How to check stamps: perforations, watermarks and gum

Perforations

Perforations are measured as the number of holes in 2 cm, using a perforation gauge. Many varieties differ only by perforation, so forgers sometimes add or trim them.

• The perforation count matches the catalogue for the variety claimed
• Holes are even in size and spacing along each side
• Straight edges are genuine sheet edges, not trimmed perforations
• There are no signs of reperforation, such as uneven holes on one side only

Watermarks and paper

Many classic stamps are printed on watermarked paper. A watermark tray or watermark fluid makes it visible without harming the stamp.

• The watermark design and its position match the variety
• The paper type and thickness fit the issue
• On modern stamps, UV light can show coatings and phosphor bands that should be there

Printing method

Under a loupe, the printing method is often clear. Engraved stamps have raised ink you can feel and see; lithographed and photogravure stamps are flat. A forgery of an engraved stamp is often printed flat.

• Lines are sharp and fine where the original was engraved
• Colours and shades match the catalogue
• The design matches genuine examples in every detail

Gum and cancellations

• Original gum has the texture and sheen typical for the issue; regummed stamps often look too shiny or show gum on the tips of the perforations
• Hinge marks lower the value of unused stamps but do not make them fake
• Cancellations on valuable used stamps should be the right type, date and town for the period, with ink that sits naturally on the paper

Expert certificates

For valuable stamps, a certificate from a recognised expert committee or expertising service is the normal standard. Ask for one, check that it matches the stamp exactly, and confirm it with the issuer if in doubt.

Photos to take for a check

1. 1The front of the stamp, flat and evenly lit
2. 2The design and printing, close up
3. 3The back, showing the gum or hinge marks
4. 4Any certificate that comes with it