How to inspect a stamp for tampering




Essentialy watermark fluid is Petroleum Ether (Benzene), a dangerous and toxic chemical, which has been nuetralized rendering it safe and harmless. There are two ways of obtaining Benzene, one is by getting the 'Safe' version from a stamp supply store. The other is to purchase the lighter fluid Ronosol, sold at most markets. The latter is the unsafe version, you should not let it touch your skin or breath the fumes, I would stay away from using it. Most old stamp hands will tell you to use the cheaper and slower drying Ronosol, but before doing so, read the toxicology on this chemical.


Place the stamp, face down in a black or very dark tray, ideally a small tray so you can use less of that expensive watermark fluid (a small bottle costs $12), or if you plan to watermark a lot of stamps invest in an inexpensive ($2) watermark tray. After laying the stamp face down in the tray, pour enough fluid to wet all the stamp. Watch closely as soon as you do this. If the stamp has a watermark the fluid will expose it, it may look like this:

USPS Watermark
The watermark


If watermark fluid exposes a dark line(s) across all or part of it, then the stamp has a crease or a tear, if there is a dark spot, no matter how small, this is a thin (see below for a explanation of what a 'thin' is). Even the smallest tear or thin will seriously effect the value of a stamp.



A thin is an area of the stamp where the paper is thinner than the rest of the stamp, this is usually the result of a stamp hinge being pulled away from the stamp. Most thins can be detected by holding the stamp up to a light source and looking through the stamp from the back, if there is a lighter area then the stamp has a thin. Alternatively use watermark fluid (see above) for a more thorough examination, a thin will then show as a dark area on the stamp.


The forger will use a couple of badly defective stamps as material to repair a stamp with a small thin or a pinhole. Fibers are scraped from the back of the defective stamp with the edge of razor blade, or a small chunk of the stamp is carefully cut out and then the fibers or cut out piece are placed over the thin of the stamp to be repaired. The substitute paper and the edges of the hole int the stamp are slightly moistened and then carefully hammered into place. When the paper has dried it is sanded with very fine sandpaper for evenness. For effect a little eggwhite, colored to match the paper color of the stamp hardens the paper and the final product will easily fool the expert, nevermind you.The final stage is to regum the stamp thereby making it even more difficult to spot.


The best way to detect a filled thin is by using watermark fluid, the filled thin will show up as a disturbance in the paper. It is almost impossible to mesh the fibers completely. Ultraviolet light is even a better indicator as the paper will appear two different shades. It will look a light stain, but careful examination of the edges of the stain will reveal the handiwork.


Slap a hinge securely on the stamp and hope the buyer does not notice. This is a favorite for common stamps as most folks do not take the trouble check every stamp in a collection they have purchased. I have known dealers to get rid of their thinned classics by putting a hinge over the thin, then spicing up an ordinary collection with these classics.


For the individual stamp just hold it to a bright light, you will see the thin below the hinge. For the collections spiced up with thinned classics, be very careful of a so-so collection where the only good stamps are say a $1 Columbian or a 90¢ Perry. Chances are they are thinned stamps with a hinge in the right place. When you complain to the dealer, they will tell you that they do not take stamps off the page and that is your responsibility. The answer to this is, with classics, yes they should and if they do not accept the return leave negative feedback and let me know, I am going to highlight these dealers. I will need a copy of the listing, a picture of the stamp in the listing, a picture of the stamp as recieved and copies of any email correspondance


You will never really know if a stamp is mint never hinged, you will need some expensive equipment to perform such tasks as spectro-analysis of gum color to be absolutely certain. However there are some tests that can weed out most of those regummed stamps.


- compare to another stamp of that issue, is the color of the gum the same? Does it has the same glossiness? Does the good stamp have gum ridges and the suspect stamp not?
- Does the gum have a dull textured appearance? Genuine gum has some glossiness to it and has a smooth appearance
- Is the gum uneven? If so then chances are its a regummed stamp
- Does the watermark appear impressed to the gum? It should be only visible via strong light or by using watermark fluid
- Does it curl when placed face down on your hand for a few moments? A genuine gum stamp will not curl
- Do the perforations tips feel sharp? On a genuine gum stamp they will be soft.
- Does gum extend into the perforation holes? It should'nt, if there is gum on the edge of the perf holes than it is a regum. When stamps are made, gum is applied before the perforation process. It is very hard for the forger to remove gum from the edges of the perf holes


In some instances a thin is just too large to hide, or there are too many perforations missing, in this case the forger will resort to rebacking a stamp. Not an easy process as it means applying a very thin piece of paper, stiffened and colored with egg white to the back of the stamp and copying the perfs with a reperf machine. If the stamp appears to thick or stiff check to see if it is rebacked. They are easy to spot as the reperforations will never glue themselves perfectly.


I have seen single perfs glued to the back of stamps and pressed into place. Always check the back of a stamp carefully, let the back of the stamp excite you first, then look at the front. It's a common mistake to look at the front first, and be so carried away with enthuasism that you miss the tell tale signs of filled in perfs, regumming and rebacking. Be particularly careful of collections or stamps originating from the Netherlands or Germany as I have found that this is a common source of repaired stamps.



Making a false cancel is not that hard for the forger, making it match a cancel of the period is very hard. There are several problems the forger must overcome. The first being older inks of the period stuck poorly to the canceller, it would be uneven, clump or faint. Todays ink will give a smooth, bright, strong and even spread of the ink, a new cancel will look, well how should I say it, new.

A second problem for the forger is that he can only make one date at at time and one location, most will only do so. Hard to spot, unless you see too rare stamps both with the same date and location.

Cancels are applied to stamps that are more valuable used than mint. A classic example is #39. The are very few used, and almost all of them have a New Orleans Cancel, yet you stamps with Georgia P.O.'s, N.J P.O's and the whole of the USA. Any valuable stamp, such as #39, that is worth more with a cancel absolutely needs a certificate as it is easier to fake a cancel than a stamp. This is also true of unusual color cancels, such as green cancels. A 3¢ 1869 locomotive is worth far more with a green cancel than a poorly centered mint 3¢. This is a forgers paradise because at the time cork cancels were used and cork cancels are easy to make. These require a certificate as well.

Commonly when the cancel is applied it is smudged or just the very tip of the cancel is applied so there is less chance of detection.

Cancels are made to look better by removing the unsightly grease markings on the rim of the cancel. Sometimes part of the cancel is redrawn, this is a particular vice of stamps that are not quite tied to a cover. Stamps that have had their cancels bleached off will almost always end up with a slightly faded appearance, which the crooked dealer will tell you is due to sunlight. Forget buying the faded mint stamp, chances are it once had a cancel.


Does the cancel match the period and the post office? If on cover, does it have the right transit markings and was the rate correct for the destination. Using Robert Seigal's Power Search will probably turn up stamps from the same period and area, then you can compare a certificated genuine example with yours.

Here is a check list for you

  • Is the cancel contemporary for the post office and year?
  • Does the color ink match that used by that post office in that year?
  • Was indeed a color of ink used by that town in that year?
  • If it is an official or newspaper stamp and the cancel is heavy? There is a good chance that it is hiding the word specimen or facsimile, look closely under the ink of the cancel
  • Does the cancel add significantly to the value of the stamp? In that case you must get a certificate.
  • Does the cancel appear to clear or too clean? Then it is probably newer than it portrays itself to be.