PMG Surface Cleaning
In progress: Seeking additional comments and images to develop this section
Photographic Materials Conservation Catalog
Date: Initiated July 2014
Contributors: Amy Brost, Luisa Casella, Ronel Namde, Stephanie Watkins
The Photographic Materials Conservation Catalog is produced by the Photographic Materials Group of the American Institute for Conservation of Historic and Artistic Works as a convenience for the membership. The treatments, methods, or techniques described herein are provided for informational purposes. The reader assumes responsibility for any application results.
- 1 Purpose of Surface Cleaning Photographic Materials
- 2 Factors to Consider Before Surface Cleaning
- 3 Techniques
- 4 Guidelines and Recommendations
- 5 References
Purpose of Surface Cleaning Photographic Materials
Maximize the chemical and physical stability of the object while removing damaging or obscuring surface deposits while minimizing changes in the image, binder, and support from light exposure while removing surface debris. Surface cleaning is sometimes referred to as "dry cleaning" although some methods can involve water, and should not be confused with chemical "dry cleaning" of textiles.
Factors to Consider Before Surface Cleaning
Photographs often present surface dirt or accretions. The reduction or removal of these maybe desirable for aesthetic reasons or long-term preservation as these extraneous particles may contribute to further damage by abrasion by being hygroscopic or by contributing to the chemical degradation of the object.
Cleaning the surface of photographs is a delicate procedure. The risks involved are physical (abrasion) and chemical (harmful interaction of solvents with the image layer). Surface cleaning procedures may cause permanent change in sheen or texture, two of the most important visual characteristics of photographic materials.
It is fundamental to carefully identify the photographic process as well as any existing protective layers such as varnishes which will respond differently to treatment than the specific photographic process surface. Additionally, the presence of hand coloring or retouching should be thoroughly considered before beginning any cleaning procedure.
It is also most important to evaluate the condition of the photograph prior to cleaning. Note silver mirroring, processing problems, evidence of mold or prolonged exposure to high RH, cracking of the binder or coating, etc. All of these will affect the choice of cleaning method; severe structural damage to a binder layer may rule out surface cleaning treatment or mandate that treatment be carried out under magnification at all times.
It is equally fundamental to determine the nature of the dirt to be removed which will allow defining the appropriate course of treatment.
- Particulate matter will often be easily removed with air bulb or brush
- Soot, from fire damage, is greasy and has to be removed by the use of solvent, eraser or soot sponge
- Fingerprints are often composed of grease or dirt so the use of solvent may be required, although often not be successful.
- Accretions may often be removed by mechanical action alone (using a sharp edged tool).
Mechanical (Dry/Non-aqueous) Cleaning Methods
With mechanical cleaning it is fundamental that the tools or surface deposits do not abrade or damage the surface of the photograph by excessive pressure, sharp edges or composed of too hard a material, since these tools will be cleaning the surface (as opposed to a solvent).
A safe approach to surface cleaning, if the surface deposits are minimal (such as dust), it the use of an air bulb. Even so it is important to work methodically and make sure to blow the surface dirt from the center outwards or from one edge to the other, making sure that the dirt is not being moved and re-deposited on the object’s surface in another area.
It is not advised to use compressed air cans for cleaning as they often spray chemicals or aqueous droplets that may damage the surface of the object. The use of ionizing air wands is being investigated at The Met. These work by breaking the electrostatic bonds on the surface of objects, releasing dust or other particulates, as well as by blowing air. Small museum vacuum cleaners may be used for light surface dirt.
Soft brushes can be used for removing slightly persistent surface dirt. The brush must be of natural soft hair (e.g. goat) such as the Japanese Hake (brushes). Clean brushes after each use by washing with neutral soap and lukewarm water.
For more persistent surface dirt such as dark dust or debris, eraser crumbs may be used.
Erasers used by photograph conservators are sulfur-free vinyl erasers, more commonly Magic Rub and Staedtler-Mars white eraser. Tests done specifically to address interaction of erasers with photographic materialsdemonstrated that any eraser will leave some particulate and plasticizer residue on the surface.
Eraser may be acquired already grated (in which case it is important to be sure to buy conservation grade materials), or may be grated using a ginger grinder or an electrical food processor. Once grated, the crumbs are sprinkled over the surface to clean in small areas, and rubbed gently using the palm of your (nitrile gloved) hand applying slight pressure, or using a round brush or using the eraser block itself, depending on the level of pressure needed. As soon as the crumbs become soiled they should be brushed off with a soft wide brush (Hake brush), and new crumbs used to continue.
Block eraser may also be used.
It is important to insure that mechanical cleaning is not done excessively, that is, to a point where the surface of the object starts to be abraded or burnishing begins to occur. Highly glossy surfaces or processes without binder may not be cleaned with eraser – the first because the residues will alter its appearance, the second because residues will be embedded in the paper fibers as well as in direct contact with the image forming material and adversely react with it over time.
Chemical Solvent Cleaning
Using solvents to clean photographs surfaces requires accurate process identification. Many processes can look similar yet respond differently with similar treatment.
Spot testing is desirable prior to treatment. Unpredictable damaging effects may occur by solvent cleaning.
Considerations: To give an extreme example, if one were to wrongly identify a printing out process as a gelatin when in fact it was a collodion, the use of alcohol on the binder would dissolve it and the image would be removed, disfiguring the object irreversibly. Ethanol will swiftly dissolve Collodion. Collodion can be confused with silver gelatin prints.
Even if resistant to the solvent, a surface may be irreparably changed – such is the case of high-gloss ferrotyped surfaces which will change if in contact with water. Silver mirroring in photographs will be permanently disturbed by solvent cleaning, so best untouched if its overall removal is not the treatment goal.
Another issue with solvent cleaning is the risk of swelling the binder material, causing the dirt to penetrate it and be trapped, resulting both in a worst aesthetic appearance and in risk of further damage by future interactions of the binder material with the dirt.
Solvent cleaning is commonly done locally, using a cotton swab that is only slightly moist (never saturated with the solvent), and by rolling it gently on the surface applying very slight pressure. Cotton should be changed after each swipe, to insure that the surface dirt is not being dragged across and re-deposited in another area or abrading the surface. Commonly solvent cleaning is done under magnification to ensure observing any possible occurring damage immediately.
Poultices may also be used for surface cleaning, notably for accretion removal, and generally in a localized area. Poultices of methylcellulose or Klucel-G used in a thick gel-like concentration allow slow humidification of the accretion which will bind with the poultice material and be more easily removed.
Solvent cleaning may also be done overall which is most delicate and risky and should only be done in processes which behavior is known. This procedure requires full attention of the conservator; it also requires the possibility to interrupt and neutralize the process if necessary, as often objects will react unpredictably. Overall solvent cleaning can be done by immersion in the solvent (washing) which may be applicable in cases where a fast humidification is desirable. Overall solvent cleaning may also be done by applying a solvent-soaked hygroscopic material over the photograph and have the dirt be transferred onto that material by capillarity. This is more appropriate if a slow humidification is required.
Solvents may be used to remove persistent surface dirt or adhesives such as pressure sensitive tapes or rubber cement.
Examples of solvents used both for local and overall surface cleaning are:
- De-ionized water – alcohol such as ethanol may be added, to increase evaporation rate of the water
- A surfactant such as photo-flo may be added to the water (in very low concentration – 0.5% to 3%) to increase the solubilization action of water
- Ethanol - pure or diluted in de-ionized water. The fast evaporation of ethanol may be desired;when a mix of water and ethanol are used, one can have the properties of water as a solvent with a fasting evaporation rate.
- Water with adjusted pH, such as ammoniated water
- Chelators added to water, such as citric acid or ethylenediaminetetraacetic acid (EDTA)
- A bath of toluene or acetone may be used for removing dry-mounted backings.
Ready to use commercial products should be avoided as their composition may be not fully disclosed.
There are cases where surface cleaning is particularly problematic.
A number of contemporary mounting methods pose great challenges to the conservator. Such is the example of face-mounted photographs where the photographic print has been surface-mounted onto a sheet of plastic glazing. The glazing then becomes the surface of the photograph but aesthetic reasons make it so that the object should be exhibited with no further protection,risking abrasion due to scratches by visitors and by the need of regular dusting.
Research at The Metropolitan Museum of Art allowed choosing a specific brand of microfiber cloth to dry clean these surfaces (Modern Magic® Blue Suede Cloth from Modern Plastics).
Laminating is another popular mounting method which consists of adhering a plastic layer to the surface of the photograph. These are commonly cleaned with air bulb only as the effect of direct use of cloths or brushes on these surfaces has not been researched.
Inherent silver particles migrating to the surface of a photographic print or negative can be disfiguring. Discussion on appropriateness of removal and techniques used can be found in the Silver Mirroring section.
Guidelines and Recommendations
It is advisable to perform spot testing prior to any surface cleaning, particularly when using solvents. Spot testing should be done in more than one area (for example high density and low density) as results may vary, and under magnification.
Whenever possible surface cleaning should be done under magnification or by regularly observing under magnification to ensure no damage is occurring. It is advisable to create mock ups to become familiar with working techniques as well as spot test prior to surface cleaning.
With some objects surface cleaning is a routine procedure, such as the case of face-mounted photographs. These cases represent an increased challenge as to which method to use, as incremental damage may be caused by cleaning procedure over time.
The back of a print or the secondary support it is mounted onto may be surface cleaned by a different technique than that of the photographic surface.
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