A large collection of photos from the 19th and early 20th century is fraught with faces of doom and gloom — and occasionally a literal dead face. There are several theories for why people in early photographs were so solemn in front of a camera. One has to do with the camera itself.

Daguerreotype — the first commercially successful photographic process invented by Louis Daguerre in 1839 — had long exposure times. Moving objects were rendered blurry or not captured at all because of the time it took to record an image on a sheet of silver-plated copper. In portraiture, most thought it would be easier to hold a somber expression rather than a smile during the exposure time.

Watch the video above to learn more about why most early portraits were all business and no smiles.