Anatomy of a Painting
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The responsibility for the arts longevity begins with the artist's choice of materials and the techniques of construction. Some materials or their method of application can cause problems that can never be remedied by conservation or restoration treatments.
Materials mixed and applied in a different manner than the manufacturer recommends, may develop problems. These types of problems usually occur with innovation. Established artists most often have already dealt with material and technique problems.
When artists still apprenticed to a master painter, they were taught the preparation, materials and compatibility. Even then some combinations have not stood the test of time. Today, the artist learns the techniques of creating art, but very little about the chemistry of their media. Many artists never consider longevity, or what future problems unusual materials might cause.
For you to properly care for your art, you must understand its basic construction. This is not as difficult as you may think; most art is just common materials put to gather in an uncommon fashion. Knowledge of the construction will allow you to make an informed examination of your collection.
The traditional construction of a painting on canvas is to stretch a canvas on expandable bars. These stretcher bars are the foundation for the painting. It is important that these bars be designed to expand unevenly so they may be expanded to compensate for the canvases stretching. Canvas, like all woven materials, has a warp and weft: the difference in the direction of the weave. Most weaves will stretch more in the warp direction, than in the weft, so stretcher bars must expand at an unequal rate so that they may be "keyed out"--i.e. additional tension applied to the canvas in both directions placing equal tension on the threads of the weave in both the warp and weft directions, and to keeping it taut.
Traditionally a canvas was stretched and then sized with one or more coatings of hot water soluble glue. This sealed canvas shrunk the canvas making it titer on the stretcher bars
then one or more coats of a gesso ground was applied. This ground coating was also used on panels; it created a smooth surface eliminating the wood texture or the canvas weave. This ground was water-soluble and likely lose its attachment to the panel or canvas if exposed to water or high humidity. Water may also cause a canvas to shrink; wood panels may warp or crack.
An artist applies paint, defines areas and builds colors, adds highlights, all changing the consistency of the paint. It will be thin in some areas and thick in others, when it dries, this difference will affect the visual concept and color.
The life of a canvas depends on the type of fiber and its care. Burlap or jute will most often deteriorate before a good cotton canvas; linen will last even longer. As a canvas ages, it becomes dry and brittle, and becomes more susceptible to damage by contact. It is at this time that a lining is done. It is always better to do this as a conservation measure than to wait until a hole or tear makes restoration necessary.
We see color as light it is reflected from a surface, if the surface is dull and non reflective our perception of color will be less. It is important that the surface is consistent and a good picture varnish creates that consistency. Varnish also protects the painted surface so the accumulation of smoke and dirt rests on the varnish coat, not on the paint itself.
Picture varnish for paintings is formulated for their protection and for easy removal; using any other type of varnishes may cause damage that cannot be repaired. The application of other substances can also be damaging, oils, especially linseed oil, creates a tacky surface that collects more dust and dirt then dries hard. Paintings should never be re-varnished without first having their surface cleaned. Varnishing a dirty painting only obscures the art.
Looking at a dirty painting or one with a heavy yellowed varnish is like looking at the art through sunglasses. The true colors of the art as well as its perspective maybe significantly diminished.