In the interior of the house woods are seldom used in their natural state. The surface is covered with two or more coatings of paint, varnish, etc., which add to the wood durability or beauty. The cleaning processes are applied to the last coat of finish and must not injure this.

Soft woods are finished with paint, stain, oil, shellac, varnish, or with two or more of these combined; hardwoods with any of these, and in addition, wax, or wax with turpentine, or both with oil.

All these surfaces, except those finished with wax, may be cleaned with a weak solution of soap or ammonia, but the continuous use of any alkali may impair and finally remove the polish. Refinishing will then be necessary. Waxed surfaces are turned dark by water. Finished surfaces should never be scoured nor cleaned with strong alkalies, like sal-soda, or potash soaps. Scouring with these strong alkalies will break the paint or varnish and in this way destroy the finish.

A few drops of kerosene or turpentine on a soft cloth may be used to clean all polished surfaces. The latter cleans them more perfectly and evaporates readily ; the former is cheaper, safer, because its vapor is not so inflammable as that of turpentine, and it polishes a little while it cleans; but it evaporates so slowly that the surface must be rubbed dry each time, or the dust will be collected and retained. The harder the rubbing, the higher the polish.

Outside the kitchen, the woodwork of the house seldom needs scrubbing. The greasy layer is readily dissolved by weak alkaline solutions, by kerosene or turpentine, while the imbedded dust is wiped away by the cloth. Polished surfaces keep clean longest. If the finish be removed or broken by deep scratches, the wood itself absorbs the grease and dust, and the stain may have to be scraped out.

Fig. 20. A Sulphur Candle