Madonna in a Church
|On this page I will outline finishes available, their proper use and/or compatibilities, as well as their archive expectations to protect art from the elements and ultraviolet light.Finishes, depending on the desired effect, can be applied with a brush, roller, or spray. They could consist as a fixative to utilize as a sealing top coat or between layers to prevent shifting or smudges. Also available as a Removable Varnish , some finishes are designed to be removed easily to retouch. Others are completely permanent and almost all of them are supplied in a matte, satin or gloss luster.
In most cases application guidelines apply with requirements for each specific medium. One of the obvious, with the exception of some urethanes, is not to apply water based finishes over oil based paint.
Considerations should be taken to be certain the finish you are applying meets your requirements for today and the future. Making the right decision will assure your painting’s preservation.
With all mediums be absolutely positive you have allowed adequate curing/drying time for the paint before applying your finish. Applying a sealing finish too soon has been associated as a cause of surface cracking.
- Waxes and Oil Varnishes – many variations of oil and wax finishes have been used for furniture and paintings for centuries. These finishes usually consist of purified beeswax and/or carnauba wax that has been diluted with mineral spirits and are blended with a varnish resin such as damar or copal. A common wax-resin formula is to blend one part beeswax with one and a half parts mineral spirits and one part oil-resin varnish. Application is usually brushed or rubbed on applied in small sections of the painting at a time and buffed with a cotton flannel cloth before moving on to the next area. A plus is that most wax finishes retain flexibility and protective qualities for lengthy periods of time only require dusting or polishing with a dry cotton cloth and can be dissolved to remove for refinishing with mineral spirits used lightly without damaging the art.
- Oleoresin Varnishes – resins are considered permanent and were used in conjunction with oils to harden the surface, increase depth and provide a stronger shield. The term varnish (developed by renaissance Flemish artists) mentioned in old notes taken by Cennini as ” Vernice Liquida,” was the current finishing coating during the period to protect tempera and oil paintings. It is produced from sandarac resin, which comes from a tree similar to the juniper found in Morocco and some areas of the East, blended with linseed or walnut oil and applied with a sponge or brush. Because this varnish also became rather deeply red in color when processed old master’s paintings were completed with a green tint so that once they were finished with varnish the color would be neutralized. Other resins were frequently used such as Amber, Copal and Damar. Although Amber was most popular with the Flemish artists, it has been known to yellow with age. Copal resins have proven to be the most archival resin used in an oil finish where as it dries harder, is most durable and any yellowing can be cleared by exposing it to sunlight. Because Copal resin accelerates paint film dry time, it has been proven to be best used when incorporated into oil mediums to increase durability, transparency and luster to the paint film negating the need for a finish.Due to it’s reasonable cost verses durability Damar Gum has become the most popular of clear varnishes since the 20th century to use with oils. Because damar is not completely soluble in mineral spirits, only pure gum turpentine should be used. It should also be noted that damar is a soft resin that is prone to dry out and crack with age but is easily removed to restore the finish.
- Lacquer – is a thousand year old finish developed in the East and is applied in numerous quick drying thin coats to built a deep rich luster. Lacquer is a clear sap taken from any of six species of trees growing in the East and harvested like rubber, by cutting the truck and letting the sap flow. Special ventilation provisions must be taken to use this paint and/or finish. Lacquer itself has been “noted as a skin irritant, and potentially carcinogenic“. Although Lacquer will liquefy in denatured alcohol, generally it’s in a solvent mixture of acetone, naphtha, xylene, toluene, and ketones. Because of the hazards associated with the solvents used, lacquers target market in the USA are exclusively to industrial and furniture applications. I have more information about lacquers in the copper and air brush pages.
- Shellac – is a product similar to lacquer except it consists of a resin from secretions of the insect, it’s alcohol based, usually blends of ethanol and methanol, and it was created for it’s adhesion properties. This is why sometimes Shellac Varnishes are also blended with pigment to use as a primer, or applied between layers to improve the strength of the paint. Because shellac usually turns dark and cracks with age it is not usually associated for use with picture finishing other than when thinned and applied as a spray fixative/finish for dry media drawings. Shellac can be removed with denatured alcohol.
- Acrylic Varnishes – are best used to produce a uniform luster over acrylic paintings or pencil or watercolor as well as seal and protect the painting. Rubbing a rag dampened with denatured alcohol on the painting will remove the finish but it should be done carefully to avoid also removing parts of the painting. Acrylic Varnishes have received greatest recognition because they can be easily removed if the picture needs to be cleaned or restored. Regardless of claims, I would never use these over any oil base painting.
- Urethanes – originally produced as an oil base finish for floors is also now produced as a water soluble finish in a matte or high gloss luster. Paint or varnish remover will soften to remove urethanes, but you’ll still have to scrape and sand some of the finish off. Because of Urethane’s permanence where it’s removal will most likely destroy your painting, it would be wise to be certain about it’s application before using .