SF-05
Latent image
A device hidden in the direction of engraved lines, visible only when the sheet is tilted to a raking light.
Latent image ×25
Specification
- House code
- SF-05
- Method
- Directional engraved line structure
- Apparent at
- ×25
- Deters
- Copying by any process that records the image from one angle only.
- The recipient’s check
- Hold the document flat at eye level and tilt it slowly toward a light. A word or device that was not there a moment ago appears, then disappears again as you tilt back.
Two areas of a plate can be engraved to exactly the same ink density and still behave completely differently, if the lines run in different directions. Viewed square-on, both look like flat tone. Viewed at a shallow angle, the ridges of one catch the light while the ridges of the other shadow — and a device that was invisible resolves out of the tone.
The image is latent in the strict sense: it is present in the plate at all times and only the viewing geometry decides whether you can see it. Nothing is added and nothing changes.
What it is for
A latent image is the feature to specify when a document will be checked by someone with thirty seconds, no equipment and no training. It requires only that they tilt the sheet, and the answer is unambiguous. It is correspondingly demanding to originate, since it depends on the relief of the engraving rather than on its appearance, and only intaglio produces relief of the necessary depth.