Hi,
Let me first apologize for taking this so far away from the original topic. The conversation made me curious about the preservation of pastels. I did a little research and found the following article to be very useful. I will reference it's source (I hope that covers copyright infringement?) Anyway here is what I found:
Pastel Conservation
The following article was taken from a lecture given by Ross Merrill on October 4 at the 1997 IAPS Convention at Kansas City, Missouri. Mr. Ross Merrill has served as the Chief of Conservation at the National Gallery of Art, Washington D.C. (USA) for the past 15 years.
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http://www.capecodpastelsociety.com/conservation.html):
During his presentation, Mr. Merrill presented current research on conservation of pastel paintings in order to inform artists in their choice of materials, both for archival quality and user safety. Mr. Merrill assumed the position of "devils advocate; providing basic facts about the medium and dispelling myths. His concern as a conservator is for the "long term", for the work's ability to withstand the test of time. It is his position, therefore, to assume the worst possible conditions and to attempt to preserve the work in the best possible condition.
There are four components to a pastel painting: Support, Pastel Layer, Fixative Mounting.
One of the important tasks for the National Gallery is to preserve art works during shipping. A painting packed for shipping must be able to withstand 50 g's of force, the equivalent of dropping it from 36' onto concrete, the same distance from the tailgate of a truck to the ground. However, tests completed at the National Gallery have shown that pastels will only withstand a force of10 g's. This is the equivalent g force to dropping a suitcase on the airport floor. According to Mr. Merrill, "Any more than 10 g's, and some pastel pigments will be dislodged."
Other factors figure into this formula. When a pastel is not firmly attached to a backing material (for example, attached to linen or hung free), the amount of vibration the work can withstand is significantly less than the 10 g's tested for properly mounted works. The simple vibration from the road and motor of a vehicle will be enough to dislodge some pigment if the supporting material is free to oscillate within the crate. It is therefore important that pastels be firmly attached to a mounting surface.
Support: During the 18th century, pastels were applied to vellum or paper which was attached to a canvas. These pages were placed like tiles over the canvas and today the paper seams can be seen when viewing the images in a museum. Since then there have been many advances in pastel supports.
The support is the surface the pastel pigment is applied to. It is a mistake for a pastel painter who is concerned with fine quality work and superior quality pastel pigments to overlook the quality of the support. Further, there is nothing a conservator can do to preserve or repair a support which has deteriorated from the effects of acid. This condition is usually caused by poor quality support made from a wood pulp base. Since the buffering effect of calcium carbonate is exhausted over time, those supports which advertise neutral pH will eventually return to the natural acid condition of the stock.
Many of the supports manufactured today for pastel art are textured. Textured surfaces have become very popular in the last half of the 20th century, yet most of these supports are not of archival quality. Some researchers and conservators who work in pastels refuse to use textured surfaces because they believe the support is unstable.
Some artists believe it is possible to seal a pastel into a frame so tightly that oxygen can be excluded, but Mr. Merrill stated that oxygen can even penetrate the surface of Plexiglas. That being the case, nothing can protect the support from oxygen.
Mr. Merrill suggests that a serious artist who wants a textured surface should consider applying an acrylic followed by pumice to the surface of 100% rag paper. This should provide a stable support. In conclusion, he asserted that any support made from a wood pulp base will not have a long life.
Another problem of supports is lightfastness. Early supports of100% rag (colored before being made into paper) were very light fast. However, later developments in the treatment of supports with color have not proven as effective. Today, most supports are quite "fugitive" (subject to fading). It is important for an artist to know the lightfastness of a support which will showthrough the finished work.
Colorfastness can be tested. As an example, Mr. Merrill presented a test kit which uses the "British Wool Standard," blocks of British dyed felt used to determine the amount of light energy which reaches the support samples. Or items to be tested can simply be positioned in a studio's north window.
100% rag paper such as Reeves BFK can be treated with a lightfast watercolor pigment as a background tint. This technique, which uses an archival support with pumice should pose no problems for the longevity of the piece.
An inquiry from the audience was made about a new support called "Solid Ground." Mr. Merrill stated that this support is composed of poly vinyl chloride (pvc) and is susceptible to UV light. It is also the same material used in some plastic pipes and with time is subject to "off gassing." Supports such as masonite, plyboard, and pressboard are unstable. However, new treatments have become available which can be applied to the surface to provide a barrier coat to prevent the acids inside the board from altering the pastels or the base coat.
Pastel Layer: Fillers are designed to reduce the chroma of a pastel stick. Fillers make the pastel opaque. In the past, material such as Plaster of Paris, kaolin, alabaster, chalk, and titanium white were used. In the 19th century, it was understood that particular pigments were best combined with particular fillers, and so pastel makers experimented to find the best filler for each color. Today, a universal filler composed primarily of aluminum, kaolin, plaster is used.
It is interesting to note that the high quality of pastels being produced today has spurred a renaissance of the medium. At the beginning of this century, pastels declined in quality and the medium suffered in popularity. In the past, discriminating artists often made their own pastels, but today manufactured materials are of such high quality that is no longer necessary.
Another issue of lightfastness is in the pigments themselves. Pastels are pure pigments applied to a support. A rule of thumb for the artist is that the thicker the layer of pastel, the less susceptible it will be to fading. The problems occur when the coating is thin. In oil or watercolor painting, the glazing coat shows the most fading over time. Also in oils or watercolors, there is a binder which helps reduce the effects of ultraviolet light on the pigments. Although binders in oil paints tend to darken pigments, they also tend to protect them.
Due to the issue of lightfastness, the pastel artist should take care to select colors which show the greatest resistance to fading. Each manufacturer publishes a chart which shows the relative lightfastness of their pigments. These ratings do not yet compare the products of different companies. The American Society for Testing Materials (ASTM) tests oils and watercolors. Mr. Merrill hopes that soon there will also be a standard for pastel pigments.
The pastel artist needs to be aware that there are some synthetic dyes and pigments on the market. Most of these are coal tar derivatives which are no longer used in mainline pastel products, but in some are found in cheaper pastels and pencils. These aniline dye-type pigments are notoriously fugitive.
Binders control the hardness of the pastel stick. The more binder used, the harder the stick. The binder, however, has nothing to do with the way the pastel adheres to the surface of the support. The binder has no effect on the pigment beyond holding the stick together.
Early pastels were made of either pure pigment or natural chalks. The definition of a pastel is a pigment which has been purposely made using binders. Chalks are natural. A few of the binders used in the past were gum arabic, honey, and sugar water.
The most common binder today is methyl cellulose. Gum arabic will give a harder pastel, but it will tend to mold and yellow with time. Methyl cellulose is not susceptible to mold or yellowing.
In oil pastels, the binding agent is either wax or oil. Oil pastel sticks have less wax.
Fixatives: Another problem is fixing pigments to the support. Unfixed pastels are easily smudged and should be framed immediately. Some artists of the past considered pastels to be only temporary expressions of art.
In the past, some artists fixed pastel artwork by placing a piece of paper over it and burnishing the pastel down into the support. According to Mr. Merrill, it is amazing how well the technique works.
Most of the pastelists from previous generations used fixatives. Degas used fixatives. His favorite was alcohol and white shellac. Today there are a number of alternatives. Krylon Acrylic Varnish B72 is used by conservators. This product will remain unchanged for 400 years, but does have a tendency to saturate the surface. Grumbacher B77 varnish or "tough film" is the same as B72, but will not saturate. Krylon workable fixative and Sennelier fixative are both good products. One should stay away from Grumbacher's"blue label" fixative.
Mr. Merrill stated that no matter what the condition of the pastel when in enters the conservation laboratory, it will be fixed before it leaves. Almost all pastels from the past have been fixed. This procedure will continue. Be assured that if your works make it to any museum, they will be fixed.
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