Avoiding Green Tint when Bleaching Maple

      Some technical tips to help get the best results when bleaching new wood. July 3, 2008

Question
I am getting a green tint left when I bleach maple with 2-part wood bleach. Any ideas?

Forum Responses
(Finishing Forum)
From contributor A:
Reduce part a - sodium hydroxide by 5% increments with distilled water, decrease your neutralizer (acetic acid / vinegar to 1% - should be five as packaged). Raise heat in your shop, wash the surface off with distilled water a few times after neutralizing, and dry quickly with hair dryer if possible. If it's oak, apply a 5-10% solution of phosphoric acid before the bleach and immediately wipe the surface with methyl alcohol soaked rags. Let dry and then apply part one bleach.



From contributor B:
Are you using the kind of two-part bleaches that leave a crust on the surface once they have dried?


From contributor C:
If you are in need of a stable bleach-like color, use a titanium white stain and a water white top finish. You will never get a peroxide bleach or chlorine to not bring out strange colors or not change over time. You may need to play with a wash coat of color, and seal then shade or tone to achieve your desired color sequence. Jasco used to be right down the block from my shop. It does have its uses in the restoration field, but not for maple cabinets.


From contributor A:
I've been bleaching new maple for decades without color problems. The problem is not with the bleach but with the applicator not having a good or thorough knowledge of how to use or how to achieve the lightness desired. I can make new maple or other light woods as white as paper but you have to know how to accomplish this.


From contributor D:
I have found that when bleaching any species it's best to do it in direct sun. The sun's UV's are your best tool, as it activates the whole process. Of course you may not have sunshine yet.


From contributor A:
To contributor D: Sorry to disagree. It's the heat of the full spectrum light acting upon the bleached surfaces - UV, infrared, etc. *Heat* is the keyword here - you can bleach mahogany paper white on the darkest coldest winter day using heat supplied by either a Milwaukee heat gun or a hi temp hair dryer without any sunshine at all. It's known as hyperbleaching. The bleaching action is caused by the nascent oxygen released when contact of the hydrogen peroxide starts the reaction and the loosely combined extra oxygen atom is released, which causes the surface that it's applied to or on, to lighten ( in chemistry everyone knows nascent oxygen causes bleaching of the substrate its acting upon). Therefore, sunlight is not necessary to bleach a wood though the heat from the full spectral light sun definitely is very helpful.


From the original questioner:
Thanks for your help guys. No, this bleach does not leave a crust behind. I believe you are referring to oxalic acid. In my tests the oxalic acid seems to remove green after using the two part bleach though.

To contributor A: When do you apply the heat gun - just after water wash? Why? Or while chemicals are working? Why distilled water? Is filtered drinking water not good enough?



From contributor A:
Drinking water can still have ions that interfere with the process. The best to use is deionized water but distilled or triple distilled will normally suffice - deionized can get pretty expensive. If you have reverse osmosis you use in your house that equals distilled for purity. Oxalic does help the green tinge associated with bleaching, but is really unnecessary if you slightly dilute the lye and wash off any foam first. You apply the heat immediately after applying the HP - Part 2 - dry thoroughly with the heat and repeat till you're as white as you want to be. Then, use vinegar at 1% to neutralize the lye, then 3 times with clear water and then re-dry with heat gun. This will get you close to paper white if you need.


From contributor A:
Sorry, only repeat the HP - part 2 process - not the lye process. Apply the lye only one time, in other words. Tap water can still contain trace amounts of chlorine which will or can react with the hydrogen to produce hydrogen/chloride bonds which you do not want to happen. Never use tap water for any color bleaching or dissolving water dyes etc. As clean as you may think it to be, it is not.


From contributor B:
The *crust* I made reference to was not the crystals left over by the oxalic acid but the leftovers of some bleaches like Jasco. Don't let the bleach solution puddle on the surface as that can cause issues and eventually end up actually burning the wood. I like to spray on two part bleaches as I have better control over the way the surface is covered.

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