Visual Cues and Clues: Cracking the Code of Glass Negatives

Aquarius Plateau. J.K. Hillers at work (as photographer). Local Identifier: 57-PS-809, NAID: 517983. This image is cropped from the original.

When you think of photographic negatives today, perhaps you imagine flexible, plastic-like film. However, some of the earliest negative images would be found on glass. Glass served as a viable support to capture the photographic image on during the early forms of photography. High quality glass was typically selected for its flawless and transparent properties. Earlier on, glass was usually cut by hand, which could result in roughly cut edges or an irregular shape. Later on as the process was further improved upon, glass plates were manufactured by machines on a larger scale. In all cases, glass supports had to be treated, cleaned, and polished so that the emulsion–the image layer–would adhere. A photographic emulsion is a light-sensitive coating found on a support; in this case–on glass. To learn more about early 19th century photographic processes, see our detailed blog post.

While it can be obvious in person that you are viewing a glass negative, there are a few hallmarks or signs to look out for when you’re exploring digitized collections online. Oftentimes–for better or worse–the most obvious markers are the deterioration you see on the image itself.

First, the most obvious sign that you are viewing a glass negative is if you see signs of damage to the glass itself. This can be most seen in cracks in portions of the glass, or fully shattered images. In the image below, you can see the left portion of the photo is unfortunately almost completely shattered glass.

Moveable Dam: Downstream Face of Girders In Place. Local Identifier: 77-SOO-631, NAID: 45711853.

Next, you can notice emulsion deterioration, which can look like crackling or missing portions of the image. The emulsion is the image layer itself, coated on the glass support. Usually you can notice any emulsion deterioration in the corners or edges of the photo. Sometimes you can even notice scratches in the image, which indicates damage to the emulsion. Below you will see a glass plate with portions of the emulsion damaged and flaking at the top and along the right side, which appears as crackling lines in the image. In addition, you can see portions of the emulsion are missing, which looks like parts of the image itself is missing. This is best seen in the black section above the “L” at the top of the photo.

J.L. Appelby. Local Identifier: 24-PA-A-16, NAID: 148952698.
Close up of the cracking emulsion on 24-PA-A-16.

Another interesting marker is information purposely scratched into the emulsion. Because sometimes identifying information could be separated from the image, oftentimes caption information would be etched into the corners of the photo. In addition, the words will usually appear backwards because of how the image/emulsion is adhered on the glass. In the example image below, you can see the words “Gun [Boat] in the James near Aikens Landing” written at the top.

Monitor “Saugus” at Aikens Landing, James River. Local Identifier: 111-B-398, NAID: 524818.
Close up of the written information on 111-B-398. Please note this image has been reversed and cropped from the original.

Lastly, one of the harder to find hallmarks are the fingerprints of the photographers themselves. In the early processes of developing images on glass, occasionally photographs would accidentally touch the developing emulsion. If they touched it at just the right moment, it would leave a fingerprint in the image. While not all glass negatives will have this marker, it is interesting to find in some images. Included below is a photograph that shows extensive damage to the glass in the left corner, as well as the emulsion, which includes two fingerprints in the top right corner.

Hon. Richard C. McCormick. Local Identifier: 111-B-3225, NAID: 527410.
Close up of fingerprints seen on the emulsion layer. Cropped from the original 111-B-3225.

In the Still Picture Branch at the National Archives and Records Administration, we have a large number of glass negatives in our holdings. As we work to digitize our holdings, you will continue to see digitized versions of our glass records in our online catalog. These tips will help you better judge if the images you’re seeing online are glass negatives.

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The photographs included in this post have no known copyright restrictions. If you have any questions about the images in this post or the holdings of the Still Picture Branch, please contact us at


Generally, copies of photographic records held by the National Archives may be published without special permission or additional fees. The National Archives does not grant exclusive or non-exclusive publication privileges. Copies of Federal records, as part of the public domain, are equally available to all. A small percentage of photographs in our holdings are or may be subject to copyright restrictions. The National Archives does not confirm the copyright status of photographs but will provide any information known about said status. It is the user’s responsibility to obtain all necessary clearances. Any use of these items is made at the researcher’s or purchaser’s own risk.

Proper credit lines are encouraged in the interest of good documentation. They also help inform the public about government photographic resources that are available.

*Because so many of our requests for information cite credits and captions that appear in published works, the inclusion of a photo number in hard copy and electronic publications is of great assistance to both us and the public.

Examples of preferred credit lines are as follows:

  • National Archives photo no. 210-G-C241
  • Credit National Archives (photo no. 83-G-41368)
  • Courtesy National Archives, photo no. 83-G-41430
  • National Archives (210-G-A14)

If using a large number of our images, the National Archives will appreciate receiving copies of publications that contain our photographs. Such copies can be sent to the Still Picture Branch or the Library, National Archives and Records Administration.