Philatelic expertisation is the process whereby an authority is asked to give an opinion whether a philatelic item is genuine and whether it has been repaired or altered in any way. Forging and faking, regumming and reperforating of stamps is common in the philatelic marketplace, and increasingly buyers demand an expert certificate before buying a valuable item. Some items are so often faked or altered that they may be almost unsaleable without a certificate.

The process of expertisation

Experts may be individuals or committees but they will all follow a similar process to determine whether an item is genuine. The opinions of experts differ and have evolved over time. Conflicting expert opinions, such as on colour shade or whether a stamp has been reperforated, can have a huge effect on a stamp's value.

Stamps

Experts will attempt to determine whether a questioned stamp is a genuine example of a particular stamp issue; that is, whether it was printed at the same time from the same plate or stone as that stamp issue. Among the factors they may consider are: Experts also will ask whether the stamp been altered in any fashion: Experts will also attempt to determine whether genuine stamps have been repaired or cleaned:

Covers

Among the factors experts may consider for a cover are:

The tools of expertisation

Experts will often maintain their own library of fakes and forgeries, and they also have access to the records of past genuine items that they have seen. They will usually have a large library of philatelic literature to refer to. Scientific equipment is essential, including: Common sense and above all, experience, are also vital.

Expert certificates and marks

Once an item has been examined, the expert(s) will issue a certificate giving their findings which will include identification, genuineness or otherwise and comments about any alterations or unusual features. The certificate will normally feature a photograph of the item and be signed. It may also be embossed or have other security features. In the past it was common for experts to sign or add their mark to the back of stamps, however, this is nowadays uncommon as it is by some regarded as an undesired alteration. In Germany (BPP) it is still common practise to sign many items, but generally not the most valuable. There have been instances where expert certificates have themselves been faked and in the "Blüm Case", a forger produced false expertizing marks that were applied to German colony stamps and others.

Finding experts

In the United States, the Philatelic Foundation, American Philatelic Society and numerous specialized stamp collecting organizations have committees who will perform expertisation for a fee. In Great Britain The Royal Philatelic Society London has a renowned expert committee which is also the oldest in the world, and of equal fame is the BPA expert committee. German experts usually belong to the Bund Philatelistischer Prüfer (BPP). Specialized in their countries issues are e.g. the expert committees of NVPH (Netherlands), COMEX (Spain), Isphila (Turkey).

• In addition, the International Association of Philatelic Experts (AIEP) is a worldwide organisation for independent stamp experts. The results of expertisation may be challenged, and in some cases further research has shown the genuineness of an item considered a forgery, or vice versa.