Woodworker's Journal 1985-9-1, страница 15

Restoring Antiques

Shellac

by John W. Olson

Over the years, shellac has been one of the most widely used of all the clear final finishes. It is a natural material, derived from the resinous secretion of a Southeast Asian insect commonly called the lac bug. The lac bug lives and breeds in trees, and the secretions of countless insects eventually accumulates on the branches. Each year, the branches are harvested, and the secretions processed to form shellac.

Shellac can be purchased in the form of flakes, or mixed with a solvent (usually denatured alcohol) to form a liquid. Most hardware stores carry it in the liquid form. The flakes are generally sold by mail order outfits that specialize in finishing supplies. You'll find several of these suppliers iisted in the Cabinetmaker's Supplies column in our July/August 1984 issue.

Shellac has several advantages. It goes on easily and dries quickly, resulting in a flexible finish that polishes well and is quite durable. However, it has some disadvantages that should be kept in mind. It is not heatproof, so a hot dish will melt the finish. It is not waterproof, so a wet glass will leave a white ring (which can usually be rubbed out but not always). If it is applied on a humid day, the finish may develop a milky white appearance. And finally, since aicohol acts as a solvent with shellac, an alcoholic drink that's spilled on shellac will dissolve the finish. All the above factors taken into consideration, it is not a good idea to use shellac on a table top that will be exposed to heat, water, or alcohol,

The number of pounds of shellac flakes dissolved in one gallon of solvent is called the "cut," A four pound cut means that four pounds

of flakes were dissolved -Shellac Dilution Table

in one gallon of solvent. The label on the can will tell you what the cut is— most hardware stores carry four pound cut. At the time of application, a four pound cut is usually thinned to a two or three pound cut. The table shows the formula for thinning three, four and five pound cut shellac.

Hardware stores generally carry both orange and white shellac. Orange is the natural color of shellac, and when applied to wood, it results in an amber tone. For this reason, orange shellac is best used on dark wood, or wood with a dark stain. White shellac is produced by bleaching orange shellac. For light woods, where an amber tone is undesirable, white is the best choice.

Because shellac has a limited shelf life, the manufacturer will stamp the can with an expiration date. Due to the bleaching process, white shellac has a shorter shelf life than orange. Shellac that's too old won't dry properly, leaving a tacky finish that will never harden. So before buying, check the expiration date, and don't buy more than is needed for the job. \\wj

Original Cut 51b. 51b. 51b. 41b. 41b. 4 lb. 3 lb. 31b.

Desired Cut

31b. 2 lb. 1 lb. 3 lb. 2 lb. 1 lb. 21b. lib.

Parts Alcohol 1 1 2 2

3 2 2

4

Paris Shellac 2 1 1 1

4 1

5 3

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