HISTORICAL MATERIALS/TECHNIQUES

RESINS AND VARNISHES

Contents

What are Resins?

Natural resins are organic solvent soluble plant exudes. The exception is shellac which comes is created by the lac incest and is soluble in ethanol. Resins have been used as paint additives, binders, and especially, as transparent varnish coatings (The Organic Chemistry of Museum Objects).

Examples of Resins and Varnishes:

Amber – Amber is a fossilized resin that originates from prehistoric conifer trees and comes in a wide range of colors, from a pale yellow to an opaque red-brown. Amber can be found in several deposits worldwide, but amber resin obtained near the Baltic region is recognized by many to be “true” amber. This is due to Baltic amber’s higher level of succinic acid, which is often used to characterize a higher quality resin (although some judge quality based on its color). Amber has been used since ancient times as a principal component in varnishes, but due to its extremely high melting point (< 300º C) and high cost the resin is now mostly used for decorative purposes (i.e. jewelry).

Batu East India Bold – “Batu” resin represents one of the many forms of dammar resin that can be found throughout India and East Asia. “Batu” and “black dammar” are terms that are commonly used to describe the wide range of resins originating from these areas. Dammars that are higher in opacity are often considered to be less superior in quality but continue to be used in the varnish trade. This particular grade is a fossilized form of dammar that was most likely obtained from the ground near Borneo and is soluble in aromatic and turpentine solvents.

Black East India Bold – Like Batu dammar, this dark colored fossilized resin obtained near Borneo is related to the Dammars.  With a greater degree of transparency, Black East India resins have been used in paints, varnishes, and printing inks. Soluble in aromatic and turpentine solvents, the resin will produce a varnish that will become much lighter over time as it is subjected to light.

Burgundy – Collected from the Picea Abies (pine family) in Europe, this resin has been used as a varnish for wooden objects, especially musical instruments.

Dammar –  Dammar consists of triterpenoid resins collected from trees belonging to the Dipterocarpaceae family. Like Mastic, dammar has been used as a varnish but tends to yellow and degrade with age. Soluble in a variety of petroleum based solvents, dammar has been used as a varnish since the early 19th century.

Dragonsblood – Now collected from various parts of Asia, this resin was originally harvested from the Dracaena cinnabari tree off the coast of Eastern Africa as well as the Canary Islands. Like gum acoroides this red-colored resin has been used as an additive to varnishes dissolved in alcohol (also used on instruments).  Dragonsblood has also been used as a stop varnish for etching zinc with nitric acid.

Gamboge –  The main supply of this yellow resin is from Thailand where the trees are tapped and the resin collected in hollow bamboos. Like resina kamala, this alcohol soluble powder is extremely toxic and is used to color spirit varnishes (often as a ground color for violins).

Gum Acoroides (Yacca) – This colorant is obtained from yacca gum that is harvested from Xanthorrhoea plants native to Australia.  While yacca is mostly used in the production of fireworks, the resin produces a beautiful red hue when dissolved in alcohol and is added to varnishes and coatings to impart color, especially for wooden instruments).

Light/Dark Colophony– Colophony is often referred to as rosin in industry and is obtained from various types of pines and conifers.  Once the resin has been collected from the tree, the oil of turpentine is distilled from the resinous exudates and the rosin is left behind. The color of the resin is directly related to the manner in which this distillation process is performed. Colophony has a wide range of use in the arts including paper sizing, printing inks, soldering fluxes, and as an additive in painting. It is soluble in turpentine solvents.

Mastic – This triterpenoid resin, obtained throughout Europe, India, Turkey, and South Africa, is one of the oldest resins used in the history of art. Harvested from the pistachio tree (Pistacia Lentiscus), Mastic is commonly used as a varnish and paint additive and is soluble in turpentine solvents. Unfortunately this natural resin has a tendency to yellow and degrade over time.

Resina Kamala – This fine powdered resin is collected from the hairs of the fruit collected from a lotus tree found in the Philippines, Asia, and the Middle East. This highly toxic colorant is valued for its intense yellow color and is often used as an additive to varnishes.

Sandarac – This natural resin is harvested from the Tetraclinis articulata tree (cypress) that is indigenous to North Africa and Southern Morocco. Like Mastic, Sandarac has been used as a varnish since ancient times. It is soluble in more polar solvents like acetone and alcohol, making it a popular material for spirit varnishes.

Oil Resin Varnishes – Ancient recipes dating back to the Middle Ages have detailed recipes for oil resin varnishes, materials that were generally used as surface coatings. The resins must be heated in hot oil or heated until liquid and then mixed with hot oil. Extremely high temperatures are needed to create these semi-transparent varnishes and conservation researcher Brian Baade has been able to produce at least four different varieties (Congo Copal, Amber, Manila Copal, and Sandarac). ​

Works Cited

Mills, John S., Raymond White, “Carbohydrates: Sugars and Polysaccharides” in Organic Chemistry of Museum Objects, Reed Educational and Professional Publishing (1994): 76.