re: The chemistry

Bill Tindall, E.Tn.

better to apply the peroxide first My prediction, considering that I understand the chemistry but have never used it to bleach wood, is applying peroxide first is not optimum. Stuff in the wood is going to catalyze decomposition. Applying peroxide first could result in it being weaker before the base got added to make it a powerful bleach.

that the solution would foam it should foam

Re: The chemistry

John in NM

Yes, should foam. Peroxide loses oxygen with UV exposure I believe - that's why in the drug store it comes in opaque brown bottles. Even then I bet it loses some over time through the plastic bottle. New is better with peroxide.

more complicated chemistry

Bill Tindall, E.Tn.

unbalanced equations but you get the idea

H2O2 >> H2O and O2 bubbles: decomposition reaction, useless for bleaching but it makes bubbles. Can be catalyzed(hastened) by light and many chemicals, maybe even some chemicals in wood, I don't know for sure

H2O2 + e- (electrons) + wood chemicals + base >> water + other wood chemicals

sucking electrons from wood, an oxidation that may break apart colored chemicals in the wood and destroy color