Asphaltum and bitumen are broad terms for a wide range of substances based on high-molecular hydrocarbons. From the viewpoint of current art historical research, bitumen represents a large group of organic substances, which consist of an indefinable mixture of high-molecular hydrocarbons. Bitumen either occurs naturally or is obtained from the synthetic distillation of petroleum. Depending upon its place of origin or technique of manufacturing, bitumen possesses a composition of different characteristics.
The English term "bitumen" is used to designate a wide variety of hydrocarbon substances, just as pitch is a term used to designate bituminous substances based on petroleum (such as "glance pitch") and substances from the sap of trees (such as "Burgundy pitch"). However, the term as used in painting usually designated a substance based on hydrocarbons derived from petroleum (at least after the 16th century).
Asphaltum typically designates a species of bitumen, including dark colored, comparatively hard and non-volatile solids; composed of hydrocarbons, substantially free from oxygenated bodies and crystallizable paraffin; sometimes associated with mineral matter, the non-mineral constituents being difficultly fusible and largely soluble in carbon disulfide; the distillation residue yields considerable sulfonation residue. This definition includes Gilsonite and glance pitch.
In his essay about manuscript painting from the year 1988, Heinz Roosen-Runge mentions a recipe from a German manuscript of the late fifteenth century, in which bitumen is used to describe an aqueous binding agent for manuscript painting, made of a mixture of fish glue and rabbit skin glue. Apparently, this was a typical name for such a binding agent mixture, because it is found in another passage in the Neapeler Codex from the fourteenth century and by Valentin Boltz writing on the same subject in Illuminierbuch (1549). In another example, Zahira Veliz identifies this term in a collection of Spanish and Portuguese treatises of the sixteenth and seventeenth centuries: from a Portuguese manuscript of 1615, the use of bitumen is specified in a varnish for marquetry, which was part of a recipe to make a red lacquer with the pigment and rosin.
It was at one time believed that bitumen was used in the bandages of mummies, but this was generally not the case (instead, balsams were used). Perhaps this error resulted in some confusion, which may have lead individuals to grind actual mummies for use as a pigment, perhaps as an alternative to asphaltum. Of course, the origin of the English word "mummy" is from the Persian or Arabic word, "mumia" or "mumiya,” meaning asphaltum or bitumen, which may have caused some confusion about the real source of this pigment.
For further reading on this subject, I recommend the article by Sally Woodcock (1996), "Body Colour: the Misuse of Mummy," The Conservator, 20.
As an aside, Natural Pigments is trying to obtain Dead Sea or Palestinian bitumen. We have contacted some Jordanian mineral exporters, so we will see what they say in due time. According to sources, Dead Sea bitumen contains less soft hydrocarbons then typical sources for of bitumen, such as from Trinidad. However, our findings show that Gilsonite, or North American Asphaltum, which is a natural, resinous hydrocarbon found in the Uintah Basin in northeastern Utah, is a very hard substance. This natural asphalt is similar to hard petroleum asphalt and is often called asphaltite, uintaite or asphaltum.
By the way, Natural Pigments offers a pigment, known as "mummy" in Russian, and so we have kept the use of the name, although it is not from real ground mummies. The text on the Natural Pigments Web site states:
The confusion in ancient times was very great, so that the Persians and Arabians used the word "mumiya" to designate bitumen, because they believed it was the same substance used by the Egyptians in the wrappings of mummies.Mummy brown is a deep brown color, nearly intermediate in tint between burnt umber and raw umber. A pigment of this color was also prepared from bitumen or asphaltum. In Russia, the term "mummy" has been applied to mineral pigments that exhibited similar characteristics to this pigment. Since we derive our pigment from Russia, we have maintained the use of its name.
We know something about how the Old Masters used asphaltum in their paintings, because we have recipes and references to the use of this pigment. Most likely, there were not one but many different methods in which the Old Masters used this pigment, because there were different forms of it available throughout the medieval and Renaissance period. For example, in describing the different forms of bitumen used during this period, Roosen-Runge wrote, "One form is bitumen that is equivalent to the modern definition of bitumen, another is bitumen that is a 'new, as it were, improved bitumen, which dries harder than the usual bitumen', and a third is the color collected from mummies." (Roosen-Runge, 1967)
Historically, there were two basic methods of preparing asphaltum in oil. One method was to melt the asphaltum in turpentine and then mix this liquid with oil, beeswax and Venice turpentine. Another method was to burn the asphaltum to a cinder (thereby removing most of the easily volatile matter), crush it to a fine powder and then grind it with a drying oil, typically boiled linseed oil.
Mérimée described the two basic methods for the use of asphaltum in painting, the first one he attributed to the Italians and the English. This method, which involved dissolving asphaltum in a solvent, such as turpentine, prior to adding it to oil, would result in paint that lacked body, so many recipes call for the addition of resin or balsam, such as mastic or Venice turpentine, or wax or both types of substances. The second method, which involved calcining asphaltum to eliminate easily volatilized substances and then grinding it with drying oil, would have body and is more readily usable as such. Our theory is that the latter form that is more durable in oil painting.
Mérimée provides a recipe for the Italian and English method that includes asphaltum, gum lac, linseed oil and wax:
Natural Pigments (January 25, 2007) offers powdered asphaltum based on Gilsonite, a natural bitumen, which is a harder, less volatile form of bitumen. While it is still soluble in turpentine and mineral spirits, it is much harder than synthetic bitumen."The gum lac is first dissolved in the turpentine by adding fifteen grains at a time, and allow it to melt before the other portion is added; the asphaltum is then to be mixed in like manner, by degrees; the linseed oil, having been heated near to the boiling point, is also by degrees mingled with the rest; the wax is then added. Before the mixture cools, it should be thrown upon the stone, and well worked with the muller and knife." (Mérimée, 1839, p. 182)
Although asphaltum has a bad reputation in art history for ruining works of art, there are examples of its use where this is not the case. It may not be so terrible in oil painting, especially with the second method of preparation. Natural Pigments will offer Asphaltum as part of Rublev Colours Artists Oils.
Although many aspersions have been cast upon the use of any asphaltum in oil painting, it is interesting to note these comments by Church:
Church had distinguished between the source of asphaltum earlier in his 1890 edition by endorsing the use of native asphaltum when properly prepared:"The disadvantages attending to the use of these coal-tar browns and of ordinary asphalt are two-fold. Not only are they treacherous on account of their easy fusibility, but they are liable to stain contiguous pigments by reason of their solubility in oil or varnish. When used successfully by the older artists they were always introduced sparingly, or were largely commingled with more solid paints." (1901, op. 236)
Personally, I think asphaltum in oil painting should be revisited, but in carefully controlled and limited circumstances to determine if it can be employed safely used in modern art works."The operation of roasting native asphalt -- keeping it over a slow fire 'till it will boil no more and becomes nearly a cinder' – was recommended by Williams in his 'Essay on the Mechanic of Oil-Colours' (1787), and furnishes a perfectly satisfactory and safe product." (1890, p. 208)
Church, A. H. (1890). The Chemistry of Paints and Painting. London: Seeley, Service & Co., Ltd.
Church, A. H. (1901). The Chemistry of Paints and Painting. London: Seeley, Service & Co., Ltd.
Mérimée, J. F. L. (1839). The art of painting in oil, and in fresco; Being a history of the various processes and materials employed, from its discovery, by Hubert and John van Eyck, to the present time. Trans., W. B. Sarsfield Taylor. London: Whitakker & Co.
Roosen-Runge, H. (1967). Farbgebung und Technik frèuhmittelalterlicher Buchmalerei. Studien zu den Traktaten "Mappae Clavicula" und "Heraclius." Mèunchen; Berlin: Deutscher Kunstverlag.
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