Preservation techniques for oil paintings

Preservation skills of oil paintings

From the moment the artist paints, the protection work of oil paintings has actually begun. Here are some tips for the preservation and maintenance of oil paintings. I hope it will be useful to everyone. Help!

1. Light intensity

Light intensity refers to the intensity of light, measured by the energy of visible light received per unit area, referred to as Illuminance, unit lux (Lux or Lx).

Light can cause serious and irreparable damage to oil paintings. Excessive light intensity will cause the oil painting to fade or darken. Some oil paintings will darken so severely that the image and details will be blurred or even disappear. In order to avoid damage caused by light, oil paintings should be displayed in a dark area that is not exposed to direct sunlight. The recommended light intensity is within 200Lux.

Excessive light can also cause excessive heat accumulation, causing damage to the oil painting. Therefore, you should avoid placing lighting lamps near paintings, such as installing commercial lamps on the tracks of the exhibition hall, or placing them directly above them. Diffused spotlights should be installed at least 10 feet away from the painting to avoid potentially damaging heat buildup.

Oil paintings usually need to be less illuminated during display. It is necessary to add appropriate display lighting and a timer, or to limit the overall exposure time of a collection in a year. Collections that are particularly sensitive to light should have annual exposure limits. The amount of light received in the warehouse should not exceed 50Lux, the ultraviolet rays should not exceed 75μW/lm, preferably less than 30μW/lm, and it should be kept in darkness most of the time.

2. Temperature and humidity

Excessive temperature and humidity and severe temperature and humidity fluctuations will cause the wood and fiber components of the oil painting to expand and contract, thus causing damage to the oil painting. Wood and fibers absorb moisture very easily, with the material expanding in a humid environment and shrinking in a dry environment. Oil paintings are notoriously inflexible, and the expansion and contraction of the underlying wood and fiber structure may result in cracking or peeling. This dimensional change can cause the canvas to relax and sag in the winter.

If the temperature at which oil paintings are stored is too high, the base materials of the oil paintings will be damaged, causing their materials to undergo thermal degradation, thermal oxidation, hydrolysis and other reactions faster, leading to dryness, brittleness, discoloration and other conditions. . When the temperature reaches 40°C, the asphalt-containing pigments in the color layer may be dissolved, forming dark brown stains and contaminating the picture.

Humidity instability has a greater impact on oil paintings than temperature instability. The level of humidity is obviously reflected in the expansion or contraction of the oil painting. Since its components have different expansion coefficients, serious consequences may occur. The bases of oil paintings, such as linen, wood board, and cardboard, all have strong water absorption. In particular, the fabric base is extremely sensitive to dry and wet reactions, while the base and color layers react relatively slowly. The canvas expands immediately after getting wet, and shrinks again when the relative humidity decreases. At this time, the tension on the back of the canvas increases significantly, while the tension on the front of the colored layer does not change significantly. This kind of shrinkage and expansion of the canvas and the restriction of the shrinkage and expansion of the canvas by the base and the pigment layer often form an unbalanced force, causing the base and the color layer to partially bulge due to their separation from the base. The intuitive phenomenon is cracks in the picture. Lifting and peeling of oil paint.

The same is true for the damage caused by unstable humidity to oil paintings on wood panels. When the relative humidity is high, because the color layer of the picture has a certain blocking effect, more moisture enters the painting body from the back of the wood board; when the relative humidity decreases and the wood board painting dries, the moisture is also more likely to evaporate from the back side. As a result, the back side of the wood-panel oil painting shrinks much more than the front side, causing the oil painting base to form a convex curve. In order to adapt to this bending deformation, the paint layer may crack.

Among the various factors that are not conducive to the preservation of oil paintings, moisture is the most damaging. In addition to causing the object to expand, it will also contribute to the destructive effect of light, promote pigment changes, cause fading, accelerate the oxidation of cadmium, strontium, titanium, lead and other pigments, causing the oil in oil paints to turn yellow and white. . Moisture is also an important condition for mold growth. The optimal relative humidity for mold growth and reproduction is 70% to 80%. Therefore, the upper limit of relative humidity in oil painting warehouses cannot exceed 65%, and the optimal humidity in the south should be around 50%.

Most oil paintings on canvas are protected by elastic wooden frames with extendable and contractible functions. This wooden frame stretcher is equipped with an expandable elbow interface that can be adjusted to ensure that the oil painting remains appropriately tension. The joint can be expanded by pushing small wooden wedges into the inside corners of the back of the painting.

The exhibition and storage environment of oil painting collections must be strictly monitored to maintain appropriate temperature and humidity, and control fluctuations in temperature and humidity to a minimum.

Acceptable temperature and humidity levels for the preservation and display of oil paintings are as follows:

Winter temperature 65-70 degrees Fahrenheit (18-21°C)

Relative humidity 40%-45%

Summer temperature is 70-75 degrees Fahrenheit (21-24°C)

Relative humidity 45%-55%

Use thermometers and hygrometers to store and display oil paintings Monitor and strictly control the temperature and humidity of the environment. At the same time, excessive temperature and humidity and violent fluctuations in temperature and humidity should be avoided. Make sure the oil painting is kept away from heat sources and out of direct sunlight.

In fact, the basic requirements for choosing a storage place and location are safety and easy access, keeping away from fire sources, heat, water pipes and heating pipes, and avoiding hanging paintings on exterior walls with large temperature and humidity differences. Under normal circumstances, a certain temperature or humidity is not the main cause of damage to oil paintings, but the constant changes of the two. The storage space needs to minimize this change and keep it basically consistent with the temperature and humidity of the exhibition space. . If you use the basement as a storage space for oil paintings, the biggest problem you face is moisture. Excessive relative humidity often causes mold to grow, causing stains on the surface of the oil paintings. Therefore, the oil painting warehouse should avoid being located in the basement.

3. Dust and dirt

Dust and dirt on the surface of oil paintings are really unsightly. At the same time, these dusts also become a breeding ground for mold growth. Blurs the image of the oil painting. Accumulation of stains can cause discoloration of the picture.

After the oil painting is stored for a certain period of time or displayed for a period of time, some dust and dirt will accumulate on the surface, and it needs to be cleaned in time. Generally speaking, cleaning of oil paintings should be carried out by professionally trained staff. During the preservation process of oil paintings, some simple operating procedures can also be adopted to extend the life of oil paintings. You can use a soft-bristled brush to gently brush away dust from the surface of the painting and frame. You should be careful when sweeping away dust from oil paintings to avoid bending the canvas with excessive force or causing the paint to fall off due to impact on the oil painting. Oil paintings that have cracks and peeling marks cannot be dusted with a brush. The back of a painting should be cleaned by sweeping or vacuuming. To clean the back, the painting should be removed from the frame and placed face down on a clean surface. Excessive dust should be cleaned using a small soft-force nozzle with a brush. If the surface dust cannot be removed by sweeping, you can moisten a cotton swab with distilled water and gently roll it forward on the surface to remove the dust. It should be emphasized that if the screen has signs of peeling, no cleaning should be done.

Smoking should be strictly prohibited in oil painting warehouses and exhibition areas, because nicotine and soot can easily deposit on the surface of oil paintings, causing damage to the paintings. Therefore, smoking should be prohibited in the oil painting storage space to prevent the deposition of nicotine on the surface of the oil painting.

4. Pests

Insects that cause harm to oil paintings mainly include Dermestidae and mealybugs.

Dermatology generally relies on protein-based materials to survive. There are protein components in the glue of canvas, so we often find pests on the back of the oil painting between the canvas and the inner frame. If you notice holes in your canvas, the presence of worm-shaped insects, or insect carcasses, you can be sure you have a dermoid pest problem.

The most typical damage caused by mealybugs is the drilling of small holes (about 2 mm in diameter) in wooden materials. Therefore, the pest status of oil paintings during preservation should be checked regularly. If signs of intrusion are discovered, the object should be placed in a plastic bag, isolated, and professionally disposed of.

5. Human factors

The greatest damage to cultural relics is often caused by irregular operations. Therefore, when in contact with oil paintings, operators must be extra careful, beware of any behavior that is harmful to oil paintings, and properly preserve oil paintings. Especially the following links:

Moving: Before moving the oil painting, the operator must make sure to remove all jewelry, belt buckles, etc., so that the oil painting will not be accidentally torn or damaged when moving. scratches. When moving the painting, be sure to hold the two vertical sides of the painting. When supporting a painting, do not hold it by the top of the frame or its hanging wires. Also be careful to ensure that the metal hanging wire of the painting does not puncture the back of the painting during the move. Avoid hitting the canvas as even the slightest impact may cause future cracking of the surface.

Oiling: A warm and dry climate is required when applying varnish. Too high humidity can easily cause moisture in the air to enter between the varnish and the pigment layer, causing the varnish to turn white. Too low a temperature is not conducive to the normal evaporation of the solvent and will slow down the drying speed. In order to prevent the varnish from sticking to dust in the air, the space and work where the varnish is applied must be cleaned the night before so that the dust in the air can be clarified overnight. All tools and containers must be clean and free of moisture. You can choose to apply varnish by brushing or spraying. In principle, the effect of multiple thin layers is always better than one thick layer.

Storage: Most modern museums use some movable oil painting racks to store oil paintings. Oil paintings can be hung on mobile mesh racks. This method can ensure that the oil painting does not directly contact the ground, which is better than stacking. It can reduce the pressure on the oil painting, reduce friction on the surface of the work, and is also convenient for handling and viewing.

The oil painting stand can slide smoothly, protecting the frame and bottom border of the work from wear and tear. However, oil paintings should be stored in groups according to size. Large, medium and small sizes should be stored on different shelves to avoid uneven stress. Oil paintings should be hung vertically, with about 5-6 works in each group. Storing too many pieces on the same shelf can put too much pressure on them, so make sure the canvas frame tenons don't rest against adjacent paintings. Damage from stress is often not noticed right away, but will eventually lead to cracks and warping in the collection.

Protection: The most important thing to protect oil paintings is to protect the picture. If not protected, the surface of an oil painting can easily be scratched by hard objects or worn by adjacent works. The best way is to wrap it in acid-free cellophane to avoid dust contamination and light, and to prevent touching by hands. During the display process, the oil painting should also be protected from scratches by hooks, wires or other hanging materials, especially hard objects with protruding edges.

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