Spirit Varnishes
The old types of spirit and volatile oil varnishes, such as shellac and dammar varnish, are still used for numerous purposes. They are made cold or without great heat by dissolving the resin in its best solvent, such as grain alcohol for shellac and turpentine or more commonly a turpentine substitute for dammar and mastic.
Shellac substitutes, which are cheap, inferior finishes, also belong in this group if they contain alcohol as a solvent. Some of the new synthetic gums similar to those used in lacquers are also soluble in volatile oils and varnishes from them belong in this group because they dry by evaporation, which is ideal for wood plinth blocks, wooden bar rails, or wood door toppers.
The user of shellac 40 or 50 years ago bought orange flake shellac in the form of thin scales varying in size up to about three-quarters of an inch in diameter. wood alcohol was the solvent which the shop finisher used in preparing his orange shellac. White shellac was made from
chunks of bleached shellac which dissolved with difficulty in wood alcohol, especially if the shellac was old and had been exposed to the air for some time.
Today, either orange or white shellac in liquid form of various strengths dissolved in denatured grain alcohol can be obtained from almost any dealer in finishing supplies. Some of the cheaper liquid shellacs of today are made with a solvent which is a mixture of grain and wood alcohol. Such shellac produces a disagreeable odor when it is being applied.
Shellac varnishes may be thinned with cold denatured alcohol and can then be used in a very short time. Coatings of shellac varnish dry very quickly and produce a low gloss or semi lustrous finish. Shellac varnish is often used on floors, corner guards, plinth blocks, door toppers, and for some other similar wood finishes. Shellac coatings will turn white if exposed to the weather or spotted with water.
Contractors often prefer shellac as a floor finish because it is easy to apply, dries quickly, and produces a good effect. Shellac is generally unsatisfactory for floors because it does not wear long or well and turns white if water comes in contact with it. Shellac, somewhat diluted, is often used for an undercoat or as a sealer. It should be sanded well before another finish is applied over it in order to secure smoothness and aid in the adhesion of the next coating.
Oil Varnishes with Linseed Oil
Varnishes made from fossil resins, ester gum, or treated rosin, which can be melted to liquid form at great heat and then combined with linseed oil in large part, have been the standard slow drying varnishes that have been in use in some of their forms for centuries. Metallic driers of several types have usually been added in small amounts to speed-up drying or oxidation.
An excess of drier cannot be added to increase the drying speed even for wood surfaces such as window toppers, fireplace mantels, or even plinth blocks because of various difficulties that are impossible to overcome. In the old oil or oleoresinous varnishes, turpentine was placed in the mixture as a thinner or volatile solvent; but, for some years, this excellent solvent has been replaced very largely by some mineral spirit or a cheap petroleum volatile oil.
It is through the evaporation of the thinner or solvent and the slower changes in the drying oil, which the chemists say is largely oxidation that a linseed oil varnish including fossil resins dries out and changes from a liquid to a solid film. There is a rather marked chemical change during the oxidation of drying oils, such as linseed oil, and the new substance formed has molecules which contain additional atoms of oxygen.
The oxidation of a varnish film begins at the surface, which forms a skin on the outside and dries out more slowly inside because of greater difficulty in obtaining oxygen from the air about the film. For fireplace inserts, ornamental pediment, and wood fireplace mantels, this is ideal due to the necessity for quick drying on the immediate surface. The standard thinner for practically all of the high grade oil varnishes of the hard fossil gum type was turpentine, which almost entirely dried out by evaporation, leaving only a very small residue.
Other volatile thinners have more recently been substituted for turpentine with success since Congo resin and kauri have become scarce and expensive and other resins have replaced the hard fossil resins at least in part.
Great variations in the speed for drying of linseed oil varnishes made with hard fossil gums are possible. Quick drying or four-hour varnishes, however, are not produced from these materials. The drying times of most fossil gum varnishes vary from about two days to about a year.
The very slow drying type is sometimes used on fish rods in order to secure a very flexible finish. Heat treatments of the linseed-oil produce great changes in the oil, and variations in the speed in drying of varnishes made from oils of different heat treatments are very great.
Tags: ornamental pediment | ornamental pediment | fireplace mantels | fireplace mantels | fireplace inserts | fireplace inserts | wooden bar rails | wooden bar rails | window toppers | window toppers | plinth blocks | plinth blocks | door toppers | door toppers | wood
April 28th, 2009 at 6:21 pm
the flooring in our house is about 80 years old and needs to be resealed, but i am a believer in polish, what sealer can i use to seal the floor after sanding but still be able to use a wax polish afterwards.