Force-Aging Wood

Lee Bussy

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I would like to force age some wood and I have seen pics and discussion online that leads me to believe that I want to use ferrous sulfate instead of ferrous acetate.  I looked around to find some and about the only stuff I can find is lawn care (~35%), iron sulfate for oral ingestion (~25%) and iron sulfate liquid for oral ingestion (~19%.)  Has anyone sourced this differently?  I'd think the filler in iron tablets would just be starch, sugar, etc. 

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What species are you working with? I know the iron acetate reaction varies widely with different species.

Well this one is a small project my wife wants done .. pictures on wood.  The medium will likely be clear pine.  I don't expect that to be very high in tannins, so I will likely do a tea wash first.

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Lee, I have done the iron acetate thing on pine a few times. It takes 2 or three days after application (unsealed, I guess it is an oxydizing reaction), but pine will turn a rich medium brown. I never used the tea wash trick.  I'm expecting the iron sulfate will produce a more bleached / driftwood appearance. Please share your results.



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  • 2 weeks later...

Thanks, Lee! Very clearly stated experiment. I appreciate this level of detail, and find it very helpful.

To me, it appears that the samples without the tea wash have an even, blotch-free color, whereas the tea wash seems to deepen the grain contrast. It also appears to cause some streaking, but I suspect that may be a result of applying the solutions while the tea was still wet. In any case, this looks better than pigment stains usually do on pine.
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This was a raw board from the scrap pile - no sanding.  There is some blotching but some is due to splashing one solution into another area.  There's also some sap that's come out of the board, and one area looks as if I may have gotten some silicone spray on it.

As it drys it looks nicer.

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Cool stuff Lee.

I wonder how light fast the samples (especially the tea) would be. Is the final color of the samples with tea applied due to staining by the tea or is it from a chemical change caused by the tannin? I suggest ripping the board in half and then putting half out in the sun and half in a dark closet. Vegetable dyes are notoriously fugitive. Paint a picture with pomegranate juice and it will be like alizarin crimson. Apply sunlight and you will soon have brown, somewhat like the color change of padauk or poplar.

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Well remember this is to distress wood so the more it weathers and is out in the sunlight, the more natural patina is gained even if the false patina goes away.  This is not a dye so much as a chemical reaction.  The tea makes no color change and it takes about 10-20 seconds before you see any change when you put one of the iron compounds on the wood.  It's like it "develops."

If I think about it I'll rip it and put it out in the weather.  I suspect the winter sun won't do much.

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  • 4 years later...

Well done Lee.  Great foundation work for a lot of us. I work with a local mill here in MT that produces circular saw cut rough lumber from Douglas fir which ages to a pleasant pinkish color in about a year. Some folks are asking for a barn wood finish 

I have a few year on this old clock and living in montana I have seen quite a few barns so I have no idea what they have in mind for “barn wood” .  This thread has helped a great deal.  I’m  pretty good at woodworking but not much of a chemist so this helped a bunch.  For me the Ferrous acetate gives the Douglas fir a warm brown after 24 hours  I ll call this barn wood and see we’re it goes.  Ferrous Sulphate does not seem to do much as you indicated.  
Thank for the help

Forester Tom



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