The Encyclopedia Americana (1920)/Varnish

VARNISH. A solution of gums or resins which is applied to the surface of objects to afford a glaze and protect the article so coated. Its use is largely decorative and applied to enhance the appearance of woodwork (furniture and house fittings) as it brings out the beauties of the grain and color of woods more distinctly and permanently and at less cost than the process of polishing, being applied with a brush similarly to painting. Varnish is also used, as an upper or outside coating of paint to enhance and make more permanent the pigments. The ancient Egyptians were acquainted with the art of varnishing, but its origin appears to have arisen in the East. In India, China and Japan the practice of lacquer work, a species of varnish application, was known at a very early date. It has been claimed that Japan was acquainted with the art of lacquering 500 or 600 B.C., but the majority of authorities place its first usage there to the 3d century of our era, as an art acquired from their neighbors the Coreans. The natives of China and India probably knew the art much earlier than the Japanese. Varnish and lacquer work are, however, generally treated in the arts as separate and distinct. True varnish does not appear to have been known in Europe till the 17th century.

A practical varnish will cover the following requirements: It must be a homogeneous fluid or solution; must be fixed or permanent in effect as to tone of color, transparency (or opaqueness), and must, on application in thin layers by brush or otherwise, dry within a short period by evaporation of its volatile solvents (alcohol, ether, benzene, spirits of turpentine, etc.), leaving a film of smooth, lustrous (sometimes purposely dull), elastic oil and resin, impervious to its surrounding atmospheric conditions. It must when dry be free from cracks or flaws. In general varnishes may be divided into natural, oil, spirit and water varnishes. Natural varnishes so called are the group of lacquers as used in India, China and Japan and are produced in liquid form by nature as the saps or juices of trees (Rhus vernicifera). They are generally treated under the title lacquers (to which refer) and will not be considered here. Oil varnishes: These are a product manufactured from linseed oil, gum resins, driers, and a solvent such as turpentine or white spirit. The gums are largely fossil resins. Oil varnishes in commerce are frequently divided into the two general classes: carriage varnishes and cabinet varnishes; both are of very similar character as to composition and manufacture, but the best and most durable for open air use are selected as carriage varnishes, the remainder being termed and used as cabinet varnishes. Spirit varnishes consist of a kind made from various resins dissolved in a volatile spirit — methylated spirit (grain alcohol denaturized), turpentine, etc. They are generally made without oil, but some have a small admixture of oil. Water varnishes find but small application in the industrial arts. There are lac water varnish, glazing varnish, glue varnish and crystal water varnish. The first makes a good paper varnish and is used on harness, as is also the glue varnish.

Materials used in the manufacture of varnishes may be placed under the following groups: drying oils, resins, gums, solvents and coloring matter. Good drying oils are made from old linseed oil of the best quality (best Baltic preferred). It should be aged at least a year before use by being stored in containers exclude any attack of the air. While the difference between raw and old stored oils is great, the cause is not known to science, nor have the chemists discovered the reactions caused in ageing. The selection of resins in the ingredients employed is more important than any other, for the lustre and permanence of the products depends absolutely on the qualities of the resins used. Gums as known in commerce are the exudations from trees and consist of what are termed water soluble and spirit soluble. The water soluble gums are of course not correctly used in varnishes as it is required that varnishes shall not be affected by water. For varnishes the resins available for the commercial markets are: amber, kauri, copal, dammar, shellac, mastic, sandarac, benzoin, elemi, animi, pine resin (rosin), asphaltum. Most resins come to the market either in the form of knotty masses, drops, cylindrical pieces or blocks. lit the factory the gums are divided into classes as follows: oil varnish gums, as amber, animal, copals, sandarac, rosin and kauri. Ethereal varnish resins are: all oil resins after they have been fused; dammars, mastic, sandarac, rosin, Manila copal. Spirit varnish gums are: lac, Manila copal, sandarac, mastic, rosin, melted resins. The points or characteristics to be considered are hardness, fusibility, solubility, appearance, color. The resins mentioned under oil varnish are insoluble in oils, ether and other solvents, until liquified by fusion; rosins, some soft copals and sandarac are exceptions being soluble in alcohol. The gums grouped under ethereal varnish are more or less soluble in benzol, coal-tar naphtha, turpentine, ether, acetone, etc. The enumerated spirit varnish gums are soluble in alcohol and methylated spirit. Natural coloring matters used in varnishes are: turmeric, gamboge, dragon's blood, gum accroides, aloes, etc. Some artificial or coal-tar colors also enter into the manufacture of varnishes.

Manufacture, Oil Varnishes. — The plant for this class is very simple as is the process, but carrying out of the process requires very great care and experience to produce a commercially successful line. The stages of the process are: (1) melting or running the resin and gums; (2) boiling the oil; (3) mixing the melted gum and boiling oil; (4) boiling the varnish; (5) thinning the boiled varnish; (6) clearing. The gum running is a very delicate operation and the finished varnish depends entirely upon the successful outcome of this process. It is done in a large cylindrical copper vessel, with flat or domed bottom known as the “gum pot.” These pots have flanges near the bottoms which support them in the holes on top of a furnace. In modern varnish works the furnace top is flush with the floor of the gum running shed. These pots have wheels appended to ease movement from the gum running shed to the mixing shed. The pots have hood-covers which connect with flues by stove pipes to allow vent for the noxious vapors. During this running process oil is being boiled in a boiling pot, the oil heated to 500° F. for from one to two hours. The gum is run by heat till it has a steady boil without frothing (which occurs at the start and is the chief source of danger — that of running over). The boiling oil is then added in the correct proportion and thoroughly mixed. The mixture is then poured into a “set pot.” The mixed oil and gum are now boiled together to get it thoroughly homogeneous. The set pot is an iron vessel formed like a washing boiler and with a capacity of some 600 gallons. It is set in a specially constructed furnace to hold it. With several runs in it the mixture is boiled at a temperature of from 450° to 500° F. for a time varying from half an hour to four or even five hours, according to the kind of varnish. It has now become a viscous mass and should be clear and transparent. While in the former process the danger was from boiling over, the danger in this process is that of catching fire. For extinguishing such should the material become enflamed, a shallow pan-shaped cover filled with sand is suspended above the set pot ready to let down and smother the fire. The next process is that of thinning. This is done by removing the set pot of boiled fluid outdoors away from any furnaces or flames where it is mixed with the turps till acquiring the necessary consistency. The next process is the necessary clearing and aging, as freshly made varnish works badly. This process is performed by placing the material in large iron tanks or cisterns and, after hermetically sealing, storing for six months to two years. In this period the insoluble matter slowly precipitates and leaves a clear fluid.

Spirit Varnishes. — These can be made with the same plant as the oil varnishes. The French process is very similar to the procedure given for oil varnishes, the main difference being that these varnishes contain little oil. They are made by running the gums, mixing with oil previously brought to a boil and the mixture boiled till stringy (viscous); after which the mass is cooled and mixed with spirits. In the “common” process the resins are mixed with the solvent and kept in a warm place or heated slightly till the gums are dissolved; therefore, permitting only spirit soluble gnms to be used.

Water Varnishes. — These are produced as follows: Lac water vamish contains the proportions of six ounces shellac to one and one-half ounces borax boiled together to each pint of water. Glazing varnish is made with a mixture of egg-white and water preserved by the addition of a little carbolic add or thymol. Dissolved albumen can take the place of white of eggs. Glue varnish is a solution of the proportions of one pound pale glue to every two gallons of water. The quality and color are dependent, of course, on the land of glue used — white, brown, etc. It is not water proof and has the defect of being sticky, but is less permeable to water if a little bichromate of potash be added to the ready-made varnish, not during the process of manufacture. Crystal water varnish is produced by dissolving, in the following proportions, one pound of good white gum arabic to one pound of glucose to each three pints of water.

In commerce the different varnishes are known as finishing body varnish for coaches, hard drying or flatting varnish, elastic carriage varnish, elastic hard carriage varnish pale oak varnish, oak varnish, hard church oak varnish, pale copal varnish, japanners' gold size, black japan, black varnish for carriage iron work, Brunswick black, gold size, balloon varnish, black leather varnish, amber varnish, copal picture varnish, oil varnish, bookbinders' varnish, patent leather varnish, photographic varnish, etc.

Bibliography. — Heckel, G. B., ‘A Varnish Catechism for Varnish Men,’ (Philadelphia 1912); McIntosh, J. G., ‘The Manufacture of Varnishes and Kindred Industries’ (London 1911); Bottler, M., ‘German Varnish-Making’ (New York 1912); Hurst, G. H., ‘Painters' Colours, Oils and Varnishes’ (London 1906).