A blind impression is an inkless impression. In other words, it occurs when you run the press with an un-inked plate. Instead of color, you see an image simply through texture and shadow created by the impression in the paper.
Oftentimes, we’ll choose to use a gloss varnish or a transparent white ink to amplify the contrast and legibility of the imprint. Though technically no longer inkless, the varnish or tint catches more light and heightens the effect of a true blind impression. Similarly, another option is to run an extremely light tint of a color or, more accurately, a “dirty" tint.
(image: example of blind impression on a wedding invitation)
It is important not to confuse a blind letterpress impression with a blind deboss. Though done on the same machines, the impression created by letterpress printing is incorrectly referred to as a deboss by many people. While (contemporary) letterpress printing does impress the text or image into the paper, the impression is essentially single-sided. There may be some minor bruising or show-through on the backside of the sheet but the intent is not to have a perfectly mirrored image of the print on the opposite side.
With debossing, the image is impressed into the paper by a two-piece die that essentially molds the paper from both sides. There is a raised “male” die and recessed “female” die which together form a crisp, three-dimensional image. To see what I mean, Publicide has some great images that show both sides of a deboss here. Embossing is the same process as debossing, but the final image is raised rather than impressed. Like letterpress, embossing and debossing can both be done blind (inkless).
To recap: a blind impression of any sort is an impression without ink. Being single sided, it is different than a blind deboss. Something to note is that a blind impression is priced the same as if you were using an ink because it requires its own press setup.
Do you have any letterpress-related questions for George? Please email him at info[AT]smudgeink.com!