All,
Thanks very much for the suggestions about aging pine a month or so ago. I was inspired to buy some nitric acid and give it a whirl. I’ll post a pic when I put the finish coats on. The short version is (on old SYP, freshly surfaced) it looks super. Rich old brown, even throughout with no blotching, and shows some of the occasional highlights in red that old pines can have, and some of the iridescent highlights of really old pine. Most interesting was that the solution was none-additive: it did not matter how much I put on in one spot, the tone remained the same. There were no lap marks and I could not seem to over-treat one area, even when going back to touch up a place the solution missed. Even smells like old wood. Other than turning one of my old but still good PurdyTinexNylon$14SashBrushes into a scrub brush, all went well. I wore fume mask, rubber gloves, & goggles and would never dream of doing without all that.
However, while holding the hair dryer for three hours, it occurred to me that the 9.5% solution, diluted 4:1 would dry, but what happens if the piece get wet again? Has the chemical action of oxidizing the wood permanently disassociated the acid, or will it be just as strong if moistened once more? My nightmare having a kid’s wet hand put on the piece and getting burned. Any chemists out there with an opinion?
Thanks,
JK
Replies
Sorry for butting in where chemists fear to tread (I'm not one, needless to say), but if I were doing it by the seat of my pants, I'd (a) rinse it thoroughly and (b) probably try bathing it in a mild basic solution (maybe baking soda) to neutralize anything left . Of course, I'd try it on a scrap piece first . . .
And now back to the professional chemists
It's a good idea to use a baking soda wash to neutralize - here's a link to info on chemical treatments for wood - http://www.homesteadfinishing.com/chemical%20dyeing.htm
Paul,
Thanks for the comments/link. I heard from my high school bio teacher who said that after oxidation, the acid turns into a gas and leaves, aka nitrous oxide, so there is nothing left. This contrasts somewhat with Jewitt's view (below). The brown color I believe is the result of the chemical burning of the wood, also called oxidation. It makes more sense that the NO2 would cause the new color rather than act like a dye or stain and be the new color. But my teacher also suggested trying a wetted piece of litmus paper on the wood just to check. I also used a solution far weaker: 9.5% diluted 4:1 than Jewitt suggest, and got results that I am more than pleased with, though skipping the heating with the much stronger mix would be very attractive. All that said, a little soda wash is really easy to do.
Thanks again,
JK
"Nitric Acid - Use this chemical in a 20% to 40% strength and always wear protective gear. This chemical duplicates the look of aged pine beautifully. Apply a wet coat to the wood and then heat with a hair dryer or heat gun to fully develop the effect. The nitrate ion (NO3) is converted to NO2 which is brown. I first heard about this treatment by a local artisan who uses it on curly maple gun-stocks and he says it's a well-known treatment in that field. If used without heat, it produces greenish yellow browns. If you can get a stronger solution, 65 - 70%, you don't have to heat it. This strength is hard to get, because of shipping restrictions, so you may have to settle for strengths below 40%."
I wounder if there is a chance you might end up making nitrocellulose (AKA gun cotton or atrilllery shell propellant) out of your cotton rags? It seems unlikely but you might not want to keep them around the shop.
Frank
Where can you get nitric acid? Thanks.
You can get it at a local printing, blue-printing, or graphics design supply house. If you have it shipped, you'll have to pay the hazardous materials charge (around $20 extra). Do a search on google.com for "nitric acid msds" before buying/using it to get a list of the safe handling procedures - it can burn your skin or lungs if mishandled - just work safely.
Thank you. Know the hazards but appreciate the warning.Gretchen
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