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The conservation and restoration of paintings, typically undertaken by a paintings conservator, employs basic collections care, with recommended conditions to prevent future damage, and restorative treatment methods to art works that already exhibit damage. As paintings widely vary from medium and support, their preventative conservation methods, and conservation and restorative treatments will vary as well. These varying mediums and supports combined makes preventative conservation and restoration complex. Each of these components of a painting can impact the artwork as a whole. [1]

Basic care

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Typical, traditional oil, or acrylic paintings are made up of various different types of materials. Each of these materials requires specific care in handling, displaying, storage, and general environmental conditions, that impact the overall condition of a painting.[2]

Backing boards

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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. [2] 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. [3]

Framing

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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 reduce the potential for damage if dropped. [2] There are also specialists that work on the conservation and restoration of painting frames.

Handling and moving

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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. [4] 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 canvas [5]

Display and storage

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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 objects [6] When developing display and storage methods for works of art, issues regarding relative humidity and temperature, light, pollutants, and pests need to be considered.

Causes of Deterioration

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Moisture, heat, light, pollutants, and pests can slowly or suddenly cause damage to a painting. These agents of deterioration impact all of the components that make up a painting in various ways.

Relative humidity and temperature

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Low or high relative humidity (RH) as well as rapid changes in relative humidity can be be damaging to paintings. According to the Canadian Conservation Institute, there are four types of incorrect relative humidity. These four types include: Damp, over 75% RH, RH above or below a critical value for that object, RH above 0%, and RH fluctuations. [7] "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 conditions 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.[8]

Light

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Both visible and ultraviolet light are responsible for causing 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." Cite error: There are <ref> tags on this page without content in them (see the help page). 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 exposure [9]

Pollutants

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Pollutants can be described as gasses, aerosols, liquids, or solids that have a chemical reaction with any part of a painting. There are three types of pollutants. Airborne pollutants, pollutants transferred by contact, and intrinsic pollutants.

Airborne pollutants which 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 include 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 are 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. [10]

Pests

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Pests such as rodents and insects have the potential to cause considerable damage to works of art. Preventative 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. [11]

Mediums and supports

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Painting mediums

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Acrylic paint
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There are two types of Acrylic paints used in acrylic paintings. There is solvent-based and water-based. Solvent-based acrylic paints are soluble in mineral spirits, and water-based acrylic paints are water-soluble. Acrylic paint differs from oil paint in both its quick drying time, and how the paint dries. Acrylic paint dries in as little as thirty minutes, and dries by the evaporation of solvent of water.

Blacklight or fluorescent/luminous paint
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Black Light or Luminous Paint is typically made up of fluorescent dyes mixed into paint. These dyes are not a typical dye, but rather a pigment that is suspended in a carrier or resin. This pigment is what gives off a glow when exposed to ultraviolet light. This glow or light is created by the energy that is released from the pigment. While the fluorescent paint layers reflect light, they lose their color intensity over time[12]

Egg rempera
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Egg Tempera is made up of egg yolk water, and pigment. These ingredients are mixed together to create a thick paste that dries quickly, but can take six to twelve months before it completely cures. Egg Tempera's fast drying property makes it difficult to correct or revise. [13] Egg Tempera and can develop cracks over time that are visible to the naked eye, and flaking caused by air bubbles. Tempera paintings are thought to be more resistant to materials typically used during cleanings. However, they are susceptible to abrasions from routine dusting, washings, and removal of old varnish layers.[14]

Enamel paint
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Enamel or nitro-cellulose based paints were originally designed for commercial use, but have also been used in artist's paintings such as Jackson Pollock and Pablo Picasso. Enamel paints are oil, latex, alkyd, and water based. This paint dries rapidly and has a glossy finish once dry. [15]

Encaustic
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Encaustic is a method of painting that involves dry pigments mixed with hot beeswax, then applied to the surface of a support such as wood or canvas. A completed painting is then finished by taking a source of heat to reheat the surface and fuse it together. Encaustic paintings do not require a varnish, are resistent to moisture, and do not yellow.[14]

Fresco
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Fresco paintings are a painting technique used on walls where pigments are mixed in water and then applied to wet lime plaster. As the wall dries, the plaster hardens, a transparent layer is formed, and the pigment becomes a part of the wall. Fresco colors needed to withstand the alkaline action of the line. Typical colors ranged from vine and ivory black to yellow ochre, umber, and cinnabar. Fresco paintings don't require a protective finish or varnish, but are especially susceptible to damage from damp conditions. Such damage could include paint layers flaking or detaching from the wall, orCite error: There are <ref> tags on this page without content in them (see the help page). a biological attack such as mold.[14]

Scroll and screen paintings
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Scroll Paintings,Hanging and Hand, and screen paintings are made of ink, color, pigment, silk and paper. Scroll paintings often are multiple layers of paper and silk attached to wooden bars called a stave and dowel. Screens are often single panels that are joined together by paper hinges that fold into each other like an accordion. Scrolls and Screens are vulnerable to damage from fluctuations in temperature and humidity. Exposure to light for extended periods of time can cause silk and pigments to fade, and paper to darken. Glazes and films that filter ultraviolet light can help to prevent damage from UV radiation. [16] Creases and abrasions may also form on scroll paintings from repeated rolling and unrolling, squeezing the scroll or tying the cord too tight. Screens can become distorted from uneven tension between the back and front side panelsCite error: There are <ref> tags on this page without content in them (see the help page).

Lacquer
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There are a variety of lacquers that have been, and continue to be used such as Urushi (unprocessed lacquer), Guangqi (processed), Nitrocellulose, lacquers with acrylic resins, and water-based lacquers, but the most well known lacqueris Urushi lacquer.[14] This lacquer paint is made from raw lacquer or sap taken from trees. It is then heated, filtered, and applied in thin layers to supports such as wood or metal. The lacquer is left to cure before it is polished, and another layer is added. The number of layers may vary, and each can be left in its natural transparent state, or colored with pigments to create Lacquer painting. While lacquer is a hard material, it is susceptible to cracks and loose joins from fluctuating temperatures and relative humidity. Extended exposure to light can also cause lacquer to lose its durability.[17]

Latex Paint
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Latex Paint (Also See Acrylic Paint)

Oil paint
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Oil based paint consists of pigments mixed into drying oil with various other ingredients that can be mixed in, and conditioned in several ways to modify its various properties and drying. Oil paint can be durable, but is still vulnerable to cleavage, excessive cracking, lifting, and flaking. Oil paint is more susceptible to damage in low relative humid conditions, and fluctuations can create stresses in the paint layers.[1]

Pastels
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There are two types of Pastels. Pastels that are made of pigment particles bound together with a binding agent, and oil pastels that have pigments mixed with wax and non-drying oil. Pastels that are pigment particles bound together take on a more chalky and loose powdery characterization, and are secured to its supports using fixative or diluted resin in solution. Oil pastels never fully dry, and are sensitive to scrapes, dust and dirt. Using a glaze over the surface can help to protect the oil pastel. [1]

Watercolor and gouache
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Water color and Gouache paintings are pigments mixed into water-soluble gums that are applied onto paper or rigid board supports. Due to its thin washes and light colors, watercolor paintings are very light sensitive. Also, due to their exposed support they are vulnerable to damage from dirt, dust, and pollutants.[1] Gouache paintings can form layers like acrylic and oil paint, but is still vulnerable to the same agents of deterioration as watercolors.

Painting supports and painted surfaces

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Because the material that makes up the support can have a major impact on the overall deterioration of an artwork, it can determine the best method for handling, storing, and displaying an object.[1]

Architectural structures (i.e. walls & ceilings)
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Architectural Structures (i. walls, ceilings)

Canvas
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Canvas Linen, hemp, jute, burlap, and cotton. [18]

Ceramics
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Ceramics vary widely in their construction, style, and use. There are three types of ceramic objects. They are earthenware, stoneware, and porcelain. Each of these types of ceramic objects are fired at different degrees and come in different colors. [19] The materials used in their construction are often a clay body, and some times mixed with sand, shell, chalk, mica, and ground-up fired ceramics. The surface of these ceramic objects are finished with glaze and fired in a number of ways. Decorations with gold, paint or enamel are applied over the glaze. These overglaze decorations are susceptible to abrasions or chemical damage from cleaning and handling. A ceramic object is also vulnerable to weeping and crizzling from fluctuations in relative humidity and temperature.[20]

Cloth or textiles
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Cloth or textiles are typically made from natural fibers such as wool, silk, cotton, linen, and hemp. However, some textiles more recently have been created with modified natural fibers such as Rayon. Textiles can make up many different objects from cushions to dresses. All with varying degrees and types of degradation. Light typically causes dyes to fade, and some fibers (silk) are more sensitive to physical damage from light. Low light levels are recommended to prevent damage. Mold and mildew caused by high levels of humidity and improper storage can cause irreversible damage. Damage can be mitigated with proper relative humidity levels and storing of textiles in acid-free tissue or clean cotton sheets. Textiles are especially vulnerable to attacks from pests such as moths and silverfish.[19]

Glass
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Paintings on Glass are particularly challenging because of first the fragile nature of glass, and second the smooth surface of glass that makes it difficult for paint to adhere to the surface.[21]

Ivory
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Paintings on Ivory are typically small, and the most commonly used paints were (watercolor, tempera, and gouache) directly on the surface of the ivory. The ivory was usually thin, translucent in appearance, and typically attached to a secondary support made of paper or card. Miniatures of these designs were frequently sealed in metal lockets or cases. The paint on the surface of ivory is very delicate and can be easily rubbed off, small amounts of water (breath, condensation or residues from cleaning) can affect the image. Ivory is also very sensitive to environmental changes. Ivory supports can be prone susceptible to warping and splitting from fluctuations in relative humidity.[22]

Metal
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Metal Various types of metal plates have been used as supports for paintings. These include: "silver, tin leaf, iron with tin on either side, copper, or copper coated with silver, tin, lead, or zinc. Enamel paint has been used on copper, but typically oil paint was used on metal supports. Metal does not respond to changes in relative humidity by expanding and contracting. However, metal can corrode over time staining paint or creating eruptions and flake in the paint. [22] It is also susceptible to physical deterioration such as dents, tears, and scratches.[19]

Outdoor murals
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Outdoor Murals

Paper
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Works of art on Paper range from watercolor paintings, prints, posters, and drawings using a variety of media from watercolor, charcoal, pastels, and colored inks. Due to the fibers in its construction, paper is vulnerable to various types of damage. Paper is easily torn, creased, or stained during handling. When exposed to light colors fade and the paper itself can discolor too. Works of art like watercolors and Japanese prints are especially vulnerable to fading. High relative humidity can cause paper to swell making it appear wavy or winkled. When exposed to long periods of high humidity, mold can form.[23]

Wood
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(Furniture, Panel, Lacquer Painting, Stretcher Bar, Wood Block Prints)

Wooden supports depending on what kind of object they are used for are made from hard and soft woods. Some types of woods that artists use are poplar, beech, spruce, pine, chestnut, cherry, mahogany, and cypress. Wooden supports are susceptible to several kinds of deterioration. These include insect infestation, fluctuations in humidity/temperature causing warping and cracking, and structural damages. Cradling was previously used to correct warping by thinning the original structural support and then adhering the cradle to the reverse side of the support. However, it has become widely understood that cradling can be harmful to the paint and ground layers. Conservators today instead work to preserve what remains of the wood support rather than making corrections. [24]

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Materials Recommended Relative Humidity Levels Potential Damage Recommended Light Levels Potential Damage Recommended Temperature Levels Potential Damage
Acrylic[25] 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.
Egg Tempera Example Example Example Example Example Example
Enamel 50 ± 10% High temperature sensitive max 300 lux Too much light creates heat and causes damage 68°F ± 2° High temperature sensitive[26]
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 [26]
Frescoes Example Example Example Example Example Example
Scroll/Screen Paintings 40-50% Example Example Example Example Example
Lacquer Paintings [14] 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
Oil Paint[27] 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°
Watercolors & Gouache 50 ± 5% Binder in paint can become friable[26] max 50 lux Color fade and discoloration 68°F ± 2° Deterioration of binder
Canvas 50 ± 10% Collects dust easily max 200 lux 68°F ± 2° Collects dust easily[26]
Ceramics[19] 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.[20]
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 [8]
Glass[19] 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[20]
Ivory[22] 35-55%[19] 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
Metal[19] 40-50%[22] 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.
Paper[19] 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.
Wood 45-50%[28] Warping, cracking, shrinkage, swelling max 200 lux High light levels can increase temperature causing warping, cracking, and shrinkage 20°F ± 2°[26] Warping, cracking, shrinkage, swelling

Tools used for conservation treatments and preventative care

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Infrared reflectology
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Conservators use infrared lights to see what lies directly underneath the surface of paint layers. This tool can help conservators identify previous restoration treatments, where damage was restored, changes in the paintings composition, and any underdrawing.[18]

  • Multispectral Imaging
  • X-radiography
  • Radiography penetrates entirely through the painting. Including the canvas, and wood panels or stretcher. Conservators can use x-radiography to find changes in composition, previous restoration treatments, and how the paintings support was constructed.[18]
  • X-ray fluorescence
  • Scanning Macro-XRF & Neutron Activation Autoradiography (NAAR)
Ultraviolet/visible fluorescence
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UV lamps are used by conservators to be able to identify pigments, varnishes, and retouchings from previous restoration treatments. It is limited to the upper layers of the painting.[18]

Conservation treatments and processes

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After determining an artworks condition, stability, history of previous restoration, and documenting and photographing the examination, future conservation treatments can be determined. The results of conservation treatments often yield a more "stable paint layer and support, more appropriate aesthetic presentation through cleaning, and a more unified paintings through the reintegration of the paint losses. It is not possible to restore a painting to its original form, but with careful preservation, documentation and restoration, conservators can help to extend the life expectancy of a painting." These treatments depend on the materials that make up an artwork. They can include:

Consolidation

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Securing areas of loose paint with adhesive.

Cleaning

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Removing or reducing "dirt, grime, discolored varnish, and retouching with solvent mixtures or mechanical means."

Facing

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Securing the paint layer with tissue and adhesive before corrective structural procedures.

Transferring

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Involves removing the original canvas or wood support, leaving the paint and/or ground layer, and re adhering the layers to a new support.

Cradling

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Cradling involves applying a wood latticework on the backside of a panel painting to prevent warping. Before cradling, the wood support is typically thinned.

Lining

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The lining of paintings is adhering a new canvas to the reverse side of the original canvases for added support.

Lining Removal

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Removing the old lining of a canvas because the adhesive has failed and resulted in delamination between the original canvas and the lining canvas.

Varnishing

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Applying "saturating varnish of either a synthetic resin or a stabilized natural resin varnish."

Filling

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Adding "putty-like material to areas of paint loss."

Inpainting

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Inpainting is applying synthetic or natural resin medium restoration paints to areas of paint loss to restore the "visual unity" of the painting.[18]

References

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  1. ^ a b c d e Institute, Government of Canada; Canadian Heritage; Canadian Conservation. "Know Your Paintings – Structure, Materials and Aspects of Deterioration – Canadian Conservation Institute (CCI) Notes 10/17". canada.pch.gc.ca. Retrieved 10 April 2017.{{cite web}}: CS1 maint: multiple names: authors list (link)
  2. ^ a b c Institute, Government of Canada; Canadian Heritage; Canadian Conservation. "Basic care – Paintings". www.canada.pch.gc.ca. Retrieved 10 April 2017.{{cite web}}: CS1 maint: multiple names: authors list (link)
  3. ^ Paintings Specialty Group Listserv. (2014). Backing Boards (M. Gridley, Ed.). Retrieved March 27, 2017, from http://www.conservation-wiki.com/wiki/Backing_Boards
  4. ^ Swain, L. (2010). Museum registration methods 5th edition. Washington, DC: The AAM Press, pg. 298.
  5. ^ Neilson, D. (2010). Museum registration methods 5th edition. Washington, DC: The AAM Press, pg. 212.
  6. ^ Fisher, G. (2010). Museum registration methods 5th edition. Washington, DC: The AAM Press, pg. 286.
  7. ^ Michalski, S. (2016, August 4). Agent of Deterioration: Incorrect Relative Humidity. Retrieved March 29, 2017, from http://canada.pch.gc.ca/eng/1444925238726
  8. ^ a b Bachmann, K (1992). Conservation Concerns: A guide for collectors and curators. Washington D.C.: Smithsonian Press.
  9. ^ Landrey, G., & Hoag, R. (2009). The Winterthur Guide to Caring for Your Collection. University Press of New England.
  10. ^ Government of Canada; Canadian Heritage; Canadian Conservation Institute. (2016, July 22). Agent of Deterioration: Pollutants. Retrieved April 04, 2017, from http://canada.pch.gc.ca/eng/1444924955238#pollu7
  11. ^ Smithsonian Museum Conservation Institute. (n.d.). Caring For Your Paintings. Retrieved March 28, 2017, from https://www.si.edu/mci/english/learn_more/taking_care/care_painting.html
  12. ^ Winter, S. D. (2010, November 15). Conservation problems with paintings containing fluorescent layers of paint. Retrieved April 07, 2017, from http://ceroart.revues.org/1659#tocto1n2
  13. ^ Art Conservation at the University of Delaware : Egg Tempera. (n.d.). Retrieved April 05, 2017, from http://artconsweb-002.art-sci.udel.edu/about/kress/historic-materials-technical-terms/egg-tempera
  14. ^ a b c d e Ward, G (2008). The Grove Encyclopedia of Materials and Techniques in Art. New York: Oxford University Press.
  15. ^ Learner, T. J. (2005). Analysis of modern paints. Los Angeles, CA: Getty Conservation Institute.
  16. ^ Melching, S. (2013, May 24). How to Care for Japanese Scrolls & Screens. Retrieved April 8, 2017, from http://denverartmuseum.org/article/staff-blogs/how-care-japanese-scrolls-screens-part-1-2
  17. ^ Laurin, G. (2013, January 9). The Craft and Care of East Asian Lacquer. Retrieved April 08, 2017, from http://denverartmuseum.org/article/staff-blogs/craft-and-care-east-asian-lacquer
  18. ^ a b c d e Ocon, N. (n.d.). A Primer for the Materials, Methods and Techniques of Conservation [PDF]. North Carolina Museum of Art. http://ncartmuseum.org/pdf/conservation-primer.pdf
  19. ^ a b c d e f g h Henry Francis Du Pont Winterthur Museum (2000). The Winterthur Guide to Caring for Your Collections. Delaware: University Press of New England.
  20. ^ a b c Government of Canada; Canadian Heritage; Canadian Conservation Institute. "Care of Ceramics and Glass". Canadian Conservation Insittute. Retrieved 10 April 2017.{{cite web}}: CS1 maint: multiple names: authors list (link)
  21. ^ Winterthur Museum. "Paintings Conservation". Winterthur Museum, Garden & Library. Winterthur Museum. Retrieved 10 April 2017.
  22. ^ a b c d Government of Canada; Canadian Heritage; Canadian Conservation Institute. "Care of Paintings on Ivory, Metal and Glass". Canadian Conservation Institute. Retrieved 10 April 2017.{{cite web}}: CS1 maint: multiple names: authors list (link)
  23. ^ Government of Canada; Canadian Heritage; Canadian Conservation Institute. (2016, December 07). Basic Care - Works of art on Paper. Retrieved April 09, 2017, from canada.pch.gc.ca/eng/1454534476494#a1c
  24. ^ Art Conservation at the University of Delaware : Wooden Supports. (n.d.). Retrieved April 05, 2017, from http://artconsweb-002.art-sci.udel.edu/about/kress/historic-materials-technical-terms/wooden-supports
  25. ^ Government of Canada; Canadian Heritage; Canadian Conservation Institute. (2016, April 18). Environmental and Display Guidelines for Paintings. Retrieved April 08, 2017, from http://canada.pch.gc.ca/eng/1439925170465
  26. ^ a b c d e Southeast Conservation and Restoration. "Recommended Environmental Conditions for Museum Objects". Southeast Conservation and Restoration. Retrieved 10 April 2017.
  27. ^ Fahey, M. (2016). The Care and Preservation of Oil Paintings. Retrieved April 8, 2017, from https://www.thehenryford.org/docs/default-source/default-document-library/the-henry-ford-oil-paintings-conservation.pdf?sfvrsn=2
  28. ^ Scharff, M., & Staniforth, S. (2015, September 22). Temperature and Relative Humidity: Agents of Deterioration. Retrieved April 09, 2017, from https://www.iiconservation.org/sites/default/files/news/attachments/6668-iic-itcc_2015_ppt_temperature_and_relative_humidity_mikkel_scharff.pdf