Compared to conventional photographic processes, photogravures are vastly more stable. Among the medium’s other exceptional attributes, no doubt permanence was a factor influencing master photographers to invest the time, effort and expense necessary produce high quality gravures. By the early 20^th century, when the photogravure rose to such prominence as a reproduction medium for photographs, the basic components that form the print, oil-based ink and paper, were well understood from the standpoint of stability. Photographers especially welcomed the promise of durability as they were with accustomed to grappling with permanence issues associated with photographic prints.

Though extremely durable, photogravures are not impervious to damage and gradual deterioration. Every photogravure, indeed every intaglio print and most other works on paper, remain especially susceptible to deterioration mechanisms broadly classified under the headings: chemical, physical and biological.

Chemical

For work of art or cultural artifact of any sort, virtually any chemical interaction with the environment is a potential form of deterioration. For photogravures, the most susceptible component is the paper base. The chemical degradation of paper is most often catalyzed by long-term exposure to elevated relative humidity and light.  Moisture from the air interacts with cellulose to break chemical bonds along the polymer chain and to produce acidic deterioration products that then serve to catalyze additional deterioration. With time, these changes are usually manifested in the gradual overall darkening of the paper base and increasing brittleness.  Exposure to light will have a similar effect caused by the photo oxidation of cellulose and the accumulation of chemical deterioration products. Temperature is a significant variable governing the rate of any chemical reaction, including those catalyzed by moisture and light.  Over the years, museums and other cultural institutions have developed guidelines to take these factors into account. A common recommendation for museum storage of works on paper is a range of 30% to 50% relative humidity (RH) and temperature not to exceed 68^oF (20^oC). As damage caused by light is mainly due to duration of exposure and intensity, most institutions will limit light levels to 5-9 foot-candles (54 -97 lux) and rotate exhibitions of works on paper on and off display after several months.

Housing materials, such as mats, interleaving papers, frame backings and boxes can greatly assist or undermine the preservation of photogravures. Paper-based enclosures should be lignin-free (lignin is an acidic resin found in wood) and composed of cotton fiber (“rag”) or highly purified wood pulp. The addition of an alkaline buffer to paper enclosures is recommended to help counteract acid-based deterioration. The importance of good quality interleaving paper for intaglio prints in storage is essential as the linseed oil ink medium used for these prints can be fairly acidic and cause localized staining among stacked prints. Plastic sleeves, used in addition to or as an alternative to paper enclosures, should be composed of chemically inert materials such as polyester, polypropylene or polyethylene.  Plastic sleeves of unknown composition should be discarded.  Whenever possible, handling should be limited to the print enclosure as finger oils can cause staining over time and embed surface dirt. If prints do require direct handling, the use of white cotton gloves is recommended.  On display, frames should incorporate a glazing material that filters for ultraviolet.  These higher energy wavelengths (relative to visible light) catalyze proportionally greater degrees of deterioration.  Good quality housing materials, including frames, museum cases and other storage boxes also can significantly help reduce the impact of fluctuations in relatively humidly.  This attribute can be a significant benefit to the private collector that is unequipped to maintain a constant level of moderate relative humidity.

Physical

Physical deterioration of prints typically refers to problems such as tears, folds and distortions.  In most cases, tears and folds are the result of careless handling.  In general, prints without mats should be handled using a rigid secondary support, such as a piece of good quality mat board. Distortions, either local wrinkles or overall warping and buckling, can be the result of improper storage materials but also due to fluctuations in relative humidity.  Paper expands in contracts in response to moisture content in the air. Adhesion of a photogravure to a secondary support can restrict these dimensional changes and cause severe local distortions.  These distortions are very common in Camera Work and other photogravures where adhesive is placed in a small area behind each of the four corners of the print.

Biological

Biological deterioration is the result of attack by flora and fauna. Paper can be a very inviting material for all manner of insect and rodents. Preventing such infestations usually centers on creating as inhospitable of an environment as possible by keeping storage areas clean and free of moisture and food. Possibly of greater concern for the collector, various species fungi can exploit trace inorganic components in paper to sustain their metabolism.  Such interactions can eventually cause local red/brown stains to develop on paper commonly referred to as “foxing.”  Again, the key to prevention is maintaining cool, dry, conditions as fungal growth accelerates as temperature increases and at humidity levels consistently above 60%.

Treatments

The deterioration mechanisms mentioned above have been studied in depth by paper conservators and conservation scientists resulting in a great deal of literature from which additional preservation guidelines and best practices can be distilled. From this work, numerous paper conservation treatments useful for stabilizing the condition of prints have emerged. For staining caused by chemical and biological deterioration, washing in deionized water may be extremely useful to stabilize the condition of the print and reduce stains.  For greater stain reduction, bleaching treatments can be effective; though these treatments need to be applied judiciously as there is a risk of causing additional deterioration. At times, an alkaline reserve, such as calcium carbonate, can be applied to the paper to slow the rate of acid-based deterioration.  Physical deterioration like tears can be stabilized through the application of fine strips of Japanese paper to the reverse of prints, generally using adhesives like wheat starch paste and / or methylcellulose. Distortions can be reduced by imparting moisture to the paper then gradually drying between smooth blotters under weights.  The intrinsically good quality materials used to make most photogravures is a tremendous advantage should conservation treatment be necessary.  For most paper conservators the techniques and material used to treatment photogravures are relatively routine, conventional and time-tested, especially as compared with other media like photographs. Conservation treatment, however, should never be approached casually and should only be carried out by a professional with training and experience.  Over time most serious collectors will assemble a “team” of experts upon which they can rely for guidance. A conservator should be part of this team. Working with a conservator can help collectors build a more sophisticated level of discernment identifying which photogravure condition problems can be successfully treated and which can not. The American Institute for the Conservation of Historic and Artistic Works (AIC) offers a publicly accessible database listing conservators sorted by their geographical location and area of expertise as well as more in depth information on photographic print conservation.

Special thanks to Paul for contributing his expertise to this project.