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Coloring Finishing And Painting Wood
A complete list of the various qualities of varnishes would be long, and a discussion in detail about them would probably not be profitable in these pages. A list of the chief qualities will be of interest to some readers, also a few brief remarks about some of them. Among the most important qualities are: good working and flowing properties, hardness, color, drying time, viscosity, moisture and gas proofness, weather exposure test for one year, also resistance to hot or cold water, gasoline, and acids or alkalies; clear transparent color, proper body, sufficient elasticity, and exemption from both checking and flatting.
Experience has shown that flat varnishes show a cloudy effect, especially when they are placed over very dark woods, such as walnut or mahogany, or over woods stained in these colors. In fact, it has been found that flat varnishes do not furnish as clear and transparent effects as come from clear-varnish, rubbed finishes. Another objection to flat varnish is that it is less waterproof than are clear varnishes in general. Usually the use of flat varnish is satisfactory for inside use because it is applied only as a final coating, the other coats being of more waterproof gloss varnish.
"Aging," which was formerly thought to be of great value in varnish-making, is still practised unless the varnish is forced thru a press filter. It has been found that one important advantage of '' aged'' varnish is that it is clearer because thru a period of a few months in tanks a certain amount of very finely suspended matter remaining in the varnish undissolved gradually settles, leaving a clear varnish which is better for use. At present some manufacturers have a system of press-filtering their varnishes which clears them about as well as storage and aging. Because it has been found that the important properties or qualities of varnishes remain largely unchanged by aging and that press-filtering will remove the small particles that usually settle if given time, it has been decided that aging is not as important as it was formerly thought to be. Aging seems to remove fine sediment thru settling, but the other propertics which are important, such as durability, drying, waterproofness, body, and working qualities, seem to remain unchanged by storage and aging.
In addition to precipitation of solid impurities that will never dissolve, other effects may be possible in some kinds and grades of varnish. Ripening thru aging is thought to be of real value for high-grade varnishes, especially for use on automobiles, coaches, and for architectural work. It is thought that in some types of varnish the chemical reactions in the liquids are slow and that there may be gradual changes, partly physical and partly chemical, thru a period of months. There also may be some evaporation of rather volatile liquids which will change the varnish in some respects.
