Wax

The true waxes, unlike the oils described in Chapter V, are not glycerides, and do not therefore yield glycerin when they are saponified - that is, turned into soaps by the action of alkalies. Ordinary beeswax is the best known, and probably the most important of all the different kinds; but very few experiments have been made as to the utilization of exotic and vegetable waxes in the processes of painting. Crude beeswax requires purification and bleaching in order to fit it for artistic use. The first operation consists in melting the wax at nearly the lowest temperature possible, and then pouring it in a slender stream into a cold saturated solution of alum, agitating the latter all the time. The granulated wax thus prepared may be bleached by exposure for several days on linen cloths to the action of the sunlight and dew; or it may be treated with dilute chromic acid solution, or with hydrogen peroxide. All these processes succeed better when the wax is in the form of thin sheets or ribbons.

The bleached wax, after thorough washing and drying, is to be re-melted. Its hardness is increased and its melting-point raised by the above treatment.

Bleached beeswax melts at 62° or 64° C. (144° or 147° F.). It consists of four distinct substances, not present in all samples in the same proportions. By boiling wax with strong alcohol a substance called myricin (myricyl palmitate) is left undissolved. The dissolved portion is the larger; the bulk of it, which crystallizes out as the alcohol cools, was formerly called cerin. It is a mixture of two fatty acids. The cold alcohol still retains a small quantity of a fourth substance.

Beeswax, by long-continued exposure to atmospheric influences, disintegrates and partially perishes by oxidation. It is a constituent of Gambier-Parry's spirit-fresco medium, into which it is introduced in order to impart a matt appearance to the painting. Excellent examples of the use of melted wax as a binding material for pigments may be seen in the National Gallery and the Victoria and Albert Museum. They are encaustic portraits, executed probably in the second and third centuries of our era, and were discovered by Professor W. M. Flinders Petrie, in the Hawara Cemetery, Fayum, Egypt. The pigments were mixed with wax and laid on in the melted state. The wax having become disintegrated in the course of centuries has been re-melted, some fresh wax having been added in several instances.

Wax is abundantly distributed in the vegetable world; its production is, in many cases, stimulated by the attacks of insects. Thus, Chinese wax is produced by the puncture of Coccus Pela, living on Ligustrum lucidum and Fraxinus chinensis. Chinese wax, which melts at 82° C. (180° F.), consists almost entirely of cerotyl cerotate. Brazilian or Carnaüba wax occurs naturally in thin films on the leaves of a palm (Copernicia cerifera); it melts at 84° C. (183° F.). Japanese or Ibota wax is probably produced by the attacks of a coccus on Ligustrum Ibota; it melts at 42° C. (108° F.).