Material Chronometry
A signature is only as valid as the material it resides upon. Chronometry is the definitive exclusionary tool. If George Washington signed a document using a Sharpie, you don't need to analyze the handwriting.
Optical Brightening Agents (OBAs)
Prior to roughly 1950, paper was not treated with modern chemical brighteners. In the late 1940s and early 1950s, manufacturers began adding OBAs to paper to make it appear whiter by absorbing UV light and re-emitting it in the blue region of the visible spectrum.
The Rule: If you are evaluating a signature purportedly signed on a photo or document prior to 1950, and the paper aggressively fluoresces bright blue-white under a 365nm UV light, the item is an anachronism. It is a fake.
Ink Introduction Timeline
| Ink / Pen Type | Introduction / Commercialization | Authentication Implication |
|---|---|---|
| Iron Gall Ink | Antiquity to early 20th Century | Standard for historical docs. Corrodes paper over time. |
| Ballpoint Pen (Biro) | Commercialized 1945 | Any ballpoint signature pre-1945 is highly suspect. |
| Felt Tip (e.g., Sharpie) | Commercialized 1964 | Any Sharpie signature pre-1964 is a forgery. |
| Gel Pen | Invented 1984 (Sakura) | Common modern marker. |
UV Light Database
Check our database for expected UV reactions for specific photo papers and document types by decade.
Open UV Guide