(Pekovich, Michael, Fine Woodworking, #141, pp 58-63)
Used on top of other finishes to polish,
Also used for lubricating and sealing iron surfaces in the shop
Change from a liquid into a solid through polymerization
Penetrating finish, meaning they penetrate the fibers of the wood and harden making them much easier to apply
Three types of oils are used for finishing furniture,
-Boiled Tung oil - paler in color and has better moisture resistance
-Boiled Linseed oil - more available
-Mineral oil - used for food surfaces
-Most durable finish that can be easily applied by the beginner
-Surpasses most other finishes in resistance to water, heat, solvents and other chemicals
-Composed of synthetic resins which are thinned with drying oils
-not easy to repair
Long oil varnishes contain a higher percentage of oil and are softer, but more elastic and therefore better suited for exterior use where wood will expand and contract but not need a super hard shell.
Medium oil varnishes comprise most interior varnishes on the market.
Short oil varnish is baked on in an industrial setting.
Types of resin
Alkyd -- standard all-purpose interior resin
Phenolic -- usually mixed with Tung oil is predominantly for exterior use
Urethane -- also called polyurethane has better resistance to heat, solvents and abrasions
Oil and Varnish Blends-
Easy application of true oils, but more protective
Examples include: Watco brand Danish oil, Teak oil, Waterlox
A natural resin made from cocoons and refined into flakes, then dissolved in ethyl alcohol to make a spreadable solution.
Can be purchased as flakes or pre mixed.
Should not be used where furniture will come in contact with water or alcohol
Spoils over time, not a very long shelf life.
Dries fast, very rich and clear, very durable
Types of Lacquer
Nitrocellulose - most common, if the label just says lacquer this is probably what it is
Made from alkyd and nitrocellulose resin
Moderate water resistance
Sensitive to heat and certain solvents
Yellows with age
Acrylic modified lacquer - same properties as nitrocellulose, but will not yellow
Catalyzed - a much more complex mixture with a catalyst that initiates a chemical reaction, forming a durable finish. Once mixed, catalyzed lacquers have a short life
Pre-catalyzed - pre mixed by the distributer
Post-catalyzed - you mix two components before you spray
Contain the same or similar ingredients but the vehicle (solvents that suspend the polymers) is replaced by water.
Wax, shellac and lacquer will be damaged if left exposed to water long enough.
Wax, shellac and lacquer scratch easily, but rub out well (can be easily fixed)
Wax is very resistant to acids and ammonia, but aside from that it is least durable
Shellac is not resistant to ammonia or alcohol
Oil based polyurethane is the most durable finish you can apply by hand
Catalyzed lacquer and varnish are the most durable sprayed finishes
In a dusty environment use lacquer (dries fast) or shellac or oil (penetrating)
Shellac and lacquer are more adaptable for a wider range of temperatures
Oil dries slow in humidity and cold temperatures.