Restauration des plaques de verre du fonds J. Chamonard

Chamonard’s work and technique

The prominent French archaeologist Joseph Chamonard began his collaboration with the French School in Athens (FSA) in 1890. He participated in excavations in Caria and Delos and became secretary of the French School from 1908 to 1912. After his tenure, he continued tirelessly his invaluable archaeological work. His career ended in Syria where he founded the Department of Antiquities. He died in 1936 in Giѐres.

This study focuses on 315 glass plates retrieved from Chamonard’s archive which was donated by his descendants to the FSA at the end of 2019. The FSA, recognizing the importance of preservation and posterity of Chamonard’s valuable records, conducted a conservation project on his work.

Along with his archaeological work, Chamonard took photographs himself as other archaeologists of his time did. Since the introduction of photography in the 19th century, archaeologists recognized the potential of the medium to permanently record their scientific work and to disseminate research ideas. Archaeologists were interested in photographing the pre-excavated site, any relationships between the site and the surrounding landscape, site features and standing structures, artifacts, spatial association between artifacts, trench stratigraphy and excavation layers, field survey finds etc. It was critical for archaeologists to create the best possible image archive not only for their own research but for future generations as well.

In this context, Chamonard used photography to document aspects of the excavations he participated in; extensive views of the archaeological site of Delos and details of various frescos, mosaiques and ruins. He also focused his lens on subjects outside his field of work – but still of archaeological interest – such as the Acropolis with the Parthenon, the temple of Nice and the Caryatids. Moreover he turned his lens to general views of the city of Athens from the Acropolis, views of Mykonos and the Aegean Sea. It appears that photography was a medium that attracted his interest sincerely, since he not only used it out of necessity and as a documentary tool for his scientific work but also for his own distraction.

Chamonard’s genuine interest and knowledge of photography were evident considering the restraints of his photographic equipment and the variety of the photographic materials he used. He recorded his images on light-weight flexible film but his perseverance to continue using glass plates was far from accidental. He defied the strain to carry around heavy glass plates in rugged archaeological sites along with the high risk of breaking them. Glass presented dimensional stability under all environmental conditions and endurance to the successive chemical processing stages, making it a fine support medium. Additionally glass plates produced images of high quality, and as with medium and large format cameras, were and still are ideal in archaeology because of the level of detail and image enlargement obtained.

Finally, the cameras used for stereo photography were bearing two lenses. The most convenient ones for traveling were folding cameras. Depending on the model the stereoscopic partition could be quickly removed and the lens replaced to capture single shot images. Chamonard’s family also donated to the FSA a mahogany Sanderson folding camera (fig. 1) with a single Darlot lens. Sanderson cameras, patented in 1895, were primarily manufactured for architectural projects that required special camera movements. Therefore this camera appears to be the appropriate one for documenting archaeological sites as well and it is highly possible that Chamonard used it to capture the images studied in this project.

Chamonard’s glass plates

The part of Chamonard’s photographic archive that has undergone treatment consisted of 315 images on glass support produced with different techniques; Autochromes, Diapositives, Stereoscopic views and glass plate negatives. According to their materiality they were dated from the early 20^th century. The items were received in original boxes of that era that were used when glass plates were purchased unexposed and ready for use. In many cases the content didn’t correspond to the description of the labeling on the box. Some boxes contained more glass items than they could fit and others had glass plates with a variety of dimensions.

Process	Dimensions in cm	Number of plates
Autochrome	9 x 12 & 13 x 18	70 & 6
Diapositives	8,5 x 10	60
Stereoscopic views (negative)	7 x 15	137
Stereoscopic views (positive)	4,3 x 10,5	12
Gelatin glass plate negatives	10 x 15	30

The Autochrome process

It was just the turn of the century in 1903 when this unique technique was invented by Louis Lumière. In 1904 the invention was patented by Lumière Brothers and industrial production started in 1907 and ended in 1935. Chamonard used this unique medium to take his own Autochrome pictures of the Delos site and to captivate in colour the beauty of the Parthenon and its surroundings.

Autochrome plates are an early type of colour transparencies (fig. 2). In the Autochrome system a varnished glass plate was coated with a layer of minute (0.015mm) potato starch grains dyed with the additive primaries (orange-red, green and violet) in a random distribution of color. The spaces in between the grains were filled by powdered charcoal or a fine black pigment and superimposed over a light sensitive silver-gelatin panchromatic emulsion. During exposure of the plate in the camera, the starch grains act as filters of different wavelengths of light before it reaches the silver-gelatin emulsion. Then the plate would be developed, washed and chemically treated to bleach out the negative silver-based image. Afterwards the plate would be exposed for a second time to light, thus creating a positive silver-based image, redeveloped, washed and sometimes varnished again. When viewed through transmitted light, the dyed starch grains give the image a coloured appearance in the mid and highlight areas. To protect the image, another plate of glass of equal size would have been affixed to the image. Though expensive, the Autochrome system was relatively easy to use and achieved significant popularity despite requiring exposure 50 times longer than the black and white materials of that period. Autochromes are the forerunner of Kodachrome slides.

Diapositives

Diapositives were black and white positive photographic images on clear glass meant for viewing through transmitted light (fig. 3). Most positive transparencies from the 19th century were made from a negative by either intimate or near contact or by rephotographing the negative illuminated from behind. In the 20th century, the negative image was reversed to produce a positive one with further chemical process. The fragile finished image was protected, the image layer was covered with a second same-sized piece of glass and their edges were taped together with black paper tapes. Additionally this format allowed them to be projected by a slide projector for home entertainment and, as in the case of Chamonard, enabling researchers to present their scientific work in large audiences in amphitheaters. In Chamonard’s archive, some Diapositives didn’t have a cover glass. Instead they had black paper tapes adhered on the image layer creating a “new frame”, probably designating the area of greatest interest to the researcher.

Stereoscopic views

Attempts have been made since early days of photography to make photographs more realistic through the use of stereoscopic vision. A stereoscopic glass plate consisted of a pair of photographic images on a single support that when viewed through a stereoscope gave the appearance of a single image having relief and solidity, otherwise a 3D view. The images were not identical but exhibited a slight lateral shift. Having been made with a dual-lens camera and the centres of the lenses being set the same distance apart as the centres of two human eyes, they produced an image of what one eye would see. Therefore, when viewed through the stereoscope, the two combined images resemble human binocular vision conveying the illusion of depth.

Stereoscopic views served the same purpose as Diapositives as they were transparencies for projection and for the illustration of public lectures but additionally offering the visual effect of the third dimension. Chamonard used this technique as he recognized that three-dimension images were important for revealing the details and all the information of an artifact. In his archive there are positive as well as negative stereoscopic views.

Gelatin glass plate negatives

Gelatin glass plate negatives are glass plates coated with a mixture of gelatine and light-sensitive silver halide salts. Glass is a fine support medium since it is stable under all environmental conditions and impervious to chemicals during the development process. However due to their weight, volume and brittleness, glass plate negatives present several disadvantages regarding their safe moving and storage. Richard Leach Maddox began experimenting with glass plate negatives in 1871. They came into mass production c. 1880 and were in common use until the late 1920s.

Condition of reception

Autochrome plates

In general, Autochromes are fragile and sensitive materials to treat. As mentioned before due to their fragility, the light-sensitive glass plate is covered by a supporting glass plate of the same size to protect the sensitive image. Their image surface is prone to abrasion by contact and to delamination from its glass support. In the Chamonard archive, poor storage conditions resulted in numerous cases of protective glass missing or broken. The binding black paper tapes holding the image plate and the cover glass together, had lost their adhesion in almost all cases. As a result, they were either missing, partially detached or had left adhesive residues. Unfortunately, at some point in the past, someone observed this and replaced the original tapes with inappropriate commercial tape. In time, this type of tape became yellow and extremely sticky (fig. 4). Moreover, its adhesive penetrated between the cover glass and the image plate. This fact made their removal -apart from imperative- very demanding, especially in the cases of broken glass plates where commercial tape was used extensively in order to withhold the broken parts.

In the cases where the image was not properly protected by the cover glass, the image layer was delaminated, especially around the edges. Moreover, the plates were exposed to high humidity levels creating irreversible damage to the autochrome image layer. This was observed by a greener overall appearance and the formation of green stains caused by the solubilization of the dyes present in the green filters (fig. 5).

The lack of adhesion and the missing black tapes affected the image layer which came in contact with the oxygen of the atmosphere therefore causing the oxidation of the silver particles of the image. This is known as silver mirroring and it appears as a bluish metallic sheen in reflected light. Finally, the Autochromes had deposits of dust on both glass sides and due to inappropriate handling stains, fingerprints and abrasions (fig. 6).

Diapositives and Stereoscopic views

The Diapositives (positive images) and Stereoscopic views (positive and negative images) of the Chamonard archive were glass plates coated with a mixture of gelatine and light-sensitive silver halide salts. Since both served the same purpose as Autochromes (transparencies for projection), they had many resemblances in their structure and consequently in the damages which were described in detail above. Their emulsion was not as fragile as the Autochromes and most of the time they had a supporting glass plate to cover the light-sensitive image as well, which in some cases was either missing or broken. The two glass parts were held together with black paper tapes along the edges presenting lack of adhesion, detachment and adhesive residues. The missing original tapes were replaced with poor quality commercial tape, becoming extremely sticky in time. It was used extensively to withhold the broken pieces in the cases of breakage, with its adhesive penetrating through the cracks and creating further damage like stains on the light-sensitive emulsion layer. Furthermore, the contact of the unprotected image layer with the oxygen of the atmosphere caused the formation of silver mirroring on its surface. Due to poor storage conditions and inappropriate handling they also had stains, fingerprints and abrasions. Finally, both Diapositives and Stereoscopic views had deposits of dust and dirt either on both glass sides or on one glass side and the image layer.

Dry silver gelatin glass plate negatives

The dry silver gelatin glass plate negatives consisted solely of the image layer and the glass support. As mentioned, they were more stable and less fragile than Autochromes but they had degraded over time. The most common defect was silver mirroring as explained above. Inappropriate handling and poor storage conditions caused the image layer to detach from its glass support and loss of image parts. Moreover scratches, fingerprints, stains, deposits of dust and dirt were usual damage of both the light-sensitive emulsion and the glass support. Finally, a few glass plate negatives were broken and bound together with inappropriate commercial tape. As mentioned above, it became extremely sticky and while withholding the broken pieces, the tape adhesive penetrated through the cracks creating further damages, like stains on the light-sensitive emulsion layer.

Conservation Treatments

The conservation approach was almost the same to all items regardless of their photographic technique. Diapositives, Stereoscopic views and glass plate negatives were coated with the same type of emulsion, a mixture of gelatine and light-sensitive silver halide salts, which is more durable than the autochromic emulsion. Therefore, the conservation treatments differentiated mainly in the cleaning of their image surfaces.

More specifically, the first conservation treatment for all items was surface cleaning and the removal of dust particles and dirt deposits. In the cases of Autochromes where the cover glass was missing and the image layer was exposed to environmental pollutants, surface cleaning of the emulsion was performed with an air bulb due to its sensitivity to abrasion by contact. Therefore, any cleaning with a brush or cotton was avoided. For the rest of the glass plates, the uncovered emulsion layer was cleaned with a very soft brush. All glass covers and surfaces were cleaned with an ethanol and water solution, carefully applied with lightly dampened cotton swabs and immediately swept away.

Moreover, harmful dust particles had penetrated between the cover glass and the image plate in the cases where the black paper tapes were missing or were loose failing to withhold them sufficiently. In this case, it was imperative for cover glasses to be fully removed in order to ensure that the whole structure would be completely clean before reassembling and no dust particles would be trapped in-between. Removing the paper tapes resulted in adhesive residues all around the edges of both glass components, cover and image (fig. 7a, fig. 7b). Additionally tape residues were observed in cases where tapes were missing due to lack of adhesion. These residues were removed with the usage of solvents applied with cotton swabs.

The stabilization of the delaminating image layer was observed in Autochromes that had no cover glasses. This treatment was kept at a non invasive level since the fragile areas were limited and mostly around the edges. It was decided that it would be of benefit to the Autochromes not to apply any kind of adhesive for reattaching the emulsion on its glass support. Instead, the detached image layer was supported by placing a cover glass against it and binding them together.

Another challenging conservation treatment performed in 19 glass plates was the removal of the harmful commercial tapes that had been used extensively. First, the adhesive vehicle was removed mechanically with the aid of a spatula or a scalpel. Then the adhesive itself was chemically removed by using the appropriate solvents. Special care was taken so as not to allow any chemicals to penetrate through the cracks and come in contact with the light-sensitive emulsion layer that could result in creating stains. When the adhesive was completely removed, the next step was the replacement of the missing or broken cover glasses with new ones of the same size as the original. This treatment was performed in 13 items. Additionally two important factors were considered in the choice of the new cover glasses: their thickness – to be the same as the original – and their composition – to be chemically stable (fig. 8a, fig. 8b).

Fig. 8a and b : broken Autochrome plate before and after treatment (move the cursor to display the restored plate)

Finally, in 52 cases the missing or detached black paper binding tapes were replaced with new archival ones. The chosen archival tape was Filmoplast P90 which is made of wood-free, acid free tissue and has certified anti-aging properties from the Foundation for Paper Technology. It is a long fibre, tear-resistant, white paper tape. Therefore, it had to be coloured black to match the original one. This was achieved with the usage of permanent pens with archival quality inks that wouldn’t leak or stain and would remain unaffected by water. The latter was important in order to ensure that the black colouring would remain stable in case of high humidity levels and from the moisture of human handling (fig. 9a, fig. 9b).

Fig. 9a and b : broken stereoscopic view during and after treatment (move the cursor to display the restored plate)

Housing

Upon reception of the archive, different sized glass plate formats were stacked horizontally on top of each other. This storage method was inappropriate, as it placed significant pressure on the plates, particularly those at the bottom of the stacks and also compromised safe handling. The most efficient storage system was vertical housing, aiding to easy object retrieval while promoting safe handling of the collection.

When conservation treatment for each item was completed, it was placed in an archival four-flap envelope of the same size (fig. 10). The paper quality of these envelopes had to meet the criteria for conservation standards – being free from harmful components and any off gassing chemicals that could cause oxidation of the image silver or staining and deterioration of the gelatin. The selected envelopes had passed the Photographic Activity Test (PAT) and were certified for direct contact with photographic materials providing them a safe micro-environment. These envelopes had a smooth surface for avoiding any further abrasion or lifting of the image layer. The items were numbered on the outer side of their four-flap envelope with pencil in accordance with the index numbering given from the curator of the archive.

Next step was to place the glass plates vertically one after the other in archival boxes. Safe handling practices were taken into account when considering the number of storage boxes to be purchased. Having too many plates in each box would result in very heavy boxes, putting the objects at risk when accessed. Therefore, they were kept light ensuring a safer handling of the archive, especially when retrieving boxes from upper shelves. These boxes fulfill quality manufacturing criteria for ageing-resistant paper materials and have also successfully passed the PAT, offering optimal protection against harmful environmental influences.

Special care was given in the case of the 7 cracked and broken glass plate negatives, which were housed separately from the intact ones. Two four layered sink mat cases (fig. 11) were constructed from archival museum quality boards in order to match the thickness of the glass plates. The glass cover was kept for the cracked and broken glass plates in order to retain their original structure. Therefore, the broken parts were put together and rebounded with a cover glass (either existing or new) and new black paper tapes. It was very important to avoid any contact of the cracked and broken parts with the new tapes. This was achieved by interleaving a piece of Mylar sheet of the same size between them (fig. 12).

Conclusion

The study of the materiality of the 315 glass plates from Joseph Chamonard’s archive gave us the opportunity to evaluate his intentions and method of work from another perspective. His conscious choice to record his findings in colour in such an early stage in the evolution of colour photography; the acknowledgment of the importance of three-dimensional images in order to reveal the details and all the information of an artifact; his willingness and determination to continue using glass plates while having the opportunity to use the light-weight flexible film and to overcome the strain of carrying his heavy equipment in the rough archaeological sites with the risk of breakage. These are all focal points for contemporary archaeologists and photographers on Chamonard’s wide interdisciplinary perception. The undertaken conservation and rehousing treatments have contributed decisively to the longevity and preservation of Chamonard’s work for the future. Moreover, these items can now be safely digitized, improving accessibility to researchers as the archive can be studied further enabling public awareness of Chamonard’s work.

Dessy GRIVA

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