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.).

Paraffin wax, hard paraffin, solid paraffin, and ceresin, are names given to certain mixtures of hydrocarbons occurring in native petroleum and in the 'mineral wax' called ozokerite, and also in the tars produced by the destructive distillation of wood, peat, lignite, bituminous shales, and coals. The liquid hydrocarbons which accompany the paraffin wax are described so far as necessary in Chapter XI (Siccatives Or Dryers). under the head of Solvents.

Paraffin wax, so far as its main or fundamental constituents are concerned, contains no oxygen, and is a mixture of several of the least alterable of all organic compounds; very few chemical reagents have any action at all upon it. On this account it presents for artistic purposes a marked superiority over beeswax or any vegetable wax. Of the hydrocarbons occurring in large quantity in paraffin wax the best known are those to which the chemical formulæ C22H46, C24H50, C26H52, C27H56, C28H58, and C30H60 belong. The melting-point of paraffin wax oscillates within wide limits, say, from 30° to 80° C. The higher the melting-point the harder, the heavier, and the less crystalline is the material. For artistic purposes, hardness and the absence of a tendency to separate from solution in the form of large crystals are desirable properties. Unfortunately the hardest paraffin waxes of high melting-point are much less soluble in oils, terpenes, and varnishes than the softer varieties, and thus their usefulness is limited; they are also somewhat yellowish in hue. I have, however, found that a pure paraffin wax from the Bathgate shale, having the melting-point of 65.5° C. (150° F.), answers every purpose.

It is sufficiently hard and but indistinctly crystalline, and yet may be dissolved in fair abundance by the usual solvents. It is convenient to preserve it for use in the form of small flattened globules, which are easily prepared by melting the substance and pouring it drop by drop on to the surface of a large sheet of glass previously moistened by breathing upon it. When these drops are shaken in a bottle they rattle like small pebbles, and do not mark the glass; when the softer solid paraffins are thus treated, they fall with a thud, and leave streaks and spots upon the interior surface of the vessel. This difference of deportment affords a ready means of distinguishing between a paraffin wax suitable for artistic uses and one which had better be rejected.

The manufacture or isolation of hard paraffin and its purification are not described here. The processes employed - distillation, treatment with oil of vitriol, fractional crystallization from solvents, etc. - involve the use of complex apparatus. It may, however, be here stated that commercial hard paraffins vary somewhat in purity. Those obtained from mineral wax or ozokerite are nearly free from oxygen compounds; while those derived from the products of the destructive distillation of shales, coal, etc., sometimes contain as much as 3 per cent. of oxygen, indicating the presence of other bodies besides hydrocarbons. Some of these bodies are of an acid nature; these may be separated by repeatedly boiling the commercial paraffins in question with a 5 per cent. solution of caustic potash. The following table shows the relations subsisting between the melting-point and the specific gravity (at 20° C.) of six different samples of hard paraffin, generally known as ceresin, from ozokerite:

A sample of ceresin made from ozokerite was furnished to meat my request by the late J. Calderwood, of Price's Patent Candle Company. It has a setting-point of about 156° F. (69° C), and is almost non-crystalline in appearance. It possesses, however, a somewhat greasy feel and a slight yellowish hue. I find by experiment that this ceresin, with a small admixture of a refined paraffin (from the same manufacturers) having a melting-point of 147° F., forms an excellent substitute for the hard paraffin wax (melting-point 150° F.), from Bathgate shale, described on a preceding page, and unfortunately no longer to be met with in commerce.

Hard paraffin wax may be used in the preparation of painting mediums as a substitute for beeswax; for preventing the separation of heavy pigments, such as vermilion, from the oil in which they are ground; and for the preparation of certain painting-grounds.

¶ In practice it has been found that far smaller quantities of beeswax than of paraffin wax are required to prevent the subsidence of heavy pigments from the oil in which they have been ground. Moreover, the working of paints containing a small quantity of beeswax is more agreeable than is the case with those into which paraffin wax has been introduced.