What Do I Look For When Using A Short Wave UV Light Looking For Tagging?

Sorry but I hope this is the correct area to post this question. I just bought a Short Wave UV Light to look for tagging on my US Stamps. The problem is that I do not know what to look for. Every stamp I look at my sheets it looks the same with or without the light. What could I be missing? Does it work if the stamp is in a glassine envelope? Or mounted in an album with the plastic covering (crystal mount I think it is called? Or does the stamp need to be without any covering? Any help is greatly appreciated.
Robert

*** Moved by Staff to a more appropriate forum. ***

In order to see a difference, the stamp has to be tagged. It shows up as a bluish or greenish glow and usually best seen in a darkened room.

Tagging did not start until the mid-60's. Most lower value stamp are not tagged and presort bulk rate stamps are not tagged.

Example:

Sorry no help on the light question but a word of caution.
If the mounts are in fact "Crystal Mounts" they can damage your stamps

I bought a very cheap uv light and can't see a thing with it. Doesn't it have to be a certain wavelength, different for different countries? Also, how dark must the room be? Is it impossible in tghe daytime without blackout drapes?

Don

In my somewhat limited experience the "glow" is often hard to see, even in a dark room, unless you know what you are looking at. (It certainly is not always as noticeable as in the example that Angore posted.) The best way to learn to "see" tagging is to compare side by side two versions of the same stamp, one which you know is tagged and the other which you know is not. Once you've seen what a tagged stamp looks like in relation to an untagged stamp, then it gets a little easier.

It may be that my experience is somewhat atypical since it is limited primarily to stamps tagged during the early years of tagging. Maybe more recent stamps reveal the tagging like Angore's example.

Yes, a lamp needs to be filtered for a specific frequency. If it is too general (broad spectrum light), it can mute the effect. They cannot be in mounts since that blocks UV. The cheaper lights are low power but a slightly dark room should be sufficient. Find a sure thing -- a modern US first class definitive.

Also be forewarned that tagged US airmail stamps issued prior to 1980 used a different tagging chemical which glows a soft orange red under short UV. The orange red is not as obvious to the casual observer as the yellow or blue green tagging. Starting with the Philip Mazzei issue in 1980, airmail stamps were tagged in the same manner as other US stamps.
Added: A stamp being examined via UV must not be enclosed in a glassine envelope or a mount. I.e., you need to avoid enclosing the stamp in something that would block the UV. An example of something that, in my experience, does not block the UV is the cellophane used by the USPS to wrap their stamp products.

JLLebbert,

Your explanation about the difference with US airmail stamps before 1980 explains the experience I was describing, especially with respect to stamps in airmail booklets. Thanks for pointing this out.

Basil

Thanks for the help everyone. I did get a light off ebay. I tried it on several full sheets in a poorly lit room and it was real easy to see the tagging on the US Postal issue of the late 1970's(?), early 1980's(?) and one or two other issues. All of the others are very hard to distinguish anything so I am still unsure of those. They are probably tagged since the catalog value is around $75.00 untagged and I could not get that lucky, but who knows....maybe? Again, thanks for the advice and help everyone. I have a lot to learn.
Robert

I have found that short wave UV will not penetrate stamp mounts (Scott mounts are what I use), whereas long wave UV will. I don't recall the effect when the stamp is in a Vario page.

Robert

Thanks. I am not trying through the mounts. I am only using it directly on the stamp.
Thanks again,
Robert