As the term suggests, “indented” writing is a type of indentation (i.e., physical impression or distortion) in a piece of paper that occurs when writing is produced on one piece of paper while it is resting on another piece (or a pile) of paper. Such indentations or impressions may be visible (i.e., seen with the unaided eye, particularly when they are deep in the paper), but most are ‘latent’ to some degree (i.e., not easily seen or even detected with the unaided eye). Latent indentations, in particular, often provide useful information because the writer is generally unaware of their existence.

Tests have shown that indentations may transfer through multiple sheets of paper positioned beneath the top-most sheet (i.e., the one where the visible writing is being done). In addition, such indentations can be very stable over time lasting weeks, months, or many years. Note that the stability of indentations is dependent upon the substrate material used, and the specific storage conditions.

Indentations may also occur for reasons other than writing by hand. In fact, whenever pressure is applied to the surface of paper it can produce an indentation. For example, paper passing through a printing device often has latent indentations relating to the transport and paper-handling mechanisms.

There are other sources of markings that may look like indentations. Therefore, care must be exercised when interpreting, deciphering, or sourcing indentations.

There are various methods for non-destructive detection and/or decipherment of latent indentations, including side/oblique low-angle lighting or the use of an Electrostatic Detection Device.