This is a very interesting article, especially since I'm an analytical
chemist and so mixing woodworking and chemistry is always a good thing, IMO.
A few key points that I would point to as the take-home messages from the
1) Referring to table 1, concentrate on the delta E column. The larger the
value, the larger the color change that the particular process had on the
wood. As you can see from the table, ammonia fuming had the most dramatic
effects, and did so in a much shorter time frame than the other methods. As
you can see, ethanolamine was at best able to only color the wood less than
one third as much as ammonia after 16 hours. The UV irradiation was about
half as much (after 30 hours, compared to ammonia at 16 hours). If you are
considering an alternative to ammonia, therefore, it seems UV irradiation is
perhaps a better choice than ethanolamine.
2) Referring to table 3, the data here deal with the effects of various
finish coatings on wood color. The authors don't explain very clearly if
the delta E values related to the patinated cherry are cumulative or
additional changes after the patination. From the text, it seems to be
cumulative, but this is a key point for interpretation. At any rate, I find
it interesting that the color changes associated with putting oil or
oil/varnish on the cherry approach the same as you get from the ethanolamine
fuming. This begs the question, why bother with the ethanolamine fuming at
all? Of course, this color change is still much less dramatic as that
obtained from ammonia fuming.
3) The remaining figures and tables for the most part deal with an attempt
to explain the possible mechanism of the ethanolamine reaction. In my
scientific opinion, these attempts are not very comprehensive or convincing
at all. The FT-IR data is extremely weak in determining a reaction
mechanism for the color change, yet the authors seem to draw a strong
conclusion from this result and in their conclusion actually state that
their data is virtually conclusive. I can guarantee you that further study
would be required to hold muster in a scientific audience. Even more
interestingly, to me anyway, is the fact that they identify the lack of
chemical evidence from their UV irradiated samples (at least from the IR
data), yet these samples had equivalent or greater color changes to the
ethanolamine treated samples. They sort of hand-wave this away and refer to
previous studies, but don't really give satisfactory evidence as to why
their samples don't agree with those other data. Finally, the EPR
experiment was quite a stretch (and the authors fully acknowledge this) as
to discussing a free radical mechanism for the oxidation reaction in the
wood. Using this experiment was actually pretty creative, although their
data was far from actually giving any evidence for their speculations.
Ok, all of this is pretty technical, I'll admit. For the woodworker, I'd
say that you are still going to do one of a few things if you want to try to
artificially age wood (specifically cherry, in this case).
1) Continue to use ammonia fuming. This report gave ample evidence that if
you want dramatic and rapid color changes that ammonia is by far the most
effective way to go.
2) Use UV irradiation. If you are dead set against using ammonia, then
this report showed UV irradiation will give rise to color changes, albeit at
much longer exposure times than with ammonia.
3) Put an oil finish on the wood and let it age naturally (i.e. for about 6
weeks). The initial color change from the oil was about equivalent to the
ethanolamine and/or UV irradiation, and then a further color change of up to
a delta E of 6 was seen after 42 days (figure 4). This is beginning to
approach the results of the ammonia fuming process.
So, there you have it. There are some pretty basic reasons that ammonia is
so effective at this type of oxidative process. When you take the free
ammonia and restrict it chemically by attaching to a carbon (forming a
primary amine, as in ethanolamine), it is not surprising that the reactive
properties associated with the free electrons on the nitrogen atom become
somewhat reduced. In other words, the reason that ammonia is so corrosive
and unpleasant to work with are the same reasons it is good at fuming wood
and if you remove those unpleasant properties you will also reduce the
effectiveness at the wood treatment process.
Not sure if this makes any sense, but I gave it a shot.
There are no stupid questions.
There are a LOT of inquisitive idiots.
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