Larry Johnson, age 13, of Marion, Ohio, for his question:
HOW IS VARNISH MADE?
Varnish is a transparent liquid used to protect wood, metal and other materials from air and mositure, and to improve their appearance. Both natural resins and synthetic resins are used in making varnish.
Natural resins are extracted from living plants and from fossil plants. Shellac, dammar and rosin are common natural resins. Synthetic resins include such chemical compounds as phenol formaldehyde, urea formaldehyd e, glyceryl phthalate and coumar.
In making spirit varnishes, the resin is dissolved by churning it with the solvent. Small amounts of heat are sometimes used to speed the dissolving process. After the resin is dissolved, the varnish is refined by filtering and is then ready for use.
In making oleoresinous varnishes, the oil and resin are cooked in closed kettles that hold 5,000 gallons or more. The mixture is kept at a temperature of 450 degrees to 700 degrees Fahrenheit until it reaches the desired body or thickness.
Once it reaches the proper thickness, the mixture is cooled and thinners are added.
Some natural resins will not dissolve easily in oils. These resins are run or heated at about 600 degrees Fahrenheit until 15 to 30 percent evaporates.
Drying oils are added to the varnish to hasten the drying time. Linseed oil was probably the first oil to be used in varnishes. Many other drying oils are used today, such as perilla, lung, dehydrated castor, soybean and fish oils. Compounds of lead, cobalt or manganese are often added to quicken drying.
Varnishes are named by giving the number of gallons of oil that have been mixed with 100 pounds of resin. For example, a 30 gallon lung oil kauri varnish is made with 30 gallons of lung oil and 100 pounds of kauri resin.
Varnishes used on surfaces exposed to weather contain more oil than those used indoors.
There are two main classes of varnishes: spirit and oleoresinous.
Spirit varnishes are made of chemicals called resins. The resins are dissolved in a quickly evaporating solvent such as alcohol. These varnishes dry when the solvent evaporates. Shellac is a common spirit varnish. Other spirit varnishes include Japan, dammar and pyroxylin lacquers.
Oleoresinous varnishes are mixtures of resins and drying oils that are heated and dissolved in turpentine or petroleum products. These varnishes dry in two ways: by evaporation of the solvent and by hardening of the resin oil mixture when it combines with oxygen. Oleoresinous varnishes withstand outdoor conditions well. Spar varnish, used on the wood exterior of boats, is an oleoresinous varnish.
Clear varnishes protect the surface of wood while allowing the natural grain of the wood to show through. Varnish stains contain dyes that change the color of the wood but still bring out the grain.
Varnishes used on metal are sometimes called lacquers. Lacquers help prevent corrosion without dulling the metallic appearance.
Varnishes are also used to protect insulating wires, masonry and paper from moisture.