If you think your clues are non-existent, don't worry. Narrow your search by knowing more about the photograph, i.e., what TYPE of photo is it, when was it TAKEN, who is the PHOTOGRAPHER, what do the CLOTHES look like, what AGE is the person in the photo and what distinctive FACIAL FEATURES are visible? The finished plate was usually mounted in a velvet case or a silk padded wooden case. A coating was applied to the glass plate to hold the silver nitrate on the surface.
Identifying people in old family photos requires some detective work but if you know what to look for and what it means when you find it, you're well on your way. Lists of hallmarks can be found in reference books in the library. This was put against a black background and it appeared as a gray-green positive and is not reflective. Prints from the resulting negative plates were made on very thin paper that had been treated with various mediums.
The process was expensive and it usually tarnished. Hallmarks may be stamped on the back of the plate and can be used to date the photo. It was more convenient than either the wet or collodion dry plate and was in use until about 1920 when it was replaced by the plastic based films available in rolls.
The image can appear as either a negative or a positive depending on the reflective light. The gelatin roll print film was invented in 1884 by George Eastman..
Is there a group picture with somebody in it that you know? A brass mat was used to provide a space between the image and the cover glass. The plate had to be exposed in the camera before it dried, thus the "wet plate" term.
Prints were cut into individual images and mounted on cardstock or on the treated iron of the tintype and were typically 2 ½ x 4 inches.
There is usually a photographer's imprint on the back.. Because of the larger size, they could be touched up.
Photographers also found they could put their name on the front.
Because these prints were mounted on such thin paper, they were glued onto card stock to provide strength.
The card stocks are good clues to dating these photographs.
The Cartes-de-visite were very popular during the Civil War because they could be included in letters aka CDV's.
Multiple portraits were exposed on a single plate that was 6 ½ x 8 ½ inches by using a rotating camera back.