Fuming With Ammonia

Discussion in 'Tutorials and Tips' started by Rob Wallace, May 21, 2009.

  1. This post copied from an earlier thread "Best finish" for sycamore to allow people to search on this method in the 'How To's, Tips, and Techniques' category:

    Originally Posted by cwearing
    What is the chemistry behind the amonia fuming. Also, please describe the procedure for the fyming process.

    First, I am not a chemist; I only have some very limited knowledge about the chemistry of the ammonia fuming process. My assumption is that there is a differential deposition of tannins or other polyphenolics that are more concentrated in the darker 'fleck' areas, relative to the paler background wood cells. Ammonia (or ammonium ion) interacts with these compounds and produces either some form of complexing, or establishing chromophores that absorb more light (?). [I would be happy to learn more details and obtain a better explanation about the chemistry of this process from organic or natural products chemists.] (My earlier experience with ammonia fuming was in the lab, studying flavonoid mixtures from plants that were separated on 2-dimensional chromatograms, using ammonia fuming and viewing UV light to observe chromatic shifts in fluorescence to identify the separated compounds).

    In sycamore, the ammonia fuming will slightly darken the background 'pale' wood, but will selectively darken the fleck features to a greater level of 'darkness', heightening the contrast (there may be some variation between batches of wood as to ability to establish this contrast). It has long been known that fuming cherry, for example, can produce a deeper, richer tone in the wood. I have also found this true for Goncalo Alves, which deepened the color intensity on the darker areas (presumably with more tannins or other extractives), and was only of minimal influence on the lighter (sapwood) areas. There is much room for experimentation here...

    As to the fuming process, it is fairly simple. The unfinshed (but sanded) wood piece is placed in a closeable container (or "tent" if very large) - I use a gasketed-lid 5 gallon plastic container (such as a "drywall compound bucket"). A small container of liquid ammonia is placed into the large container with the piece to be fumed, such that it does not touch the wood. I support the turned wooden piece off of the bottom of the large container (a small amount of wire mesh works OK) so that ammonia fumes can reach all sides of the piece at the same time. I use laboratory grade concentrated ammonium hydroxide for this, but household ammonia sold as a cleaning agent will work as well - it just takes longer. A rolled-up piece of paper towel that extends above the rim of ammonia vessel (I use a 250 ml glass beaker) serves as a "wick" which provides more surface area for the ammonia to evaporate from. Partially fill the ammonia container with liquid ammonia solution after the towel is saturated. The large container is then sealed, and the fumes are allowed to concentrate and interact with the wooden piece until the desired effect is reached. This may take one day, one week, or even more time - variables include the species of wood used, temperature, ammonia concentration, and probably some individual variation in the specific piece(s) of wood being used. It's a trial and error - "wait 'til it looks good" - kind of process.

    A word of caution - Ammonia vapors are noxious, and in high concentration, dangerous. I would not advise doing this procedure in an indoor shop/studio unless there is a VERY good ventilation system available. When I do ammonia fuming, it is usually done in my garage from spring to fall when temperatures are high enough to do this within a reasonable period of fuming time (I live in Iowa, with cold, often "sub-zero winters"). To check on the fuming progress, the cover is opened carefully outdoors, so as to avoid breathing the fumes; I stand upwind so that I do not encounter the escaping ammonia fumes. (When I've ammonia fumed in winter months, I do it in my lab at the University, and uncover the container within a chemical fume hood - one of the perks of being a science nerd!) As might be obvious (or not?), do not breathe ammonia fumes, use proper eye protection, and avoid getting liquid ammonia on exposed skin.

    Once the piece is "done" to the desired level of darkness, it is removed from the fumes and allowed to out-gas and dissipate any residual ammonia vapors. This is usually completed in a day or two, depending on temperature. You can easily tell when this is done by cautiously sniffing the piece.

    Because the fuming was done in an enclosed, highly humid container, there may be wood fibers raised during this process (you can easily feel if this has happened). Some light sanding with 320 or 400 can usually remove these "out-standing" fibers without cutting too deeply into the wood surface. From there, I seal with 1# shellac and then spray lacquer as noted in my earlier post.

    Hopefully this is clearly explained enough for others to try the process...
    Let me know if there are questions....

    Rob Wallace
     
  2. Owen Lowe

    Owen Lowe

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    I have fumed quite a bit of cherry and white oak (red oak takes on a green cast) using blue print ammonia (28% as I recall). If you are using anything stronger than household ammonia, make sure you do it at a location in which you can escape easily from the vapor should some be spilled. (I think an amount of less than a 1/2 cup or so of the 28% variety would be enough in an enclosed room to cause marked irritation - it's powerful stuff.) Also make sure pets and children are nowhere near.

    RE: your skin: Contact with the vapors alone will tell you where every skin abrasion is located! You'll feel stinging where you didn't even realize you had a nick.

    Excellent reply Rob.
     
  3. Joe Greiner

    Joe Greiner

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    Re: Blueprinting ammonia: Avoid shaving for a couple days beforehand, if you can. BTDT.
     
  4. Jake Gevorgian

    Jake Gevorgian

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    Thanks to you AAW forum is now Woodturning Encyclopedia :) That was a great coverage.
     
  5. Hugh

    Hugh

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    Blue print ammonia or "Aqua" ammonia (used as a fertilizer commerically). The last time I went to a blue print shop - they had converted to a closed up tank (kind of like a propane tank setup). Large farms in the Central Valley of California use Aqua for a fertilizer. I believe it is about 22%.
    Hugh
     

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