Manufacture, Oil 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 corn mercially 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) Bearing. The gum running is a, very delicate operation and the finished varnish depends en tirely upon the successful outcome of this proc ess. 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 be ing 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 pro portion 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 cis terns 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 be ing 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 ocommon)) 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 gums to be used.
Water Varnishes.— These are produced as follows: Lac water varnish contains the pro portions of six ounces shellac to one and one half ounces borax boiled together to each pint of water. Glazing varnish is made with a mix ture of egg-white and water preserved by the addition of a little carbolic acid 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 kind 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 bichro mate of potash be added to the ready-made varnish, not during the process of manufac ture.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 pic ture varnish, oil varnish, bookbinders' var nish, patent leather varnish, photographic var nish, 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 New York 1912) ; Hurst, G. H., Colours, Oils and Varnishes) (London 1906).