The conservation and restoration of paintings is carried out by professional painting conservators. Paintings cover a wide range of various mediums, materials, and their supports (i.e. the painted surface made from fabric, paper, wood panel, fabricated board, or other). Painting types include fine art to decorative and functional objects spanning from acrylics, frescoes, and oil paint on various surfaces, egg tempera on panels and canvas, lacquer painting, water color and more. Knowing the materials of any given painting and its support allows for the proper restoration and conservation practices. All components of a painting will react to its environment differently, and impact the artwork as a whole. These material components along with collections care (also known as preventive conservation) will determine the longevity of a painting. The first steps to conservation and restoration is preventive conservation followed by active restoration with the artist's intent in mind.
Basic care Typical, traditional oil, acrylic, and many other types of paintings are made up of various different types of materials, from their paint layers to the materials that make up their supports. Each of these materials requires specific care in handling, displaying, storage, added protective measures, and general environmental conditions. Providing the proper care to each of these materials ensures that the overall condition of the painting is protected.
Backing boards Using good protective measures such as attaching a rigid backing to a painting on canvas provides several protections. It reduces the effects of rapid changes in relative humidity around the painting, provides some protection from pressure or direct contact against the canvas back, and protects from vibrations caused by handling or moving. Backing boards also serve to protect from dust and dirt, cracks and deformations from handling, and insect activity. Some of the most commonly used types of backing boards include foam core, heritage board, matboard, cardboard/millboard, coroplast, corrugated plastic sheets, acrylic sheeting, mylar, and fabric.
Framing The frames around paintings are not just for aesthetic appearances. Frames are also used to protect the more sensitive parts of a painting when handled by hand, and they reduce the potential for damage if the painting is dropped. There are also specialists that work on the conservation and restoration of painting frames.
Handling and moving The movement of objects places an object at a much greater risk of damage than when it is on display or in storage. Certain techniques and equipment are used any time an art work needs to be transported. These techniques and equipment include using padding lifts and dollies, moving small, fragile objects on carts instead of carrying by hand; lifting objects from underneath by their sturdiest part; and taking extra time and care when on ladders or stairs.Swain, L. (2010). Museum registration methods 5th edition. Washington, DC: The AAM Press, pg. 298. In many cases gloves are worn to protect the art work from any dirt or oil that may be on a conservator or object handlers hands. When handling canvas paintings specifically, never presume that the frame is stable and firmly attached. Do not lift or carry a painting by its stretcher bar, or insert your fingers between the stretcher bar and the canvasNeilson, D. (2010). Museum registration methods 5th edition. Washington, DC: The AAM Press, pg. 212.
Display and storage It is estimated that a lack of proper routine maintenance and care is responsible for 95 percent of conservation treatments; the remaining 5 percent results from mishandling objectsFisher, G. (2010). Museum registration methods 5th edition. Washington, DC: The AAM Press, pg. 286. When developing display and storage methods for works of art, issues regarding relative humidity, temperature, light, pollutants, and pests need to be considered. Location and the types of storage units must be considered as well. Storage areas should be located in areas away from pipes and heating systems, as well as out of areas that are likely to flood and collect dust and dirt. Storage units should be sturdy, adjustable for collections growth so all collections sizes are safely stored, made of materials that will not cause any damage to the paintings (i.e. metal racks), and be free of any hardware or supports that stick out.
Causes of deterioration Moisture, heat, light, pollutants, and pests can slowly or suddenly cause damage to a painting. A non-comprehensive list of agents of deterioration impact all of the components that make up a painting in various ways includes: Accidents Acts of vandalism / defacing / iconoclasty - People have damaged or destroyed artwork during war and peacetime. For example, during the Iraqi invasion of Kuwait, Saddam Hussein damaged buildings and artwork. Another example is the destruction of paintings by political activists. Inherent chemical degradations / Materials obsolescence and incompatibility Mold Relative humidity and temperature - Too low or too high relative humidity (RH) as well as rapid changes in relative humidity can be damaging to paintings. According to the Canadian Conservation Institute, there are four types of incorrect relative humidity: dampness over 75% RH, RH above or below a critical value for that object, RH above 0%, and RH fluctuations. "Generally accepted temperature and relative humidity standards for most museum objects and artifacts are 65°–70°F (18°–21°C) at 47%–55% RH." The best method of controlling the environment is by using a centralized climate control or HVAC system where incoming air is washed, cleaned, heated, or cooled, adjusted to specific conditions, and then injected into the storage space. An appropriate alternative is a localized climate control system where air conditioners cool the air and absorb some of its moisture while filtering out gross particles. They do not condition the air, nor do they filter air pollutants. Light - Both visible and ultraviolet light can cause damage to paintings. In particular, organic materials such as paper, fabric, wood, leather, and colored surfaces. "Fugitive dyes and colorants used in paints will eventually discolor under exposure to ultraviolet light. The fading of pigments and dyes in paintings will affect the color balance of the image." Damage from natural and artificial light exposure can be mitigated by displaying paintings out of direct sunlight, use of blinds, shades, curtains, or shudders, filters on nearby windows, installing dimmers and appropriate wattage light bulbs, and displaying paintings a safe distance from a light source to limit heat exposureLandrey, G., & Hoag, R. (2009). The Winterthur Guide to Caring for Your Collection. University Press of New England. Airborne pollutants - originate from atmospheric sources (ozone, hydrogen sulfide, sulfur dioxide, soot, salts), or emissive products, objects, and people (sulfur-based gases, organic acids, lint, and dander). Their effects can include acidification of papers, corrosion of metals, discoloration of colorants, and efflorescence of calcium-based objects. Pollutants transferred by contact - plasticizer from PVC, sulfur compounds from natural rubber, staining materials from wood, viscous compounds from old polyurethane foams, fatty acids from people or from greasy objects, and impregnation of residue of cleaning agents. The effects of these pollutants can include discoloration or corrosion of a paintings surface. Intrinsic pollutants - composite objects that have compounds that are harmful to other parts of an object. The effects of these pollutants includes deterioration of the object, acidification, discoloration or staining on an object, speed up degradation processes caused by oxygen, water vapor, or other pollutants. Pests such as rodents and insects - they have the potential to cause considerable damage to works of art. Preventive measures that may be taken to protect paintings from pests include upgrading building structures to obstruct pest entry, installing better cabinetry with good seals, better control of temperature and humidity in collections and storage areas, keeping food and other organic materials from collection areas, and treatment of outbreaks. Materials that are commonly damaged by pests include: natural fibers, wood, paper, starch adhesives, and egg tempera.
Recommended environmental conditions and potential damage Materials Recommended Relative Humidity Levels Potential Damage Recommended Light Levels Potential Damage Recommended Temperature Levels Potential Damage AcrylicGovernment of Canada; Canadian Heritage; Canadian Conservation Institute. (18 April 2016). Environmental and Display Guidelines for Paintings. Retrieved 8 April 2017, from http://canada.pch.gc.ca/eng/1439925170465 40–60% Low humidity causes warping and splits, and high humidity causes wrapping, sagging, and buckling max 50 Lux Permanent changes in pigment, dry paint out, and create cracks and paint flakes 65 °F–70 °F High temperatures soften a painting and allow dirt to stick to surface. Low temperatures cause paintings to become brittle. Canvas 50 ± 10% Collects dust easily max 200 lux 68 °F ± 2° Collects dust easily Ceramics 50% ± 5% May result in weeping and crizzling or max 300 Some types of glass may turn purple from solarization 68 °F ± 3° Causes expansion and contraction possibly resulting in breaking or crack. Cloth/Textiles 40–50% Mold and mildew, increased insect activity max 50 lux faded fabric dyes, fabric becomes brittle 55 °F–68 °F Thermal degradation Enamel 50 ± 10% High temperature sensitive max 300 lux Too much light creates heat and causes damage 68 °F ± 2° High temperature sensitive Encaustic 50 ± 5% Thermoplastic or embrittlement max 200 lux create too much or too little heat and cause distortion or embrittlement 68 °F ± 2° Thermoplastic or embrittlement Glass 50% ± 5% or 40–45% for weeping glass Cleavage and flaking of paint max 300 lux Not generally sensitive to light, but paint layer may be impacted 68 °F ± 3° Chemical and physical deterioration can be worsened by fluctuations in temperature Ivory 35–55% High humidity causes warping, splitting, buckling, or dimples. Low humidity causes the ivory to become brittle max 50 lux Fade in pigment colors 65 °F–70 °F Warping and cracking, paint flake Lacquer Paintings 55–60%Degradation by oxygen, shrinkage, and internal stress Blanching, whitening, and formation of salts max 150 lux Fading and discoloration 68 °F Changes in color on the lacquer surface, loss flexibility and toughness Metal 40–50% The lower the RH the less chance of corrosion, but paint may become brittle max 300 lux Increased heat from light creates paint soften 68 °F ± 2° High temperature softens paint. low temperature causes brittle paint. Oil Paint 40–45% or 45–45% Expansion and contraction of painting, wood and fabric absorb moisture or shrink, paint cracks and flakes, or sags max 200 lux Fading or darkening of painting 65 °F–70 °F or 70 °F–75 °F Expansion and contraction of painting Pastels 50 ± 10% max 50 lux Example 68 °F ± 2° Paper 40–50% Discoloration, planar distortion, cockling, microbiological attacks, increased presence of insects max 50 lux Discoloration, faded pigments 68 °F–70 °F Cellulose breakdown, decreases life expectancy. Scroll/Screen Paintings 50–60% Mold, physical distortion, and embrittlement max 50 lux fade in colors, physical deterioration of silk and other organic materials 65–70 °F Physical distortion and embrittlement Watercolors & Gouache 50 ± 5% Binder in paint can become friable max 50 lux Color fade and discoloration 68 °F ± 2° Deterioration of binder Wood 45–50% Warping, cracking, shrinkage, swelling max 200 lux High light levels can increase temperature causing warping, cracking, and shrinkage 20 °F ± 2° Warping, cracking, shrinkage, swelling