Preventive conservation and transport of artworks
Reasercher of Archaeology museum
Basics of preventive conservation
Although treatment of an object may sometimes be necessary, treatment alone is not sufficient to preserve collections for future. Objects inevitably deteriorate, but our objective as preservers of material culture is to slow the rate of deterioration as far as possible. Preventive conservation efforts aim to reduce damage and deterioration to collections by improving their environment. Measures include areas such as: Controlling temperature, relative humidity and pollutants; Archival housing; Loan documentation and packing for transport; Integrated Pest Management; Cleaning and housekeeping; Emergency preparedness and response; Handling procedures; Hazardous materials.
Relative Humidity, Temperature and Pollutants
Thermodynamics of humid air
All materials respond to their immediate environment. Very high relative humidity is conducive to mold growth. Fluctuating relative humidity causes organic materials like wood, ivory, and paper to cycles of expansion and contraction leading to cracks, broken paint, and warping. Particulate pollutants like dust, sand grains and soot are carried into the museum from urban and agricultural environments. Sharp grains like sand lead to abrasion of object surfaces. Soot is grimy and acidic leading to discoloration, embrittlement of organic materials and corrosion of metals. Relative humidity is a relationship between the volume of air and the amount of water vapor it holds at a given temperature. Relative humidity is important because water plays a role in various chemical and physical forms of deterioration. There are many sources for excess water in a museum: exterior humidity levels, rain, nearby bodies of water, wet ground, broken gutters, leaking pipes, moisture in walls, human respiration and perspiration, wet mopping, flooding, and cycles of condensation and evaporation. All organic materials and some inorganic materials absorb and give off water depending on the relative humidity of the surrounding air. Metal objects will corrode faster at higher relative humidity. Pests are more active at higher relative humidity. We use relative humidity to describe how saturated the air is with water vapor. “50% RH” means that the air being measured has 50% of the total amount of water vapor it could hold at a specific temperature. It is important to understand that the temperature of the air determines how much moisture the air can hold.
Preventing damage to objects is more cost-effective than allowing the damage to happen and then treating it.
Pollution impact on cultural heritage: impact assessment and strategies for preventive conservation
Acidic gaseous pollutants from urban traffic have caused this gold alloy figurine from Peru (FMNH 2414) to tarnish everywhere except under the varnish associated with the catalog number on its chest.
Some materials may be inherently unstable and require a specific environment to reduce further degradation. For example, soda-lime-silica glass that was not made with the correct proportion of silica, soda flux and lime stabilizer will degrade with high and fluctuating relative humidity (glass hydration disease). This glass will continue to degrade unless held at a very constant relative humidity of 40-42%.
The white crystals on these beads from are flux and stabilizer ions from the glass that leached out with fluctuating humidity and then combined with carbon dioxide in the air to form the white carbonate minerals.
Light is another agent of deterioration that can cause damage to museum objects. Light causes fading, darkening, yellowing, embrittlement, stiffening, and a host of other chemical and physical changes. This section gives an overview of the nature of light. It will help you understand and interpret monitoring data and the standards given for light levels in museum storage and exhibits. Be aware of the types of objects that are particularly sensitive to light damage including: book covers, inks, feathers, furs, leather and skins, paper, photographs, textiles, watercolors, and wooden furniture. All types of lighting in museums (daylight, fluorescent lamps, incandescent (tungsten), and tungsten-halogen lamps) emit varying degrees of UV radiation. This radiation (which has the most energy) is the most damaging to museum objects. Equipment, materials, and techniques now exist to block all UV. No UV should be allowed in museum exhibit and storage spaces. The strength of visible light is referred to as the illumination level or illuminance. You measure illuminance in lux, the amount of light flowing out from a source that reaches and falls on one square meter. We measure illuminance in museums because we are concerned with the light energy that falls on our objects, not how much light energy comes from the source. When you measure light levels, hold your meter at the surface of the object to catch the light that is reaching that surface. Illuminance was previously measured in footcandles. You may find older equipment or references that list footcandle levels. Ten footcandles equal about 1 lux. When considering light levels in your museum you should keep in mind the “reciprocity law.” The reciprocity law states, “Low light levels for extended periods cause as much damage as high light levels for brief periods.”
Monitoring and Controlling Light
To be sure that light levels are at required levels and to be sure that any UV filtering material is still effective, you should measure light levels at least once a year. If you change lighting fixtures, take new measurements to be sure the changes are within recommended levels. If the source of light is daylight (for example, in a historic house museum) you should measure light in the morning and afternoon throughout the seasons.
For long term preservation, it is critical that object housing provides physical support to the object and that the housing materials are archival (chemically stable materials that will not cause harm to the object). Conservation staff study manufacturer’s data and conduct artificial aging and chemical tests of materials to select materials for storage housing and display mounts that are archival. The object structure and condition determines the support needed to prevent distortion and breakage over time.
Loan Documentation and Packing for Transport
All objects going on loan to other institutions are carefully examined to make sure they can safely travel and are packed to reduce the vibration and shock inherent in vehicular and air transport.
The problem of how to transport works of art and other cultural artefacts is one which has preoccupied for centuries artists, art-collectors, curators and many others interested in art. It is not by chance that, above all since the Renaissance of the 15th and 16th Centuries, painting has been executed mostly on flexible materials such as textiles. A rolled-up canvas, after all, is much easier to transport than a wooden panel, especially if the painting executed on it is of a larger size. Ideally, a transport crate for an artwork should guarantee, in its interior, environmental conditions identical to those in a museum, even when external influences are at their harshest. The relevant negative external influences likely to be met with in a museum are summed up in a list entitled “Ten Agents of Deterioration”. The transport crate itself should offer especial protection against climatic fluctuations, sudden impacts and vibrations. The other “agents of deterioration” – such as fire, theft, flood etc. – should be excluded by means of securing procedures carried out prior or parallel to the crating.
How effective the crate is against climatic fluctuations, impacts and vibrations can be tested in environment labs. Product standards and guidelines prescribe the stress tolerances in these regards. Super-sensitive sensors are used to monitor the crates’ reactions to fluctuations in environmental conditions.
IPM (Integrated Pest Management)
Protecting the collections from damaging pests is a museum-wide endeavor. The Museum Pest Committee, working with contract pest specialists and entomologists, includes members from each division of the museum, including Facilities, Housekeeping, Collections, Exhibits, Special Events, Administration and Institutional Advancement. The Committee tracks pest activity in the museum and immediate grounds, advises on and coordinates pest mitigation and response activities. Given that many collections within the Department of Anthropology are highly attractive to insect, rodent and mold pests, Anthropology staff are highly sensitized to the danger of a pest infestation.
Cleaning and Housekeeping
Dust and debris in collection storage and workrooms provide attractive environments for damaging pests. Dust falling on objects is often difficult to remove without disrupting the fine structure of materials like feathers and matte paint. Access to storage is limited to reduce the build-up and movement of dust and dirt. Workrooms are regularly cleaned by housekeeping staff. Anthropology staff conduct an annual in-depth cleaning of all storerooms to remove any clutter that may have accumulated and reduce the dust load in storage.
Emergency/Disaster Mitigation and Response
Disaster Planning includes identifying potential risks to the collections, mitigating those risks through improvements to the building, the object storage and exhibit furniture, and procedures. Disasters may be caused by natural events like flooding, tornados, earthquakes, and by man-made situations like leaking pipes, breakage of vitrines and fire. The Anthropology Department developed and maintains a policy and procedures for responding to disasters. We work with local agencies like the Chicago Emergency Response Office, the fire, Police, and other Chicago cultural institutions, to identify resources available.
When accidents do occur, museum staff respond immediately to reduce damage to collections.
Objects can suffer breakage and staining through inappropriate handling. All department staff, researchers, interns and volunteers are given training in lifting, supporting and transporting objects. Gloves are worn to prevent the deposition of hand oils, perspiration and soil. Padded carts with pneumatic wheels are used to move objects. Safe ways to lift different object types are reviewed.
Hazardous materials pose a risk for staff working with collections. Some hazards may be inherent to the objects themselves, for example pigments made of arsenic or mercury minerals. In other cases, toxins may have been applied to an object in early efforts to reduce insect damage. Objects are tested for toxins [photos sampling, testing] and housed and labeled if positive [photo labeled housing]. Procedures have been developed with the Field Museum health and safety officer and public health advisors to protect staff and researchers who handle collections. Gloves, lab coats and sometimes masks are worn to protect staff.