There are many ways to detect the presence of a watermark:
dipping the stamp in water, lighter fluid (of which RonsonolTM
brand seems to be a favorite), or any of the new
"commercial" fluids prepared for the express purpose of detecting watermarks
(ClarityTM comes to mind). Of course simply holding
the stamp to a bright light source at various angles may be all
that is necessary.
Years ago, before it was found to be a carcinogen, benzene was the
dipping fluid of choice. Today, the use of this dangerous solvent
would be, if not illegal, certainly very foolish, especially since
cheap alternatives are available, chief among them lighter fluid. This is why lighter fluid has become a mainstay in any serious
philatelists hands. Lighter fluid is cheap and, for the most part,
effective and safe. There are a few stamps whose ink will
bleed in lighter fluid (this is not the case for any of the Washington Franklins – for
which lighter fluid is perfectly safe). We have not seen
any increase in detection ability using the far more expensive
commercial watermark fluids, certainly not with the Washington
Franklin stamps. The debate is out on whether lighter fluid leaves
a filmy residue on the stamp. It is certain that dipping a dirty
stamp in lighter fluid often has a cleansing effect, leading to
another debate as to whether this "cleansing"
constitutes a restoration or even an alteration of the stamp. Such
cleansing in the coin world often devalues a collectible coin
considerably. This is not an issue as yet in the stamp world and,
frankly, we feel it never will be. However, the collector should
be aware of this issue and consider it before making any attempts
to "clean" a stamp. All-in-all lighter fluid is
the first choice of most experienced philatelists.
Lighter fluid does have its detractors, however. It is highly
flammable, has an unpleasant odor, and should be used sparingly in
enclosed spaces. Commercial watermark detection fluids have the advantage of
drying more quickly, are not flammable, do not have an unpleasant
odor, can be used in enclosed spaces, and are safe for most, if
not all, fugitive inks.
We would argue that faster drying time is a disadvantage, since it
shortens the critical moment when the stamp first becomes wet and
the critical moment when the stamp is just about to dry, times
when the watermark often comes miraculously into view. In our opinion,
commercial watermark detection fluids do NOT make the
watermark stand out more clearly against the stamp, and should not
be purchased for the added rsolution they might provide.
In fact, we have found that many of the difficult Washington
Franklin single-line watermarks barely perceptible using lighter
fluid, were totally imperceptible using the commercial watermark
fluid, due to the faster drying time. Again, this is merely the opinion of this author, the
reader is welcome to perform their own trials, but we must admit
our disappointment with one of the commercial watermark fluids
that did not live up to its namesake. We were quite pleased with
its ease of use and lack of odor and fumes, however.