The materials that make up the paintings such as base, primer, paint and varnish layers differ in their mechanical and physicochemical properties. As a result, they react differently to changes in temperature and relative humidity of the environment. Since the paint layer coated with varnish is waterproof, the reverse side of the painting, its base, reacts to changes in humidity in the first instance. Wood, canvas and paper being hygroscopic materials contain moisture, the amount of which is determined by the environment.
The level of relative humidity (hereinafter RH) of the air that ensures the good preservation of oil painting is 50-60% at a temperature (t°) of 17-19° C. Optimal parameters for exposing tempera painting are RH 50 ± 5%, tо 18 ± 1° C.
When the relative humidity rises (more than 70-75%), the canvas is no longer in the state of normal tension. Prolonged exposure to such an atmosphere can lead to deformation of the canvas, swelling of the glue contained in the primer, and the appearance of mould. Often, mould formed in the primer penetrates through micro cracks into the paint layer and becomes noticeable on the front side of the painting. The glue loses its adhesion properties, the bond between the primer and the base is broken, and peeling of the paint layer appears. Duplicated canvases start peeling off. With moisture, the optical properties of the varnish change: a network of tiny cracks forms in it; it becomes cloudy, then turns white and loses its transparency.
High temperature (25-30° C) and dry air (RH less than 50%) lead to drying out of the canvas fibres. As a result, the canvas gets less elastic and less durable. The primer becomes brittle. Its fractures are transferred to the paint layer, and craquelure is formed. All this may lead to lagging and shedding of the paint layer with the primer.
Wood bases react very quickly and unfavourably for the preservation of the painting to changes in temperature, and especially relative humidity. Sharp fluctuations in the atmosphere cause rapidly alternating contractions and expansion of the base accompanied by deformation of the wood, its warping and ruptures. The movement of the base in this case inevitably causes a corresponding tension of the primer and the paint layer.
One of the factors that directly affect the preservation of paintings is light. In a dark room, the coating of the oil-lacquer film and oils turn yellow causing a general darkening of the painting. In a bright room, light can adversely affect the artworks exhibited there, and the damage caused by its impact can be significant.
Under the impact of light, both natural and artificial, two types of destruction occur: visible - a change in shade or colour and invisible - structural destruction or changes in the physical properties of materials.
During the exposition, paintings on canvas require technical devices to ensure their best preservation. The installation process consists in making stretcher bars and properly stretching the canvas on then ensuring that the painting fits the frame. In addition to the preservation of the painting, it should also contribute to its aesthetic perception.
The frame used to display the painting, in addition to aesthetic functions, has also protective ones. The painting should not fit tightly into the frame. Depending on the size of the painting, there should be a gap of 1-3 cm between the painting and the grooves in the frame. This distance is necessary in case you have to wedge the stretcher bars in the future to adjust the canvas tension. The painting should not be fastened to the frame with nails; it is better to use wooden or metal clamps.
The hanging of paintings in exhibition halls should be reliable and convenient. For this, special rods are fixed at some distance from the walls. It helps to avoid spoiling the wall with nails and to easily move the paintings to other places on the walls. The paintings are hung on cords, soft wire or thin steel cables. The cord is threaded through the rings screwed into the frame and tied in a knot either at the painting or at the bar.
There are other ways to hang pictures on a bar, for example, using hooks. To make the painting inclined, the rings are screwed into the side planks at a distance equal to 1/3 of the height of the painting from the top edge. It’s not recommended to hang paintings especially large ones at a high angle as it lead to sagging of the canvas. It is forbidden to screw rings or hammer nails into the stretcher bars. To prevent the paintings from touching the wall in order to avoid cooling, dampness, as well as to ensure better air circulation between the wall and the exhibit and to soften the effect of wall vibrations on the painting, cork gaskets are attached to the bottom of the frame on the back, which makes it possible to move the lower edge of the frame by 2-4 cm from the wall. Paintings should not be hung near radiators, ventilation openings and vents.
Speaking of graphics, we mean not only drawing, engraving and lithography, but also watercolour, gouache, pastel, i.e. an image made on paper. Graphic sheets are extremely sensitive to changes in temperature and humidity conditions.
The optimal microclimate parameters for exhibiting graphic works are as
The limits of permissible parameters are slightly wider; in this range
there are no irreversible changes in materials:
Temperatures above + 24° and relative humidity below 40% lead to dehydration of the work and its mechanical damage; RH above 65% leads to the danger of bio infection. The combination of + 24° C and RH 65% is only permissible for very short periods of time.
While storing and exposing graphics, it is necessary to take into account not only temperature and humidity but also the speed of air flows, which should not exceed 0.1-0.2 m per second, and the air exchange should proceed gradually without sudden jumps. It is also advised to avoid direct air flow onto the exhibits.
The lighting of exhibits is of great importance. Natural and artificial light consists of visible light as well as UV and IR components. When protecting exposed works, we must strive to eliminate damaging UV radiation, minimize thermal IR, and limit the visible light.
Damage caused by light, i.e. fading of paper and paint, is virtually irreversible. UV exposure is especially dangerous for watercolours, because paint contains extremely small particles of pigment, which lie on the surface of the material and fade very quickly. Thus, we may observe the photo destruction of the base: yellowing, a decrease in mechanical strength and an increase in fragility. Literally after 3 months, the paper base loses up to 60% of its strength.
The admissible limit of illumination for graphic works is 30-50 lux, which can be correlated with the illumination of the basement or bright moonlight.
Bear in mind that the same degree of damage to an artwork can be the
result of both short-term strong radiation, as well as weak, but
100 lux x 5 hours = 500 lux/h
50 lux x 10 hours = 500 lux/h
If you expose a graphic work for 10 hours at an illumination of 300 lux, changes in colours will be noticeable after 17 days, if at 50 lux, then only after 100 days. With a total annual illumination intensity of 1.5 million lux/h, the practical life of works unstable to light is 20 years. In the absence of UV radiation, this period increases 6 times. Considering all these factors, the exposure period of prints, watercolours and other similar objects should not exceed three months.
In order to preserve artworks, the lighting during an exposition should be as low as possible – to the extent the comfort conditions permit it - and last as short as possible.
A common type of mount for graphic art is a mat consisting of a substrate and a cover with a window. If it is not possible to obtain special cardboard, you should strive to get the best quality white cardboard as soon as possible. If the artistic solution requires a coloured mat, for example, bright blue or red, then the mat should be two-layer (only the outer part will be coloured), or the reverse side of the mat, which is in contact with the original needs to be laid or glued with white paper, possibly white Whatman paper of good quality. In any case, the backing should be white paper or cardboard.
Graphic works decorated in a mat are placed under glass in edging or frames for exposure. Works made in the technique of pastels, charcoal, sanguine, as well as fragile miniatures on bone and parchment are constantly kept in edged form.
When determining the preservation degree of the sculpture it is vital to check the structural solidity of the stone and the state of its surface. The natural physical and mechanical defects of the stone material include structural heterogeneity, i.e. layering and loose inclusions.
For exposing sculptures, the optimal storage regime is as follows: tо 18-20° С, RH 55-60%. Daily fluctuations in temperature should not exceed 1° C, and humidity - 5%.
Many people refuse any preventive work to clean the sculpture for fear of damaging the patina. The main argument in favour of such a “hands-off attitude” usually comes down to the fact that contamination is an integral part of the patina, and therefore must be preserved. The fallacy of this attitude becomes obvious if we remember that the natural patina is a chemically resistant product, homogeneous to stone material and organically associated with it. Mechanical impurity is alluvial substances of various origins chemically not associated with stone, but capable of entering into active interaction with it under certain conditions.
Impurities getting on the surface of the sculpture and being held by electrostatic forces, moisture and diffusion in the pores of the stone become more and more persistent and difficult to remove. As a result, chemical and biological products appear and penetrate into the pores of the stone thus destroying it.
Thus, underestimation of measures for the timely cleaning of the sculpture from contamination and the use of too active cleaning and detergent preparations affect the safety of the sculpture in equally negative manner.
To maintain comfortable conditions for glass exposure, please follow
1. t° – 20°С, RH 30-40%;
2.isolation from bright daylight; for example, when a transparent glass containing manganese oxide is exposed to sunlight for eight days, it darkens;
3. keep at distance from incandescent lamps;
4. exhibits are to be placed in showcases, which must ensure air exchange.
It is not recommended to place showcases near windows; you should refuse to use lighting devices (point light) in showcases. Even slight local heating can destroy an exhibit in a short time.
The main recommendations for the installation of glass objects can be as
1. A showcase intended for displaying glass must have a podium that prevents vibrations.
2. A showcase must completely protect the exhibits from dust, but not be absolutely sealed (gas exchange is important for glass).
4. If a rigid fixing fastener is recommended for exposure, then soft spacers are required.
6. When exhibiting glass works (given its extreme fragility and the complexity of restoration), it is not recommended to hang other exhibits over them.
7. Any illumination with a point source of radiation inside and outside the showcase should be avoided.
8. If the relative humidity exceeds the recommended values, it is advisable to place silica gel in the showcase.