Editing Watermark (section)

== On postage stamps ==
{{See also|Postage stamp paper}}
[[File:Watermark Crown CA.jpg|thumbnail|right|The ''Crown CA'' watermark found on many British Commonwealth stamps (seen from the reverse)]]
[[File:FawnEnvelope1883Plimpton.jpg|right|thumb|A US postal stationery envelope from 1883 showing a clear watermark on [[laid paper]]]]

In [[philately]], the watermark is a key feature of a stamp, and often constitutes the difference between a common and a rare stamp.  Collectors who encounter two otherwise identical stamps with different watermarks consider each stamp to be a separate identifiable issue.<ref>{{cite web|url=http://www.linns.com/howto/refresher/watermark_20051010/refreshercourse.aspx|title=Miller, Rick; ''Stamp identification often lurks in watermark'' in Linns.com Refresher Course section|access-date=2010-12-08|archive-date=2010-06-16|archive-url=https://web.archive.org/web/20100616075435/http://www.linns.com/howto/refresher/watermark_20051010/refreshercourse.aspx|url-status=dead}}</ref>  The "classic" stamp watermark is a small crown or other national symbol, appearing either once on each stamp or a continuous pattern. Watermarks were nearly universal on stamps in the 19th and early 20th centuries, but generally fell out of use, but some countries continue to use them.<ref name=Baadke>{{cite web |url=https://www.linns.com/news/postal-updates-page/stamp-collecting-basics/1998/october/how-to-identify-a-stamp-by-its-watermark-.html|title=Baadke, Michael; ''How to identify a stamp by its watermark'' in Linns.com Refresher Course section }}</ref>

Some types of [[Embossing (paper)|embossing]], such as that used to make the "cross on oval" design on early stamps of [[Switzerland]], resemble a watermark in that the paper is thinner, but can be distinguished by having sharper edges than is usual for a normal watermark.  Stamp paper watermarks also show various designs, letters, numbers and pictorial elements.

The process of bringing out the stamp watermark is fairly simple.  Sometimes a watermark in stamp paper can be seen just by looking at the unprinted back side of a stamp.  More often, the collector must use a few basic items to get a good look at the watermark.  For example, watermark fluid may be applied to the back of a stamp to temporarily reveal the watermark.<ref name=Baadke />

Even using the simple watermarking method described, it can be difficult to distinguish some watermarks.  Watermarks on stamps printed in yellow and orange can be particularly difficult to see.  A few mechanical devices are also used by collectors to detect watermarks on stamps such as the Morley-Bright watermark detector and the more expensive [[Safe Signoscope]].<ref>{{Cite web |title=Signoscope Watermark Detector T3 |url=https://www.safepub.com/product/signoscope-watermark-detector-t3/?srsltid=AfmBOooCj0HG3DezFBXSClHwFT_Nj7H-2pYKqWT_fZjJpVOJHjjUNKX7 |access-date=2024-09-30 |website=SAFE Collecting Supplies |language=en-US}}</ref> Such devices can be very useful for they can be used without the application of watermark fluid and also allow the collector to look at the watermark for a longer period of time to more easily detect the watermark.