An unvarnished painting is vulnerable to dirt and dust that will eventually become embedded in the paint. It is also subject to deterioration caused by ultraviolet light and oxidation, and abrasion from handling and transport. A varnish can protect the painting from dirt, ultraviolet light and abrasion. Applying a varnish to your painting than is an important part of maintaining its appearance and value. If you decide to apply a varnish to your painting, you must decide on the type of varnish, method of application, and desired final appearance. The following discussion can help you make the right choice for your art work.

The word resin when used in its most specific sense is a hydrocarbon secretion of many plants, particularly coniferous trees. The resin produced by these plants is a viscous liquid, composed mainly of volatile terpenes. Oleoresins are naturally occurring mixtures of oil and resin. Other resinous products in their natural condition are a mixture of gum or mucilaginous substances and are known as "gum resins." Mastic gum is a good example of a gum resin.

The meaning of terms used in fine art painting.

Shellac is a resin secreted by the female lac bug, Kerria lacca (Order Hemiptera, Family Coccidae) on trees in the forests of India and Thailand. The insect secretes resin forming tunnel-like tubes as it traverses the branches of trees. This insect is in the same family as the insect from which cochineal is obtained. The resin is collected, processed and sold as dry flakes that can be dissolved in ethyl alcohol to make liquid shellac. Shellac forms a durable natural coating that is useful as a primer, sanding sealant, tannin-blocker, odor-blocker and high-gloss varnish.

Dammar (or damar) or soft copal varnishes are soft, very flexible and transparent, but dry slowly. These varnishes have a bright appearance and a faint pale yellow color. The color may be varied from golden yellow to yellowish brown by gamboge, dragon's blood and asphaltum.

A varnish is a transparent, hard, protective film primarily used to provide a protective layer over artwork. Varnishes are traditionally a combination of drying oil, resin and solvent. Varnish finishes are usually glossy but may be made to produce satin or matte surface by the addition of "flatting" agents. Varnish has little or no color, is transparent, and has no added pigment, as opposed to paint or stain, which contains pigments or dyes and generally range from opaque to translucent. Varnishes are also applied between layers of paint to isolate them or over substrates, such as wood, to seal them and reduce absorbency.

Formulas for varnishes and mediums call for measurements that are often confusing for artists. For example, in his formula for a glazing medium, Ralph Mayer calls for a “5-pound cut” of dammar (or damar) varnish. This measurement refers to the amount of dry dammar resin with spirits of gum turpentine in a ratio called a “cut,” which refers to the amount of resin in pounds dissolved in a gallon of turpentine. This measurement is simple enough to use when preparing your own varnish, but what if you want to use a commercially-prepared dammar varnish, such as Rublev Colours Dammar Varnish or Neil’s Best Dammar Varnish? How do you know if it is a 5-pound cut?

Congo copal is no longer available commercially (at least as it was available in commerce formerly), because the suppliers have long stopped trading due to strife in Africa since the last quarter of the 20th century. Trade of Congo copal was once controlled by the Belgian government, but as this region of Africa gained independence, and the demand for copal resins diminished during the last half of the 20th century, commerce of Congo copal has all but ceased.