In the 1920s magazines as an example, black and white photos are usually called illustrations. But some were called engravings. I don't see much difference in them. Does anybody know why some were done as engravings?
Most of the black-and-white pictures in the National Geographic are photographs. Sometimes, however, they would include images using a technique known as photogravure.
Photogravure is an art form in and of itself. It is a photo-mechanical process whereby a copper plate is coated with a light-sensitive gelatin tissue which has been exposed to a film positive, and then etched, resulting in a high-quality intaglio print that can reproduce the detail and continuous tones of a photograph. It registers a wide variety of tones through the transfer of etching ink from an etched copper plate to a special damped paper run through the etching press. The unique tonal range comes from its variable depth of etching, that is, the shadows are etched many times deeper than the highlights.
I hope this helps.
I understand the process. I was just curious as to why they used it or needed to.
The engraving process produces a more detailed image with subtle shading. Photographic copies on the other hand are reproduced in the magazine as a series of dots, with shading determined by dot size. This process limits the detail that can be reproduced.
The downside of engraving is cost. It requires special paper and ink. Also, they generally have a brownish hue (sometimes greenish). Because of the special paper, photogravures are generally full-page, while photographs can be any size, and can be on the same page as text.
Nice picture. Too bad we can't see the same picture both ways side by side for comparison.
Interesting tidbit on Photogravures:
A few years ago, "Les Nus de Drtikol", a folio of 30 photogravures by Frantizek Drtikol was sold at Christies for over $30,000. We are getting ours much cheaper than that, I'd say.