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| Chemical Treatments? http://www-.luthiersforum.com/forum/viewtopic.php?f=10102&t=11374 |
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| Author: | Telfer [ Sat Mar 24, 2007 4:31 pm ] |
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One of my favourite books on finishing is one called 'Wood Finishing with George Frank'. It talks a lot about what cabinetmakers used to colour wood back in the days of yore, before the dawn of aniline dyes, a little over a hundred years ago. They used all kinds of vegetable and insect dyes...logwood extract, black tea, boiled walnut husks, and so on, but on high end peices woodworkers apparently prefered to use chemical catalysts like ferrous sulfate, ammonia, potassium dichromate and potassium permanganate. For bleaching wood a strong organic acid called oxalic acid was used, and this is what interests me at the moment. I just bought enough black walnut to make three necks (halfway through the first one), but its a little too dark, so Im wondering if anyone here has had any success with oxalic acid to lighten wood. Of course Im going to try it on some scrap peices...but first I have to go find some. There used to be two chemistry shops in town, but they seem to have blown away. |
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| Author: | David Collins [ Sat Mar 24, 2007 6:44 pm ] |
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You may go through hoops searching for oxalic acid in chemistry shops only to find that the off-the-shelf wood bleach in your local hardware store is just what you're looking for. I believe that most commercial wood bleaches are still primarily oxalic acid, and many will come with a part B which would simply be a basic solution to neutralize the acid. Any retail wood bleach should have a number for an MSDS sheet, which should tell you much of what it contains. I'm lucky to have a bowmaker upstairs from my shop who is liscensed to purchase many chemicals not available to the public. I don't have much use for many, but the harpsichord builder I used to work with uses nitric acid for coloring his boxwood key covers. Of course the more traditional method was simply to bury them in horse manure for six months or so, but straight nitric acid is much faster (and a bit more sanitary as well). Ammonia can be used to darken more acidic woods like oak, but I don't know how many woods in our trade would be significantly affected by it. I've experimented with ferrous sulfate on birdseye maple, but was unhappy with the blueish tint that I couldn't seem to get rid of. I've still never tried potassium chromate, although I've seen some examples of beautiful "grain popping" on mahagony. I've never tried anything with potassium permangenate either. |
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| Author: | Telfer [ Sat Mar 24, 2007 8:13 pm ] |
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[QUOTE=David Collins] You may go through hoops searching for oxalic acid in chemistry shops only to find that the off-the-shelf wood bleach in your local hardware store is just what you're looking for. I believe that most commercial wood bleaches are still primarily oxalic acid, and many will come with a part B which would simply be a basic solution to neutralize the acid.[/QUOTE] Well I dont want to buy anything unless I know exactly what it is...George Frank recommends dissolving the pure oxalic cystals in alcohol, not water. Its apparently over twice as soluable in alcohol...plus I dont like the idea of dowsing a neck in water for any length of time. I thought the two part bleaches were the peroxide formulas??? Interesting note on the horse manure trick...now I know what to do when someone asks me to 'relic' their Telecaster! |
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| Author: | jhowell [ Sun Mar 25, 2007 5:01 am ] |
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This site appears to have oxalic acid plus a lot of reading material. I've not ordered from them, but it sure looks like a good resource for historic wood finishing technique and materials. woodfinishsupply |
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| Author: | David Collins [ Sun Mar 25, 2007 9:04 am ] |
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Check out DAP wood bleach. It's one of those brands most likely to be found in any hardware or box store. It appears to be 100% oxalic acid crystals meant for disolving in water, but I'm sure you could use alcohol instead. I've never checked out George Franks book, but I believe Michael Dresdner has a book or two out on wood finishing as well. He came to a seminar we had many years ago, and his knowledge of the chemistry of wood was quite impressive. I still have a several page list buried somewhere of useful chemicals for manipulating wood, but don't own any of his books. I'll have to look up the Franks one. |
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| Author: | Telfer [ Sun Mar 25, 2007 10:32 am ] |
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[QUOTE=ToddStock] Oxalic acid has minimal bleaching capability, but is great for removing iron staining - I use it when I need to remove iron staining from tannin-ladden wood without shifting the base color. Def not what you need to bleach walnut. Two part peroxide-based bleaches are used to uniformly lighten wood for application of dye or stain - I use them when I want to take mahogany or other medium to medium dark woods to a light color for a natural blonde look that was popular in the '50's. Peroxide bleaches will not do much on rosewood, ebony, and other very dense tropicals. Clorine-based bleaches lighten some woods, but tend to leave a yellow cast, and are not as effective in my experience as A/B peroxide formulations.[/QUOTE] Well I had no trouble finding pure oxalic acid this morning - local paint store. I made a saturated alcohol solution and soaked my walnut repeatedly for about 15 minutes - then left it alone to dry out. No clear verdict yet, but it definitely lightens the wood. It remains to be seen what the lighter colour will look like under a finish. It may be too whiteish. As soon as I get my new camera battery in the mail I'll take a picture of my test board - half treated and half untreated, so you can see the difference. Ive been warned in books that peroxide may be too strong - erasing the figure??? I tried clorine years ago on some furniture, and no matter how well I rinsed (water and vinegar) it always smelled vaguely like bleach...never again! |
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| Author: | Telfer [ Sun Mar 25, 2007 10:39 am ] |
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[QUOTE=David Collins]I'll have to look up the Franks one.[/QUOTE] I believe its out of print, but I get all my second hand books from abebooks.com http://www.abebooks.com/servlet/SearchResults?sts=t&y=0&tn=w ood+finishing+with+george+frank&x=0 George Frank used to run one of the best antique restoration studios in France back in the day, and has lots of good stories about the finishing tech of the last century. He was also the answer man for 'Fine Woodworking' magazine some years ago. |
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| Author: | Telfer [ Sun Mar 25, 2007 10:59 am ] |
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[QUOTE=Telfer] No clear verdict yet, but it definitely lightens the wood. [/QUOTE] Actually no, Todd was absotlutely right! I just wiped the board down with mineral spirits and the treated area is NOT 'significnatly' lighter in colour...oh well. |
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| Author: | Telfer [ Sun Mar 25, 2007 1:41 pm ] |
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[QUOTE=ToddStock] Try an A/B peroxide bleach on some scraps...follow the directions and neutralize! Depending on how long the bleach gets to work, you should get a uniformly lighter surface that still shows the figure once dye-stained to the desired shade. [/QUOTE] Its not going to be dyed, just finished as is...but I'll take your advice and proceed with caution, thanks! |
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