Osmond Watson – City Life (1968, Collection: NGJ). This oil painting on canvas suffered from significant flaking and paint loss
In the early years of its operations, the NGJ has employed conservators, Trevor Burrowes and Stanley Barnes, and more recently the NGJ has benefited from various short-term conservation projects. We are now developing a long-term, in-house conservation programme, as part of our dcollections management. Here is the first section of a two-part article on tropical conservation by Joelle Salkey, a Jamaican art conservator who has recently joined our staff.
When defined in the scope of art and heritage conservation, the tropical climate presents a major source of problems for the display and storage of material collections. While tourists flock to the warm balmy climate, conservators scramble to find cost effective climate controls to maintain lower temperatures and reduced humidities. This is due to the fact that the unchecked tropical climate falls drastically outside of the conventional climate control specifications, of 21 degrees Celsius with 55% Relative Humidity (RH), established by twentieth century conservation professionals.
The obsession with identifying the ideal environment for artwork and museum objects assumes that the farther you stray from the ideal target the greater the damage posed to collections.[1] However tropical climates typically register temperatures averaging 24-27 degrees Celsius with a relative humidity of 65-70%. Following this, tropical temperatures are conducive to increasing the rate of decay in museum objects, with the rate of chemical and biological activity doubling for every increase in temperature of 10 degrees Celsius[2].
To make matters worse, tropical regions are disaster prone, suffering from more occurrences of hurricanes and earthquakes than other climate regions. Natural disasters are unpredictable and although they cannot be prevented, risk management offers a line of defence for a tropical collection. The concept of risk management is appearing ever more frequently in conservation literature[3], indicating that the old adage “prevention is better than cure” is very important in preserving the longevity of a collection.
Osmond Watson – City Life (1968, Collection: NGJ), afer its restoration at the Western Centre for Arts Conservation, Denver, Colorado, in 2010. This conservation project was funded by the US Ambassadors’ Fund.
A risk assessment – whether formal or informal, extensive or conducted on just a small section of a collection, is a useful tool used in museums and other cultural institutions to prioritize the execution of preventive conservation methods. The goal is to hopefully prevent damage or, at least, to limit the extent of the damage. By estimating and calculating risks, museums and conservators can create measures to counteract hazards and to the best of their ability protect objects of cultural heritage.
The creation of risk assessments leads to a better understanding of the museum objects and how they respond in their various environments. Relative humidity and temperature are two of the most dangerous risks to an object’s permanence. Hence through risk assessment in conservation the museum or cultural institution can better evaluate suitable ranges of temperature and humidity to store and display objects.
With regards to the museum environment, museums and collectors face the challenge of finding a balance between the ideal climate and financial feasibility. This challenge is easier to accomplish if the objects being stored or displayed are of a similar makeup. For example, if a wooden sculpture is placed (as it should be) in storage with similar wooden objects, it is easier to follow the recommended storage temperature of 12-18 degrees Celsius and a humidity of 50-60%[4]. However, complex or composite objects consisting of more than one material in their makeup, are a bit more difficult to correctly store at their ideal temperature. A broader range is given to composite objects, designating 16-18 degrees Celsius in temperature and a 40-55% humidity range.
A painting is considered a composite object, simply as it is composed of many different materials adhered together. Understanding the various components of a painting aids significantly in identifying the correct storage environment. In their composition, paintings traditionally consist of about three layer categories: the support layer, the preparation layer and the image layer. Each layer reacts differently to various temperatures and humidities. The support layer in traditional painting is identified as the wooden stretcher or panel along with the stretched canvas. The preparation layer includes the ground size that is put on to prepare the canvas to accept the artist’s design. The image layer consists of the paint layers and the varnish layers. The incorrect preparation of any layer can severely affect the longevity of the painting. Each layer is also individually vulnerable to different risks presented in the environment that houses the painting.
The devastating effect of humidity and temperature is more evident in heritage objects made from organic material. Plants and animals contain a high proportion of water. Naturally their products, such as paper, cotton, leather, fur etc. are hydroscopic- meaning they are affected by moisture[5]. These materials will give off moisture to and absorb moisture from the air until there is an equilibrium point- a point where no more moisture can be absorbed and no more can be released. If the air around where the object is stored is dry, the artwork will release moisture until it is brittle and shrinks, warps or cracks. If the air around the object is moist, the art object will absorb moisture until it is distorted, cockles and cracks.
In the case of traditional paintings, the most susceptible components to humidity are the wooden stretcher or panel board and the canvas. As these elements comprise the support layer of the work, the other layers will over time begin to exhibit stress due to excessive fluctuations. In uncontrolled dry environments, shrinkage and cracking develop in colour pigments as binders lose moisture, while in uncontrolled damp environments, natural fibres swell encouraging softening of adhesive bonds and flaking.
There is a great challenge to museums and collectors wanting to practice preventive conservation in tropical environments, as there can often be several agents of deterioration acting simultaneously.[6] To clarify, the warm climate encourages problems due to humidity; humidity in turn encourages physical, biological and chemical damage. Humidity-driven physical damage can manifest itself as flaking of paint pigment from the surface of a painting. In warm humid environments RH-responsive materials, such as the size, gesso or binders in which the pigments are mixed, lose strength resulting in eventual paint loss.
Biological damage can occur when the humidity (65% and above) provides a comfortable environment to encourage the growth of mold or pest reproduction and nesting. Naturally, all livings things absorb nutrients, reproduce and excrete – three actions that when observed in the context of priceless works of art make conservationists cringe.
In some ways the chemical damage is linked to the biological deterioration of artwork. Excretions can oftentimes interfere with the delicate chemical structure of the surface of a painting. Other forms of chemical damage include occurrences of air pollution, in which gaseous chemicals mix with water found in the atmosphere. The resulting mixture settles on the surface of paintings and causes acid damage. Environmental issues such as fossil fuel combustion and waste produced by industrial processes release air pollutants such as oxides of sulphur and nitrogen into the atmosphere.[7]
Dust often carries a mix of organic material and chemical particles which could over time affect the surface layer of paintings, introduce biological threats or encourage pests to feast on the organic material found within the paintings.
Joelle Salkey is a recent graduate of the St. Petersburg State University of Culture and Art, in St Petersburg, Russia, were she completed her masters degree in Museology and Protection of Objects of Culture and Natural Heritage. She is also a graduate of the Edna Manley College of the Visual and Performing Arts where she earned her BFA in Painting. Joelle has received training as a conservator for paintings and murals, and has worked on restoration projects throughout the island.
NOTES
[1] Michalski, S. The Ideal Climate, Risk Management, the ASHRAE Chapter, Proofed Fluctuations and Toward a Full Risk Analysis Model. Contribution to the Experts’ Roundtable on Sustainable Climate Management Strategies, held in April 2007, in Tenerife, Spain. The Getty Conservation Institute. P. 1
[2] Teygeler, R. Preservation of Archives in Tropical Climates. An annotated bibliography, Comma, Paris, 2001. P. 38
[3] Waller R. Conservation Risk Assessment: A Strategy for managing resources for preventive conservation. p.12
[4] Первак В. Э. Обеспечение сохранности этнографических коллекций в музей. Методическое пособие. Министерство культуры Российской Федерации Российский Этнографический Музей. Санкт-Петербург 2011. С. 15
[5] Museums Australia Victoria, Temperature and Humidity, http://www.mavic.asn.au/assets/Info_Sheet_4_Temperature_and_Humidity.pdf (April 2014)
[6] Teygeler R. Preservation of Archives in Tropical Climates. An Annotated Bibliography Paris/The Hague/Jakarta, International Council on Archives/National Archives of the Netherlands/National Archives of the Republic of Indonesia, 2001 http://cool.conservation-us.org/byauth/teygeler/tropical.pdf (October 2013) p. 10
[7] United States Environmental Protection Agency, Sulphur Dioxide http://www.epa.gov/oaqps001/sulfurdioxide/ (June 2015)
