Some watermarks will show up if the stamp is laid, dry, on a black surface--some Great Britain and British Empire, for instance. But many, if not most, can only be seen when the stamp is wet (while soaking in water to remove hinges or paper adhesion or, better, when wetted with lighter fluid or commercial watermark fluid). A number of threads on SCF deal with watermark fluids and techniques of detecting watermarks, hazards etc.
And there's this from Linn's Stamp News
http://linnsonline.com/howto/refres...rcourse.aspxhttps://goscf.com/t/9140&SearchTerm...ermark+fluidDipping in fluid (lighter fluid or commercial wmk fluid) also helps reveal hidden flaws. It does not affect the gum, whereas, of course, soaking in water does remove the gum and thus can't be used on mint stamps.
I think it's safe to say that most people on SCF prefer to use lighter fluid because it's much cheaper than commercial watermark fluid. Other factors apply--look at some of the SCF threads on the topic for the details. Obviously watermarking has to be done in a well-ventilated place.
Some USA watermarks are simply very hard to detect even using fluid.
In addition, an individual stamp may come from a specific place on a watermarked sheet of stamps that has no watermark. Hinges and hinge adhesive or paper adhesions all can block the visibility of watermarks even in watermark fluid. Sometimes heavy cancellations obscure the watermark.
In other words, while under the best of circumstances some watermarks are visible when the stamp is dry and placed upside down on a black surface, any of the above-mentioned obstructions render the watermark invisible when the stamp is dry and may make it difficult or impossible to detect even in fluid.
Posted 10/11/2014 07:33 am
