While responses to this thread contain a lot of good information, there are also a number of errors, misconceptions and suggestions which are not entirely sound if taken as unqualified advice.
At the risk of starting a flame war, I presume to address them on the basis of 50 years experience painting in oils, and dealing with a wide variety of paint materials of all types:
Quote:
|
Originally Posted by Claudemir Bonfim
. . . oil paint never dries, it solidifies with the addition of oxygen molecules, and that's why the paint yellows with time. If the painting is varnished, then . . . the varnish yellows first . . .
Avoid organic varnishes!
. . . Paintings in museums receive very thick coats of varnish . .
|
One problem in discussing materials and methods is first to define the terms. Most people understand paint to be "dry" when it can no longer be manipulated, lifted from the surface, or malleable when handled. Claudemir is correct to state that the process of oxidation continues in oil paint films for a long time. However, for the purpose of addressing the question of a "final varnish" for a painting, it is only necessary for a paint film to reach a state where free volatiles have evaporated. As further noted, the length of time for a painting to reach this condition depends upon the thickness of the films and also ambient conditions.
The ultimate yellowing of oil films is a chemical reaction which has nothing to do with the oxidation of polymerized oils and/or resins. Curiously, the nature of linseed oil paint films is to yellow and darken when deprived of ambient sunlight. Humidity exacerbates the yellowing process, which is readily demonstrated by the oil itself, even before being incorporated into paint; it becomes increasingly lighter when exposed to sunlight.
A painting stored in a dark, damp place may yellow very noticeably in a relatively short time. Exposed to normal room (sun)light, the yellowing will reverse. The oil films cease to be reversibly reactive when the paint film has reached a certain point in the aging process . . . usually several decades.
Yellowing of the varnish films is a process independent of reactions taking place within the painting. Many old paintings have been restored to a state nearing their original condition when multiple layers of varnishes applied through the centuries (and the dirt, dust and smoke they contained) were removed by conservators. The most famous example was when Rembrandt's painting
"The Night Watch" was restored. It had been referred to by that popular name for a great many years, when in fact, it is a daylight scene. (proper title,
"The Company of Frans Banning Cocq and Willem Van Ruytenburch )
All solvents, vehicles, oils and resins generally associated with oil painting are "organic" in the sense of the definition of "organic chemistry".
Modern conservation methods find the old practice of applying numerous heavy coatings of varnishes of various compositions anathema to preservation.
While the wikipedia link provided is a good general-knowledge overview of materials which the term "varnish" comprises, it has little or no practical application to the especiality of oil painting or the preservation of oil paintings. For that matter, linseed oil alone is, by definition, a varnish in itself!
Quote:
|
Originally Posted by Marcus Lim
. . . actual fact is the painting is still 'growing' inside the painting . . . varnish too early results in serious cracking problems . . . think Bruce Banner ripping his clothes off when turning into a hulk . . .
|
Marcus, the principle is correct, but you have it reversed. As paint films continue to dry and give up their volatiles, they
shrink They do NOT "grow". Problems with cracking and crazing may be caused by violating the "fat over lean" principle when making the painting. If thin, faster drying (lean) layers are applied over heavier, slow-drying (fat) layers, the lean layer will shrink or embrittle over a soft layer which is not shrinking. Think of Bruce Banner watching the surface of a mud-hole crack in a net-pattern as it bakes in the sun!
Varnishing too soon may cause cracking, but a more likely result (for damar or mastic at least) will be that the varnish will become incorporated into the painting itself through the process of solvent transfer, negating the advisability of having a "final varnish" be a removable, protective layer.
Quote:
|
Originally Posted by Michael Georges
. . . I have varnished paintings that were more than 25 years old . . . used . . . good turpentine to wipe the whole painting down . . . I add a bit of wax medium to my varnish . . . more of a satin finish.
|
While a painting 25 years old could very likely suffer a wiping with turps (or any other solvent) without visible damage, most conservators would cringe at the thought. Usually, the first line of cleaning is to dab the painting surface with surgical cotton dampened in distilled water. Of course, extreme cases would require something more, but in general, it's not a good idea to wipe down any painting with solvents prior to varnishing.
Adding wax to a "final varnish" is questionable on a number of levels. First would be the question whether the varnish chosen and wax are compatible. Damar and pure beeswax is a compatible mixture. The problem is the result is a varnish that is malleable, attracts dirt in its own right, and is much softer than damar alone.
In choosing a material to use as a final varnish, two requirements are inviolable: 1. The varnish should provide protection 2. The varnish should remain indefinitely soluble in its parent solvent to enable its ready removal at a future date.
A better long-range tactic would be to apply a suitable material as a final varnish, and regardless of its composition or final glossiness, a satin finish may be readily achieved by the application of a wax layer
that is not part of the varnish
Quote:
|
Originally Posted by Claudemir Bonfim
Some guys like Damar, I personally think that it yellows too fast, but other[s] . . . haven't experienced the same problem, I think tht's due to climate differences . . .
|
Here, Claudemir addresses a major problem we encounter in discussing materials and methods. The traditional materials of oil painting have always been open to the question of the nature of the source, and the quality of the material. Resins are especially problematic, as those commonly associated with oil painting (damar, copal, mastic); each is a generic term encompassing a wide range of similar species, each with quite different individual qualities and properties. Sometimes it depends where certain species are grown.
What works well for me in the dry, cool climate of the high desert US west may very well cause specific problems in the humidity of tropical Brazil ! This is why it is so necessary for painters to become intimately acquainted with their materials, and knowledgeable by running their own tests. It's fascinating how closely processes in the studio and the kitchen are related! About the relative quality of materials, I could never understand how anyone could dislike oysters . . . until I was served a "bad" one! Simlar considerations apply to the painting materials we prefer!
Quote:
|
Originally Posted by Jennifer Bogartz
. . . Why is it best to avoid organic varnishes like the one made out of egg white and salt?
|
Our modern "just run down to the store" culture primes us to be surprised at such a suggestion as using egg-white for varnish. Anyone who has left the dirty dishes in the sink overnight quickly realizes that a number of food-stuffs are very tenacious adhesives and coatings . . . In earlier times, folks were intimately acquainted with where their lunch came from, and readily observed how blood, milk, eggs, and a number of other "food" items could provide substance for "paints" of different types and applications.
If you have ever encountered the "beauty secret" of using egg-whites in a facial treatment (to eliminate wrinkles?) you can readily understand how using egg-white "varnish" on a painting might not be the best choice . . . shrinkage is extreme, the film is brittle, and although Claudemir refers to being able to remove it easily with water, I wonder . . . after all, eggs (the yolk) are the major ingredient in "egg tempera" . . . a paint choice that's far more stable and permanent than oils! (ever had your car "egged" ??)
Linear Mode
