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Furniture Finishing
Finishing Troubles Cause-Prevention-remedy
WHEN trouble develops in finishing operations the first thing to look for is the root, for without this identification an attempted remedy may serve merely to make a bad matter worse. Sometimes the real cause is difficult to locate, and a gradual process of elimination is necessary, checking all possibilities one at a time.
Once the source of trouble is located definitely it is important to know whether method or material should be changed to prevent a repetition. Frequently it is necessary to remove finishes that turn bad after going in service but many troubles can be remedied before proceeding further by simply recoating.
The following alphabetical list of troubles under the name by which they are known in the trade will cover the most common difficulties encountered in furniture finishing and even a theoretical familiarity with them will help when the actual emergency arises.
Bleeding occurs when the color of a stain or filler spreads up into a succeeding coat. For example: Oil soluble aniline stains containing red will bleed into and through either clear lacquer or varnish. There is a special coater made to prevent bleeding of mahogany aniline oil stains into oil or lacquer enamel finishing coats. A non-bleeding color is one which is chemically inert or not soluble in the finish coat, i.e., water or non-grain-raising stains.
Blistering represents the formation of bubbles or pimples on the surface of the dried or drying finish coat and may be caused by excessive heat as from direct sunlight through a plate glass window or from a near-by radiator, or may also be caused by sealing wood that is slightly green, or a heavy coat of shellac over filler may seal in moisture from undried stain which expands when the finish is exposed to slightly higher temperatures and the moisture endeavors to push its way up and out.
Blooming appears as a bluish film on the surface of a varnish, lacquer or enamel film. A viscous rubbing oil, premature or excessively coarse or dry rubbing, inadequate ventilation, oil in the film from the spray line and chemical fumes are all common sources of the trouble. To remove, rub with liquid soap and rotten stone, then rinse with clean water and dry with a chamois skin. A bad case on lacquer should also be polished with brown liquid wax. Blooming differs from blushing, which takes place before the film is dry.
Blushing takes place in the film of a lacquer, shellac or shellac substitute during the course of drying when it develops a whitish milky appearance. Moisture in the air line, direct drafts, or a high relative humidity in the atmosphere, all may cause blushing.
