What Are Glass Negatives?

glass negatives

What Are Glass Negatives?

Glass negatives are negatives on a glass plate. Sounds simple, right?


Today, glass negatives are an interesting relic in photography history, but they were state of the art for the early forms of photography. They were an answer to the paper negative, a medium that created grainy and soft images. Unlike paper, glass allowed for sharper, more detailed photos and helped pave the way for reproductions, faster photography methods, and technology. 

What Are Glass Negatives?

The first generation of glass negatives were unpredictable. There wasn’t a standard formula to creating the plates, and everyone was trying to figure out the best methods. For glass negatives, you need a form of gelatin and silver nitrate for adhesion and expansion. The formula changed depending on the type of photography (i.e. albumen vs. collodion), but those two ingredients were essential for this process. 

There were two different types of glass negatives — wet plates and dry plates. Wet plates were created in the field. Photographers had a portable dark room where they applied their mixture to the plate on location. Dry plates were typically manufactured in a facility and purchased in batches. Dry plates helped standardize photography practices because wet plates had a tendency to be unpredictable in their formulas and application as they were created one-by-one. 

Over the years, photography evolved, and the methods changed in both plate preparation and processing. Exposure lengths shortened, which allowed photographers to photograph people rather than buildings and landscapes only. As technology expanded, processing and printing chemistry matured into many of the common types of photographs we see today including cabinet cards, crayon portraits, and more. Some of the more interesting types include positives on glass.

Positives Rather Than Negatives

A positive is an image where the dark to light ratio is the same as the subject in the photograph. A negative is the reverse. In a negative, light appears dark and vice versa. There have been times when a client brings in an image on glass and is convinced it is a negative when it is really a positive. 

One of the most common positives on glass is the ambrotype, but there are other types. There are monochrome transparencies that are displayed through light, color positives, and more. We have had clients bring in positives that have been hand colored, and they are interesting pieces of art. Don’t assume that you have a glass negatives until you accurately assess the images you have. 

Common Damage and Preservation

Images on glass, whether they are positives or negatives, are sensitive to oxidation, delamination, scratches, abrasions, and breakage. These pieces need to be handled with care. Avoid touching the surface of the emulsion as oils from your fingers will cause silvering and accelerate deterioration. 

Glass plates can be digitized and reproduced as well as being cleaned and preserved, even if they are broken. We recommend hiring a professional to clean and digitize your negatives. These pieces can only be cleaned on the glass side, not the emulsion side, and it is too easy to confuse the sides if you aren’t familiar with the format. Glass is extremely delicate and should not be left to chance. 

As with most forms of photography, glass negatives should be stored in a stable environment. Extreme fluctuations in humidity will cause the piece to expand and contract which will result in crazing. The Library of Congress recommends keeping humidity levels between 30% – 50% for mixed storage of photographs, negatives, and slides, but notes that glass plate negatives should be stored at 30% – 40% as they can further deteriorate at 40% – 50%. 

There are superior products for storage. Many people leave their glass negatives in the original box that came with the plates, but they should be stored in an archival box with a four flap enclosure. University Products notes that glass negatives should be placed emulsion side down in the enclosure. 

Glass negatives are a treasured piece of photography history. To learn more about the different types of photography, visit Getting Started: Photo Restoration.