The word "varnish" has only been used to describe a transparent coating on paintings for a comparatively short time - it has undergone several shifts in meaning over the centuries.
What is varnish? Since when has it been used?
The name "varnish" is derived from the French word "vernis" for "varnish" and today refers to the transparent, protective intermediate or final layer on many paintings and artifacts. Depending on the technique and area of application, the ingredients vary slightly - there are varnishes based on linseed oil, turpentine oil, resin or alcohol.
The origin of the word "vernis" probably comes from the place name "Berenike, a town in what is now Libya, from which sandarak, the first resin processed into varnish, was imported in ancient times. In the centuries that followed, the word long referred to all paints that, pigmented or transparent, formed a hard, glossy coating, usually by containing resins. As late as the 18th century, water-based coatings were also included, for example with gum arabic or hide glue, with which, for example, charcoal or pastel drawings were fixed.
It was not until the 19th century that a shift in meaning took place in German in the direction of a clear protective coating, especially on works of art, probably due to the increased use of shellac, which served as a coating for furniture, but also on paintings. The word "vernissage" is also related to this - the date when the final varnish on many of the paintings on display was still fresh.
Components and properties
On traditional oil paintings, the varnish usually consists of linseed oil mixed with dissolved dammar or mastic resin. Shellac was sometimes used to fix charcoal or pastel drawings. Other types include resins dissolved in turpentine oil (for example, dammar) or waxes (such as beeswax) - dammar gives paintings high color brilliance, depth, and strong gloss, while beeswax gives them a silky matte finish. Depending on the requirements, both can be mixed together in different proportions.
Today there are also varnishes made of synthetic resins, which sometimes have better properties - even higher transparency, hardness and resistance to variations in temperature and humidity. However, their properties over a long period of time cannot be assessed at present, which is why they are used in restoration with extreme caution and only rarely.
As an intermediate varnish, varnish counteracts the frequent problem that the primer layers absorb all the binding agents of the middle layers and thus distort their appearance - varnish can compensate for this effect and restore color brilliance. As a finishing varnish, it gives depth to the colors and a strong gloss to the painting surface; the surface becomes water and dirt repellent to a certain degree. It was also once believed to help prevent craquelure, but this assumption has since been disproved.
Shellac on wooden furniture
Shellac is a transparent, colorless-yellowish to red resin that, dissolved in alcohol, can be applied to smooth wooden surfaces as a protective coating. It colors the wood slightly, adds visual depth to the grain, and makes the surface water repellent so it can be wiped clean with a damp cloth. It was especially popular in the Baroque and Biedermeier periods, when particularly beautifully grained woods such as walnut, root woods and the like were often used - a coat of shellac brought out the grain even more.
Monument protection and restoration
In building and monument conservation, the word "varnish" refers to a protective coating of boiled linseed oil or linseed oil-based varnish, for example on wooden beams on half-timbered houses, shutters and doors - this coating is not necessarily transparent, however, but can be colored or pigmented.
In the field of restoration, it often plays a role that varnish darkens considerably over the years and affects the appearance of old paintings. Therefore, the first step in a painting restoration is often to dissolve and remove old varnish using a cotton swab soaked in alcohol (isopropanol or ethanol). After restoration, a new final varnish is then applied.