how to stop tannins leaching from wood?

[DMcIvor]

Among the items I make are shaving brushes, which I create using a variety of hardwoods for handles. Knowing the brushes will be exposed to water, I finish the handles with tung oil in an effort to create the best water barrier short of a two-part epoxy. After the tung oil has set, I coat the handle with a layer of paste wax.

Recently I had a client report that dark tannins are leaching from the cocobolo brush I made for him, staining the brush head, towels, probably skin, and anything else it comes in contact with!

Anyone have any ideas for how to prevent this from happening? Besides staying away from cocobolo, walnut, blackwood, and all those other high tannin woods?

 

[Bill Boehme]

Well, tan my hide.........

Tannic acid reacts strongly with iron and produces a black stain and I suppose that it could also cause some staining if the water has a lot of dissolved iron, in which case everything is stained anyway. Buy a box of lye crystals and soak the piece of wood in a mild solution for a day or so. It will remove a good deal of the color from the wood, but, hey you can't have it both ways and it will hold the leaching of tannin in check. You could soak the piece of wood in water for about 3 months and it might remove most of the tannin close to the surface. No charge for the free advice.

Second thoughts -- reread your post: Cocobolo, you say -- may not be tannin -- it is an oily wood with a lot of reddish "resin?" Maybe a lot of solvent and rags would work, but I am not sure if cocobolo ever completely quits oozing red stuff. I used up a pile of rags and a can of solvent on a large board that I have and still haven't made a great deal of progress. I believe that I would stay away from using oil on cocobolo because the stuff may never dry. Maybe just polish to a high finish and leave it bare -- cocobolo should handle water just fine by itself and doesn't need any additional help.

Bill

 

[dkulze]

I'd recommend multiple soakings in eurythane oil. You'll find that it's harder and more water proof than tung.

When exposed to water, paste wax clouds. A eurythane clearcoat finish or laquer finish over the soaked eurythane will help.

Good luck,
Dietrich

 

[MichaelMouse]

Well, first thing is to remind you that tropical woods with their multiple and multicolored poisons are still used as dye sources. Tannins are semi-effective at keeping browsers away from bark, leaves and twigs, but no where near as effective against bugs and rot as the stuff in tropical woods, or even cedar.

They are, of course water-soluble, so you could boil your stock to get the casual overage out. Might not look as good as the unboiled. My boiling and microwaving attempts never did. I think I'd go with over-drying by baking the turned product in the oven, then submerging the warm partial vacuum wood in my finish. Which wouldn't be tung oil, but something a bit harder, like the urethane resins or even alkyd, in a flexible formulation like spar varnish. I remember my old wooden brush moved enough to splinter the paint off in lengthwise pieces. Imagine all brittle finishes would be close.

 

[woodwish]

I agree that it may not be the tannins. I'm not a chemist or "wood-oligist" but I know that cocobolo has a really oily content, in fact I have hard time trying to get any oil finish on it. I think the oil is what is leeching out instead of tannins. I've never had problem with walnut leeching out any color but cocobolo will stain about anything it contacts. I have dealt with cocobolo problems by eliminating it from my inventory, not due to staining but any contact with it really makes my skin break out like poison ivy. Hard to turn and scratch at the same time so I gave all of mine away.

 

[Rob Wallace]

Not likely tannins alone....

I doubt that the extractives leaching out of the cocobolo are tannins alone. As others have suggested, it is likely a mixture of oils and other pigments that are found in cell wall and in intercellular spaces that are the culprit. A temprorary fix might be using mineral spirits (or if more agressive action needed, lacquer thinner or xylol), to try to remove some of the leachate, but it likely will not fully resolve the problem over time. Dalbergias, in general, are full of extractives (which is one of the reasons why they are so pretty), and the oiliness does not help. As attractive as this wood is, it is likely not the best choice for this application.

Short of fully embedding the wood in epoxy or a catalyzed lacquer finish, I don't know how much more you can stop the leaching problem, particularly if it is to be used around water constantly. What about trying ipe or Lignum Vitae (although the latter is also oily)?

Good Luck,

Rob Wallace
(Full time "plant-ologist" and part time "wood-ologist")
Iowa State University
Ames, Iowa