[Pigments and Binders]

Gamboge

History of Use by Artists

The earliest evidence of the use of Gamboge comes from eighth century East Asia. It is onlypresumed that the organic yellow colorant found on artifacts from this period is gamboge. Gamboge was used as a watercolor pigment in the countries of Eastern Asia from its origin in the eighth century A.D. Evidence of yellow ink made from gamboge exists on black (khoi) paper in Thailand and a 12th century scroll depiction of The Tale of The Genji. After is arrival in Europe in the seventeenth century, gamboge found other applications. The pigment was used as a transparent oil color by Flemish painters, but additives such as resin or wax were necessary to enhance its permanence and durability. The pigment was also made more usable by mixing it with other yellow pigments such as lemon yellow or alumnia. (Fitzhugh)

This pigment can be found in places like one of Rembrandt's paintings in the Staatliche Kuntstsammlungen in Dresden. Fragments of gamboge were also found in the paintboxes of John Mallord William Turner and Townsend. An interesting discovery of gamboge was found on an Armenian gospel done about 1300. If this identification is confirmed, it would prove gamboge's presence is Asia Minor in that time. (Fitzhugh)

Many sources refer to gamboge being used to make a transparent yellow varnish for the coloring of wood, metals, and leather. In the nineteenth century, gamboge was a common ingredient of varnishes, especially metal varnishes used ot color scientific instruments. (Fitzhugh)

Source/Preparation of Pigment

Gamboge is most commonly extracted by tapping from the tree Garcinia hanburyi.. The trees must be ten years old before they are taped. The resin is extracted by making spiral incisions in the bark and by breaking off the leaves and shoots of the tree and letting the milky yellow resinous gum drip out. The resulting latex that exudes out is collected in hollow bamboo. When the latex is congealed, the bamboo is broken away and large rods of raw gamboge remain. (Fitzhugh)

Raw gamboge is usually in the form of hard, brittle lumps of a dull, dark yellow color, which when pulverized, turns into a bright yellow powder. This powder is ground or mixed with a variety of binders in order to make paints and varnishes. In order to effectively use gamboge as a paint pigment, additives must be used to improve its permanence and durability. Gamobge pigment is also used with other pigments in order to intensify their colors, while giving gamboge some of the essential characteristics it lacks. This only works well with a few select pigments. When mixed with most high-chroma pigments, the gamboge eventually disappears and what was once a beautiful green or orange turns back into blue or red. Economically, other pigments are more sensible to use, so the use of gamboge has drastically declined in the twentieth century. In fact, modern-day pigment experts recommend that the only admissible use for gamboge is in leaf-gilding on paper or parchment by precoating the support, then breathing on the paper to make it tacky. (Fitzhugh)


Chemistry of the Pigment

Gamboge usually contains about 70% to 80% yellow resin, and 15% to 25% water-soluble gum. the remaining portion is composed of esters, hydrocarbons, wax, ash residue, and vegetable detritus. Most investigation of commercial gamboge products have found that the major constituent of the resin is gambogic acid.
R₁=(CH₂)₂C=CH(CH₂)₂,R ₂=CO₂H,R₃=CH₃
There has been less investigation of the gum component of the pigment, but it is hydrocarbon based. (Fitzhugh)


Gamboge's transparency hinders its identification in many ancient works of art. This transparency can be a drawback with reflectance spectroscopy since the spectrum obtained is likely to be a combination of the spectra for the medium, the underlying pigments, and the support material, as well as the gamboge pigment. ( Fitzhugh)

The most successful method of identification for the presence of gamboge is ultraviolet-visible absorption spectroscopy. By using this method, one can single out gamboge for its high absorption of the ultraviolet spectrum, as well as its characteristic spectrum, as other pigments similar in color do not have as high an absorption rate. Another interesting yet less accurate method of identifying gamboge is called chromatography. Gamboge-resin has an Rf value of about 0.64. This measure of migration on the plate is fairly distinctive to gamboge-resin. The resultant identification can be double-checked through the implementation of either fluorescent plates, which contain a phosphorous material that is illuminated under fluorescent light, or by spraying the orginal plates with a fluorescent dye such as rhodamine B. Under ultraviolet radiation, dark spots can be seen where the gamboge resin has absorbed the ultraviolet spectra. (Fitzhugh)

Binders

Historically, it is not clear how often gamboge used as a watercolor paint was mixed with any of the usual media, but it apears such compunding was not necessary and may have been minimal. Gamboge mixes well with watercolor binders, such as gum arabic. As seen in our laboratory experiments, this mixture produces a consistent, deep color and a quality texture. When gamboge was used as a oilcolor, however, it was necesary to add either resin or wax to it to ensure its durability and to prevent "striking through" (Fitzhugh, 149). Where gamboge has been made up in an oil medium, it has the properties of a glaze (Fitzhugh, 145).


Pictured above is our lab setup. Samples A B and C correspond in order with the below information. The mortar contains gamboge pigment mixed with linseed oil. The top glass plate shows gamobge mixed with various other lab made paints.

 

	Transparency/Opacity	Color/Mixture Uniformity	Color Retention After Drying
Gum Arabic	most opaque	Color: Very smooth and uniform  Mixture: Also smooth and uniform	Good color retention
Linseed Oil	least opaque	Color: inconsistent and grainy  Mixture: grainy and clumpy	Color changes to a dull brown
Egg Tempra	Inbetween	Color: Smooth and uniform  Mixture: Smooth, but required constant grinding in order to keep from drying out	Color changed to a slightly darker yellow

 

Optical characteristics: Looking through the microscope

When Gamboge is observed through a microscope, it's most evident characterisitc if its inconsistency. What looks pretty much yellow-orange to the naked eye becomes a virtual rainbow of color when intensified under a microscope. We observed gamboge pigment alone, and mixtures of gamboge with linseed oil, gum arabic, and egg yolk tempera.

Gamboge Pigment- Pigment present in varying irregular shapes. The size of these shapes ranges from 1.25 nm to 7.5 nm. The grains are rather opaque and range in color from greenish yellow on the edges of the grains to orangeish yellow on the inside. The picture to the right is gamboge pigment grains at 20X their actual size.

Gamboge and Linseed Oil- Pigment/binder mixture is present in varying irregular shapes. Only about 4/5 of the mixture forms a deep yellow. The other about 20% is a light butter yellow, and surrounds the particles of deeper yellow color. Occasional bright orange and reddish-maroon spots are also present, which may be spots of very highly concentrated pigment.

Gamboge and Gum Arabic- The shape of these particles is hard to identify because the pigment and binder almost completely mix. Although the substance is obviously porous, it is a relatively consistent orange, only a few lighter spots show through. Opacity is low, and light from the microscope shone through easily.

 
Gamboge and Egg Yolk Tempera- This mixture yielded a highly irregular amoebic-shaped pattern of particles. It looked as if cracks were present, and these cracks in the pigment/binder mixture allowed light to shine through. Around the edges, the color is much darker, but in the middle, the egg tempera mixture is a strange greenish-yellow, not like the other two mixtures which were predominantly and orange-yellow.

Health Issues

Besides its use as a colorant, gamboge was frequently prescribed as a cathartic or purgative, a powerful laxative used to cleanse the bowels (connerprairie.com)-www.connerprairie.org/cp/jmed.html. It was also used to lower blood pressure and as an intensifier for other purgatives. Medicinal usage of gamboge lost popularity quickly due to its side affects and toxicity. The powder was known to induce vomitimg, nausea and griping. A dose of one drachm (3.5516 ml) has been known to cause death. The safe doses (from 2 to 6 grains) were very difficult to measure out, so use as medicine was abandoned except in treating tapeworms (botanical.com)-www.botanical/mgmh/g/gobog05.html#des.

Links to other Web sites

CONNER PRAIRIE (www.connerprairie.org/cp/jmed.html) a treatise on early medicine
BOTANICAL.COM (www.botanical/mgmh/g/gobog05.html#des)- a guide to gamboge and other herbal medicines
GAMBLIN COLORS.COM (www.gamblincolors.com/yellow.html) a paint company's rendition of the history of yellow pigments

Other

Gamboge from Garcinia trees is often confused with another yellow pigment, Indian Yellow. In his presentation to our class, Nigel McGilchrist referred to Indian Yellow as Gamboge, but there is a difference. The other pigment is derived in a very unique way. Indian yellow producers force fed cows mango leaves and gave them no water. Their urine was collected in dirt balls and sold as "pigment" (gamblincolors.com). This method of collecting pigment was lost in the rise of manufactured synthetic pigments.

ANOTHER INTERESTING GAMBOGE TIDBIT!!!!!

In 1910, uniform colloidal gamboge particles were used to study Brownian motion. This same experiment with gamboge helped scientists attain a value for Avogadro's number. (Fitzhugh, 145)

Patrick Craig and Lora Napier, 1998.

Sources:

Fitzhugh, Elisabeth. Artist's Pigments : a handbook of their history and characteristics , 1986.

http://www.connerprairie.org

http://www.botanical.com

http://www.gamblincolors.com