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Old Sep 02, 2010, 04:47 PM
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MYTH: Bending Wood by Soaking in it Household Ammonia Solutions

Definitions:
Household Ammonia - A solution of ammonium hydroxide, (ammonia dissolved in water) of approximately 10 to 15% by weight, classed as a chemical irritant.
Ammonia-based cleansers are based on further dilutions of 10% ammonium hydroxide solutions and are significantly less potent.
The strongest possible solution at 60 °F is approximately 35% dissolved ammonia by weight.
Anything 15% or over is considered a corrosive and over 25% is considered a dangerous material / hazmat.

The temporary plasticizing and subsequent bending of wood using household or the stronger commercial grade liquid ammonia cleansers is, unfortunately for us, a myth. As it has been repeated a number of times on RCG/Boats, here is the reality. Nothing you can purchase as a cleanser has a high enough concentration of ammonia to fully plasticize the wood nor can the ammonia penetrate into the wood deeply enough into the wood in a dissolved state.

>>> UPDATE: ClassicBoats has apparently had some success using 29% ammonia and a 24 hour soak... More in his posting here.

The process is believed to be as follows; gaseous ammonia is absorbed by the materials that "glue" the wood cells together causing them to loose their adhesive qualities. With these bonds weakened, the cells slip and slide past another easily allowing the wood to take on new shapes. The woods is then held in place in the shape desired, usually in a jig. The cellular "glues" regain their former bonding properties as the ammonia outgasses from the wood into the surrounding atmosphere and the wood regains its strength, permanently retaining its new shape. In fact, it has been noted that wood so treated is denser and harder than prior to treatment.

However, one-hundred-percent pure, gaseous anhydrous ammonia (DANGER: Poison Gas) is required, as is a stainless-steel pressure chamber large enough to contain your wood while holding a pressurized, corrosive atmosphere of 100 to 150 psi above ambient pressure (see the accompanying PDF file of the article by Bill Keenan that appeared in Fine Woodworking Magazine and started it all).

Further, you need to set up a system to capture the waste gas and dissolve as much of the it as possible in water using a "bubbler" made from a 55-gallon drum filled with water that waste ammonia is bled through. You will never capture all if it, so expect your neighbors to raise a stink. As one might imagine, this is not for the casual DIYer unless you are going to be bending a great deal of wood; being in the country with neighbors at least a few hundred yards away helps too.

Here is an excerpt from another article on extreme woodbending: "Although it’s beyond the capabilities and needs of most do-it-yourselfers, it is also possible to make some extremely complex bends in wood using anhydrous ammonia, (not the common household cleaning products), but it is extremely dangerous, and requires specialized equipment. It also darkens many woods. You can get more information about this process from “Understanding Wood” by R. Bruce Hoadley at your library, or from most online bookstores, etc… Also from Fine Woodworking, issue number 30 dated 1981 Sept/Oct., article by Bill Keenan. Experiments with ammonia bending have been conducted at the University of Wisconsin in plasticizing (making pliable) wood, via immersion in gaseous anhydrous ammonia… the theory being that the ammonia is used as a solvent, and diffuses into the cell wall structure and disassembles the existing microscopic cell components producing a more pliable wood...as the solvent diffuses out of the wood the wood cell components bond in new positions and retain that shape. Steam does the same job but ammonia plasticizes more completely and quicker. The key is the word anhydrous (anhydrous means without water), so the ammonia being referred to is chemically pure ammonia… NH3 in gaseous form (and it boils at –28 degrees Fahrenheit). Keenan notes that household ammonia is a dilute solution of ammonia gas in water and will not bend wood; however, although I have not tried it, a stronger concentration of ammonia is available from suppliers for use in blueprinting processes. Keenan and the U of Wisconsin procedure is done in a treatment chamber (autoclave) for introducing ammonia gas into woods...at 130 psi into a stainless steel container welded to withstand 800 psi of pressure. A combination of gaseous ammonia and steam is fed into a cylindrical container that the wood to be bent is placed in, exposing the wood for about 45 min. and it comes out like limp spaghetti. Working time to bend and shape plasticized wood is now about 15 minutes."

For future reference...
Here are a couple of archived forums from the Furniture Makers Society.

http://www.furnituresociety.org/dc/d...d=50&mode=full
http://www.furnituresociety.org/dc/d...1199&mode=full

Edit: Sept 03, '10 - Added chapter from Wood Handbook on "Specialty Treatments" of wood. First two pages are on bending.
Edit: Sept 07, '10 - Added MSDS sheets and a couple of suppliers of laboratory grade solution.
Edit: Sept 10, '10 - Added medical / exposure link
Edit: April 13, '11 - Added link to ClassicBoats write-up of his experience with a 29% ammonia solution and mahogany.

Medical
eMedicine (WebMD) - Ammonia Toxicity
Medline Plus - Ammonium hydroxide poisoning
Univ. of Maryland Medical Center - Ammonium Hydroxide Poisoning

The "real" thing....
http://secure.sciencecompany.com/Amm...P6379C670.aspx
http://www.coleparmer.com/catalog/pr...sp?sku=8822010
http://www.onlinesciencemall.com/Sho...d/0/rid/126318

Links of possible interest:
VeritasŪ Steam-Bending Instruction Booklet
Furniture Maker Tai-Workshop's Wood Bending Page
Heritage Boat Restoration using Cold-Bend™ Hardwood
Marine Applications with Compwood™

Do a Youtube search using "Wood Bending with Compwood - Compressed Hardwood" - Yields some really interesting vids. Watch a 2x4 nearly pretzeled!



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Last edited by craig_c; May 14, 2011 at 12:30 AM.
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