Deterioration of Glass Plate Archives - And How to Avoid it.

The Preservation of Glass Plate Negatives

Collodion glass negatives can develop networks of cracks along the edges of the plate, which may lead to image loss. Glass plate negatives may also exhibit signs of glass deterioration, including a whitish surface haze and/or an efflorescence of viscous droplets.

Glass plate negatives are one of the most beautiful photographic film formats.  Holding such stunning images and historical relevance from family archives to corporate and historical collections.  Our company specialise in the digitisation of this special media.  With age though comes deterioration issues, one that is very important to recognise and understand.  It is important to have photographic film digitised before further damage is caused. See above image of the complete collodion element falling off the negative glass plate.

Given glass plate negative history is so rich in detail, I have prepared a fascinating blog from by Greta Bahnemann https://www.webjunction.org/documents/webjunction/The_Preservation_of_Glass_Plate_Negatives.html

Kind regards

Cheryl

Oxford Duplication Centre

Almost all archives possess some type of photographic collection. Many individuals typically think of “photographs” as plastic-based negatives and slides; but these photographic techniques are relatively recent inventions. Prior to the invention of cellulose nitrate film in 1903, photographic emulsions were made on glass supports. These glass supports are typically referred to as glass plate negatives. 

The term “glass plate negative” refers to two separate formats: the collodion wet plate negative and the gelatin dry plate. Both of these formats consist of a light sensitive emulsion that is fixed to the glass plate base with a binder.

Dozens of photographic techniques have been used within the past 150 years. Each photographic process possesses its own “unique deterioration characteristics” and each process's degradation is accelerated by slightly different factors. 

Almost all archives possess some type of photographic collection. Many individuals typically think of “photographs” as plastic-based negatives and slides; but these photographic techniques are relatively recent inventions. Prior to the invention of cellulose nitrate film in 1903, photographic emulsions were made on glass supports. These glass supports are typically referred to as glass plate negatives. The term “glass plate negative” refers to two separate formats: the collodion wet plate negative and the gelatin dry plate. Both of these formats consist of a light sensitive emulsion that is fixed to the glass plate base with a binder.

Dozens of photographic techniques have been used within the past 150 years. Each photographic process possesses its own “unique deterioration characteristics” and each process's degradation is accelerated by slightly different factors (Northeast Document Conservation Center, 1999, p. 1). Additionally, all photographic processes demand specific storage and exhibition considerations as well as training in the proper handling and care. Glass plate negatives are no exception.

This paper begins with a brief overview of the history of glass plate negatives beginning with their invention in the mid-nineteenth century and their usage through the first quarter of the twentieth century. The paper then explores the storage of glass plate negatives including current research on their ideal physical environment, shelving and the use of enclosures and sink mats. The paper then discusses handling techniques (including retrieval) as well as common conservation concerns including the chemical breakdown of the glass, appropriate ways to deal with broken and cracked glass and the problem of image separation from the glass. The paper concludes with a discussion of the reformatting of glass plate negatives and the use of scanning and digitization as a means to create preservation and user copies.

A Brief History of the Two Photographic Processes

The first photography processes were developed during the first half of the nineteenth century. Between the years 1826 and 1839 three separate individuals – Joseph Nicéphore Niepce, Louis Jacque Mandé Daguerre and William Henry Fox – independently developed the earliest photographic techniques (Vail, 2002, p. 1-2). In 1851 the British inventor Frederick Scott Archer expanded on the discoveries of these early photography pioneers and produced the first wet plate glass plate negative.

The advent of the glass plate negative resulted in an increased interest in photography. The operation of taking a collodion positive on glass consists of the following subdivisions:

1. Preparing the glass plate.
2. Coating the prepared plate with collodion.
3. Sensitizing the plate.
4. Exposing the prepared plate in the camera.
5. Developing the picture.
6. Fixing the image.
7. Drying the plate.
8. Remove any particles which may be settled on the plate.
9. Flow the plate with the “purest and most transparent crystal varnish, precisely in the same manner as the plate was covered with collodion.
10. Apply a dark background to the plate in the form of black velvet or paper.

Frederick Scott Archer's wet plate negative was produced by spreading a glass plate with collodion, a flammable liquid made of cellulose nitrate and ether. The glass plate was then placed into a bath of silver nitrate which turned the collodion into a photosensitive silver iodide. The wet plate was then exposed in a camera. The photographer then had approximately five minutes to complete the exposure before the wet plate dried. The exposed plate was then protected with a coat of varnish. The wet plate negative was in use from the early 1850s until the late 1880s, before being almost completely replaced by the more convenient dry plate negative process.

In 1871, Richard Leach Maddox developed the first practical dry plate negative process. Maddox's technique involved fixing a light-sensitive gelatin emulsion to a glass plate. The plate was then allowed to dry before it was exposed in the camera. The dry plate process featured many of the same steps as the wet plate process but utilized different sensitizing, fixing and development solutions. The dry plate photographic technique was used from the 1870s until the first quarter of the twentieth century, when it was then surpassed in both ease and popularity by the gelatin silver paper negative and the gelatin silver negative on celluloid roll film. 

Storage of Glass Plate Negatives

While the two separate glass plate negative photographic methods are chemically different from each other, they have very similar storage, care and handling needs. The proper storage of glass plate negatives begins with establishing acceptable temperature and relative humidity levels. Cooler temperatures will slow the rate of chemical reactions that cause degradation, but caution should be taken to avoid too low of a temperature which can render the glass, photographic emulsion and binders brittle. The ideal storage environment for glass plate negatives is “less than 65º Fahrenheit with minimal fluctuation (+/- 2 degrees), and an ideal relative humidity is 30% RH with minimal fluctuation (+/-3 percent).

Individual plates should be placed in loosely-fitting buffered paper sleeves or four flap envelopes. After individually enclosing each negative in an envelope, glass plate negatives should be stored vertically along their longest edge and placed into appropriately sized document boxes. 

The storage of broken plates and those with flaking emulsions present added challenges, and additional steps are needed to ensure their protection. Broken plates should be housed in specially constructed protective sink mat enclosures made from corrugated board. Glass plates with significant flaking that includes hanging flaps or tears of emulsion and/or overall cracking of the emulsion should be treated more aggressively. Preservation copies of the images should be created in order to minimize the need to handle the originals and, the flaking plate should then be placed in a sink mat enclosure and stored flat 

Handling Techniques for Glass Plate Negatives

The handling of glass plate negatives should be done with extreme care. Glass plates are most vulnerable to cracking and breaking during the periods in which they are handled. Proper handling techniques begin with a properly prepared work surface. 

Many archivists recommend the wearing of non-vinyl plastic gloves for the handling glass plates. These types of gloves include both Latex and Nitrile gloves. Cotton gloves are not worn as they are too slippery for handling glass and any loose cotton fibers may pose a risk of snagging any flaking emulsion. When working with a plate, always place the emulsion side up. This prevents any debris from scratching the photographic surface.

Preservation Concerns

Glass plate negatives present unique preservation challenges due to their fragile physical format and highly varied chemical structures. Every photographer developed his or her own preferred methods and formulas for the collodion, developers, fixers, post-processing treatments and varnishes.  The deterioration of the glass is often moisture-related. By the early 1990s, the National Archives recognized that many of their plates were undergoing a chemical change on the non-image side of the glass plate. This meant that the glass itself was changing in its chemical structure. The non-image sides of the plates can exhibit a crystalline deposit that is often characterized as being either sticky or slippery. The image side of the glass also exhibits problems with softening as the glass degrades and can exhibit problems with the lifting of the binder and varnish layers. Additionally, the glass plate itself can become increasingly brittle and more prone to cracking and breaking. These changes in the chemical structure of the glass are closely associated with variations in environmental conditions, especially changes in relative humidity levels. The hygroscopic nature of the salts found in the glass can also contribute to the deterioration of the silver image.

The stability of the glass negative's other chemical components can also be problematic. The silver image is subject to oxidative deterioration, which often presents itself in the fading and discoloration of the image. The oxidation of the silver image is often initially caused by poor chemical processing and the use of unstable materials, but the condition is exacerbated by elevated relative humidity levels, atmospheric pollutants and low quality storage enclosures. Collodion, the binder in which the image's silver particles are suspended, can also present preservation concerns. Collodion is composed of cellulose nitrate - a chemical compound that is known to be unstable. The National Archives concluded that while the cellulose nitrate in the collodion is of concern, it is less a factor in deterioration of negatives than the degradation of the glass support.

The stabilization of glass plate negatives is a multi-step process. These steps begin with condition assessment reports and a survey of the plates storage needs. Stabilization continues with the cleaning of the negative, including the removal of any pressure sensitive tape and/or adhesives. This is generally followed by the reformatting and re-housing of the negatives and concludes with the placement of the original negatives into cold storage.

Creating Digital Collections with Glass Plate Negatives

As with many types of archival materials, there is often a conflict between providing public access to glass plate negatives and ensuring their preservation. The most important aspect of glass negative preservation is to ensure the image is retained and made accessible. In order to attain both goals of access and preservation, glass plate negatives should be reformatted. Reformatting creates copy negatives for public access and minimizes the need to view originals which can then be placed into cold storage.

Traditionally glass plate negatives were duplicated by creating contact-prints onto Kodak S0-015 paper combined with the use of Direct Duplicating Film. Today new standards in digital technology have been developed that make the reformatting process easier, faster and more readily available to smaller institutions. The digital reformatting of a collection's glass plate negatives is usually accomplished by scanning the original negatives using both a flat-bed scanner for smaller plates and an overhead capture digital camera (such as a MARC II camera) for larger sized negatives.

One important step in any digitization project is the establishment of image standards and best practices for each type of digital image generated during the reformatting project. The standards for spatial resolution, tonal (pixel depth) resolution and file formats should be established separately for each type of digital image, including online uncompressed archival images, compressed service images, thumbnail images and the master archived image. 

Conclusion

The preservation of glass plate negatives is not without its challenges. A combined response can help ensure their survival. This response includes the creation of appropriate storage conditions, understanding the proper care and handling techniques, awareness of preservation concerns and the importance of reformatting. When these steps are paired with common sense and staff training, the life of a glass plate negative can be prolonged, and generations of users can access and benefit from the negative's informational and evidential values.

by Greta Bahnemann https://www.webjunction.org/documents/webjunction/The_Preservation_of_Glass_Plate_Negatives.html