5 replies to this topic

[nfoto]

This is an excerpt of a hand-written letter sent from England to neutral Sweden in the beginning of 1944, during World War II. At war time, all letters were heavily censored by British military authorities. They either cut out parts of the text, or with air mail written on flimsy light-weight paper such as this letter, they used heavy ink to obscure information deemed to have military significance.

Over the decades since the war ended, the writing in this document has become smeared and difficult to read because the original ink has diffused into the film-like paper substrate. Thus the characters have become blurred over time. The over-inked parts are by now, over 60 years later, solid black and impossible to read by any usual means. Even infrared photography does not penetrate to show any of the censored text.

However, a capture by reflective ultraviolet photography cleans up the handwriting remarkably well and makes the censored parts of the text re-appear.


Image reference: A05100875646_UV_VIS.jpg
Upper panel: Visible light capture, filter Baader UV/IR Cut. in daylight.
Lower panel: Ultraviolet light, Hoya U-360, open shade.

Captured with Nikon D1 (broad spectrum) and UV-Nikkor 105 mm f/4.5 lens.

[Published 14 Apr 2013]

[Akira]

This is a great find! When did you shoot the image? The co-existence of Baader UV/IR-cut and U-360 confuses my sense of time. Another qustion would be if UV and IR worked hand in hand to reveal the sensored part, as the broadband D1 should be quite sensitive to the IR leak of U-360.

[nfoto]

Akira: this document belongs to a family member. She has a large collection of them but many were in such poor shape they might break when handled for photographic purposes.

I tried with pure IR first, using the usual IR filters and IR flash, and that netted me nothing different from the visible-light appearance of the document. With UV the censored text became readable, though. I did take the UV capture in open shade so as to minimise any IR impact.

Currently I have access to the document so might test other spectral bands or filter techniques. If time permits, that is.

[Akira]

Thanks for the detail. May I ask what was written in the cencored part in the letter above? I don't think it is a private topic, because the British army thought it of military significance...

[nfoto]

Basically, the censored parts revealed details about troop movements. Several geographical locations were mentioned.

[Akira]

I see. Then there's enough reason to censor. Thank you for taking your time!