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Furniture Finishing
In the latter case the air surrounding the work is filled to saturation with moisture, which is condensed on the wet film by the cooling action of the evaporating lacquer solvents. The effect is to precipitate a portion of the cotton which unless re-dissolved by the lacquer solvents reveals itself in the milky "blush." To clear up, spray on a coat of slow thinner like blush retarder, with or without a percentage of the lacquer. Lacquer Sealers, incidentally, have a greater tendency to blush than finishing lacquers because they are made "short" to sand quickly.
To prevent blushing, raise the heat of the finishing room to at least 70° F. and if necessary, change to a thinner slow enough in evaporating to stay in the film and completely re-dissolve the precipitated nitro-cellulose. Blush retarder may be added to ordinary reducers to prevent anticipated blushing, in proportion of one part retarder to three parts lacquer.
Bubbling commonly appears in the varnish film but may fail to disappear because of too heavy application, insufficient brushing or inadequately filled pores, in which air left in pockets works up to form bubbles as the varnish is setting, much as in blistering. A varnish that is green or very quick drying may also bubble. Bubbling in lacquer happens when the top film sets before the solvents have had time to escape. This results in the formation of small clouds of bubbles which are broken in rubbing, leaving them gray when the pumice dries. The bubbles are most commonly found near the edges where lapping leaves a thick film or when the lacquer itself is too heavy or made to top dry too quickly. Any lacquer which is not sprayed at the right pressure, held too close or too far away from the work or lifted near the end of the stroke, may also give this trouble.
In spraying clear or lacquer enamels hold the gun at right angles to the surface you are coating. Be sure that you are moving the gun fast enough to get a wet coat without flooding the surface at any spot. The gun must be constantly in motion. When you come to an edge keep on until just past it and return your stroke, overlapping enough to avoid skips or streaks between spreads of material.
Caking on the rubbing pad may be traced variously to insufficiently dried varnish, varnish on which dirt has been allowed to settle in drying or from which varnish skins have not been strained. It may also result from a harsh quality of pumice stone, from excessive heat generated by the rubbing machine block, coarse or "ribbed" rubbing felt or last but not least, insufficient water or oil lubricant. If the varnish is green, liquid soap may be added to the water, or rotten stone mixed with the pumice.
