Watermarks are secret marks in paper that are difficult to detect with the naked eye. They were used by the US Postal service on some stamps between the years 1895 to 1916.

The watermarks are in the form of letters. U,S,P and S embossed across the sheets of paper that were used to make multiple stamps. And depending on where they were put on whole sheets of stamps they could show up anywhere on the back of a stamp. Sometimes a stamp will have a whole letter on it and sometimes it will have a partial letter.

There are a lot of different stamps out there! And there are a lot of stamps that look exactly the same but arent the same exact stamp. They were issued in different years. And finding the watermark on these stamps, or lack of watermark can help us better identify exactly what stamp it is.

This tutorial shows you how to check for the watermark in a stamp.

To do this we need some watermarking fluid, a tray to hold the fluid and a pair of tongs.

We are going to soak this stamp to check out the watermark on the back. This is a 1 cent Franklin stamp. (Scott #279). It was issued in 1898.

Place the stamp face down on the tray. At this point, with a nice black background you might be able to see the watermark! If so then there is no need to use the watermarking fluid. But if you can't see a watermark then go ahead...

Note that I am using an actual watermark tray that I bought for five dollars. You can use just about any kind of a black tray for this. It is important that you use a black tray though. It helps in seeing the watermark.

Slowly add some watermarking fluid. The watermark comes right out. It is very clear on this stamp. It is a double Line "U".

Let's take a look at a few more.

Now I am soaking some more stamps to see if watermarks come out. In this batch of five there are three that show clear watermarks. the one on the upper left is another double line U. The one on the upper right shows a single line S. And the one on the lower right shows a single line U. Kind of cool.

About the Single and Double line watermarks. This graphic gives you an idea of what they are. The top one is double line and the bottom one is single line. This isn't the same exact font used by the USPS but it give you an idea of the difference between the two.

Knowing the difference helps in identifying what stamp you are examining.

Some stamps that were issued between 1910 and 1916 have the single line watermark. By single line I mean that the letters are written with a single solid line.

Watermark Detecting Fluid

Safe for detecting watermarks on most stamps. Will also remove self-stick stamps and tape from paper. (Benzine free)