This section is from the book "Paint And Varnish Facts And Formulae", by J. N. Hoff. Also available from Amazon: The Industrial And Artistic Technology Of Paint And Varnish.
Gas fumes and rapid changes of temperature at the time the varnish is applied may produce the same effect.
Noxious gases and the use of too much benzine in reducing will cause varnish to turn yellow.
Varnish containing little oil and made from rosin will frequently turn white on exposure to dampness and atmospheric conditions.
Varnish will sometimes become dull or flat when applied. This flatting or deadening is due to excessive dampness, in the atmosphere, dampness of the surface to which it is applied, a porous surface, or an undue amount of dryer used in its manufacture. This deadening does not always occur immediately, but sooner or later after its application.
Good Oil Paint should contain pure drying oil of known quality and only such pigments as do not act injuriously on the oil binder. It should cover and spread well and not pull under the brush, neither should it contain an excess of thinners. It should not contain an excess of dryer and when it is spread should dry to form an elastic coat, free from imperfections.
In painting, the first requisite is to have the surface to be coated perfectly dry, free from oil or grease and in proper condition to receive the paint.
Much trouble can be prevented by taking these precautions.
Crawling or separating of paint may be caused by a greasy or glossy surface underneath, or the chilling of the paint when applied at too low a temperature.
Paint will run or adhere poorly to a surface if an excess of oil has been used in its preparation. It will draw or pull if too little oil has been used, or when applied on a poorly prepared surface. Paints containing mineral colors and the so-called neutral pigments, do not work so smoothly under the brush as white lead paints. In the latter case, the lead forms a smoothly working compound with the linseed oil.
Paint will often lose its gloss if covered with frost or moisture before it has dried. When paint is applied too heavy, it is apt to crinkle or form folds in drying. It may also sag under these conditions.
Blistering may arise from several causes, the most common of which, is moisture, which existed on the surface of the work when coated, or which was contained in the wood from water getting behind the weather boards. The heat from the interior of the building or the heat of the sun will frequently drive or draw out the moisture and where such action occurs, the layer of paint, if still elastic, loosens from the wood and forms blisters.
Sappy resinous wood will act in the same way. The use of heavy boiled oil, or thickened linseed oil has a tendency to blister when exposed to the sun's rays before the coat is perfectly dry and hard. Paints which are too elastic and pliable are liable to this trouble.