Chemistry Quiz...Why does my wet maple turn purple?

[llucas]

So I have been turning some very wet ambrosia maple and have a puzzler for you chemists and other smart people. Why do blotches of purple appear within seconds of turning it? I'm not talking about the smudgy grey/black moldy look that you find the next morning sometimes when restarting an unfinished turning. This appears suddenly just like the old iodine solution on the potato test for starch. A very dark almost black purple appears where the chuck jaws have bitten into the tenon.

I suspect it is a chemical reaction with something on the turning tools and on the chuck.
Anyone see this? Cure?

 

[sawman101]

I've experienced the reaction years ago when gluing up white pine for panels, and the black pipe from the clamps touched the wood. It is a chemical reaction between the minerals in the metal and the minerals in the wood. I remember sawing ash logs in my saw mill many years back, and watching the pretty colors appear as soon as the board was loosed from the cut. There it was the wood being exposed to the air. I cannot explain it, but it's interesting, and annoying at the same time.

 

[Dan Bowman]

It's caused by a reaction between the wood's tannins and iron (ferrous) ions from the chuck. It's amazing that solid steel can transfer enough Fe by mere contact to allow the reaction to proceed, but it does.

 

[Jeff]

It's not uncommon. Wet wood with natural tannic acid + iron = iron tannate which is +/- purplish/black. Read about ebonizing wood with steel wool and vinegar.

https://www.thenavagepatch.com/aging-wood-vinegar-steel-wool/

The staining is mostly superficial so it should sand off easily. You could try wrapping the tenon with plastic wrap before chucking and turning but that may be much ado about nothing too.

 

[llucas]

Yep...it sanded off with a little effort....guess I learned something....Thanks for the answer guys.

 

[cyclopentadiene]

I am actually experimenting with this exact same chemistry right now. I just completed building a workbench from ash. My plans are to ebonize the base, use a walnut band around the top and clear coat everthing with lacquer.

in order to ebonize, I have made a solution of iron acetate by placing a steel,wood pad in vinegar (5% acetic acid) for a week. In theory, this just brushes on and leaves an ebonize day finish. It is supposed to be excellent for oak, walnut, cherry and mahogany as they are high in tannin content. It also works on ash but generally needs the,piece to be treated with tannin beforehand as ash is lower in tannin content. I experimented with a piece of scrap using the solution alone and it provides a very nice brown color similar to chestnut. It worked great on a scrap of walnut but the black finish looks blotchy.

internet descriptions (popular,woodworking and Brian Boggs sources) of the process suggest using bark powder tea made from a product available to taxidermists. An alternative is to use multiple packs of black tea in a single pot of hot water. I plan to try both to see what I like best.

I am a chemist so the combination of chemistry and woodworking fascinates me. As an example, I always fume cherry and mahogany with ammonia as it leads to a more rich color than clear coat alone. The other process I want to try is,wood bleaching.
once I receive the bark tea and other supplies, I will post photos of different woods and different treatments.

 

[Jeff]

internet descriptions (popular,woodworking and Brian Boggs sources) of the process suggest using bark powder tea made from a product available to taxidermists. An alternative is to use multiple packs of black tea in a single pot of hot water. I plan to try both to see what I like best.

I'm an organic chemist too and I did a bit of ebonizing experimentation about 3 years ago out of curiosity. I read several articles about the process including the one by Brian Boggs about the quebracho bark tea having a higher tannic acid content than plain old regular household tea.

With that background information I decided to jazz up the tannic acid component because I wanted to try some wood species that have a low tannic acid content.
Bought a bag of purified tannic acid for starters and I can mail some to you if you wish.

​

The iron (II) sulfate was made from oil free 0000 steel wool and glacial acetic acid (97%), not household vinegar (3-8%). It's much quicker and ready to use in about 1 hour instead of days.

https://www.wwgoa.com/article/ebonizing-wood/

 

[llucas]

I appreciate all the input and especially the discussion of ebonizing with tannic acid donors.
I do wonder if maple without augmentation is notable for its tannic acid concentration.
Could it be something else? sugar? starch? in the maple wood?

 

[Jeff]

I appreciate all the input and especially the discussion of ebonizing with tannic acid donors.
I do wonder if maple without augmentation is notable for its tannic acid concentration.
Could it be something else? sugar? starch? in the maple wood?

Maple is not known for its high native tannic acid content but that can vary +/- in the same tree so you should try a few of the homemade concoctions and see what you think. However, a few boards from tree #1 may react differently from tree #2 boards. We can level the playing field a little by adding the tannic acid solution to the wood.

Could it be something else? sugar? starch? in the maple wood?

No, it's the tannic acid + iron = iron tannate and that's the color.

 

[Mike Mills]

I've had the same problem with wet oak.
A little lemon juice, *RealLemon" is OK, and it disappears from the wood, tools, lathe bed, hands....