Irreversible Changes in Paintings

Trying to encompass the whole narrative of

paintings conservation in a single volume

might seem an impossible task

David Bomford

Art restoration is related to art conservation. To successfully care for cultural heritage, conservators must have an extensive understanding of the complex material and historical nature of objects.

Conservation involves the care and preservation of works of art, all of which are, over a period of time, subject to alteration and deterioration. This may be due to several factors: chemical, physical, and biological changes which occur through the inherent instability of the materials of an object, or

result from faulty technique; accelerated decay as a result of poor environmental conditions, mishandling, or accidental damage and deliberate intervention by owners or restorers. Changes in the states of materials are largely inevitable and irreversible but deterioration can be reduced by proper conservation treatment. This, however, demands sound knowledge of the historic and

artistic value of the object, as well as its chemical and physical structure.

There are reversible and irreversible changes, among the last we can single out such as craquelure, yellowing, pentimenti, color changes.

Craquelure (French: craquelé, Italian: crettatura) is the fine pattern of dense "cracking" formed on the surface of materials, either as part of the process of ageing or of their original formation or production. The term is most often used to refer to tempera or oil paintings, where it is a sign of age that is also sometimes induced in forgeries, and ceramics, where it is often deliberate, and usually called "crackle". It can also develop in old ivory carvings, and painted miniatures on an ivory backing are prone to craquelure. This may be visually disturbing but cannot be corrected.

Dutch researchers have shown that when old-master paintings are cleaned, larger molecules of aged varnish can be left behind which actually seem to contribute to theyellowingof canvases and panels. The researchers were able to study particles of varnish taken from more than fifty paintings by such Dutch masters as Rembrandt, Steen and Van Gogh. Yellowing occurs with all drying oils, such as linseed. It may cause color changes, particularly in pale areas and blues.

Pentimenti are alterations in a painting, evidenced by traces of previous work, showing that the artist has changed his or her mind as to the composition during the process of painting. The word is Italian for repentance, from the verb pentirsi, meaning to repent.

Charles S. Rhyne, the author of the book Changes in the Appearance of Paintings by John Constable, notes that:

?One of the things I should most like to know about 'The Leaping Horse' is whether or not Constable allowed the evidence of those changes to be visible when he showed the painting to fellow artists and

prospective clients. Although Constable increasingly retained evidence of the creative process in his paintings, my guess is that he never wished major compositional pentimenti to show in any finished painting, a point which we shall return to when considering changes wrought by time and

conservation. It seems at least possible, however, that Constable never considered this painting, and perhaps others, quite finished. If true, the rejected prow of the barge at the extreme left may never have been fully obliterated.?

From the moment an artist completes an oil painting, the painting begins to change color. The shift is gradual, taking decades, or even centuries, but eventually colors fade, darken, or become more transparent over time. Oil paint is made of pigment particles suspended in an oil binder. The variety of substances used as pigment make some colors susceptible to aging.

For example, mineral-based pigments such as verdigris, a green color made from copper, changes to a dark brown over time. This pigment, which was widely used in the 15th century, left many great works much darker than intended.

In contrast, pigments produced from organic dyes, such as rose madder and indigo, are susceptible to fading when exposed to light. The loss of color from a yellow gamboges glaze, based on plant resins, can make green foliage in Dutch flower paintings appear blue.

Environmental contaminants can also be damaging to colors. For example, hydrogen sulfide in the air converts white colored, lead based paint to black colored lead sulfide.

As if that weren?t enough to keep restoration experts busy, natural resin varnishes meant to protect paintings, turn yellow with age as well. This makes an artist?s white highlights seem stained, causes blues to appear green, and reds to appear orange.

Proper storage, out of direct sunlight, and with controlled temperature and humidity, is the only thing that can slow the aging process. Preservation is important because shifts in color and opacity change the way we perceive paintings. Illusions of depth and three-dimensional form depend on subtle transitions in color and tone that are often obscured, and sometimes lost as a painting ages.

Date: 2016-06-12; view: 122