Wednesday, April 7, 2010

Types of Guitar Finishes

I am going to attempt a quick run down on the types of guitar finishes that have been used and or wood finishes that ultimately found the way to musical instruments.
The oldest finish is Shellac. Shellac comes from a resinous substance that a bug called Laccifer lacca secretes to form a cocoon for its larvae. The cocoon is the raw material from which Shellac is derived. The Laccifer lacca is indigenous to India and Thailand. The recorded use of shellac for finishing dates back to 250AD. Shellac is used for French polishing and it dissolves well in denatured alcohol. The method of finish was widely used until the 20th century. Shellac like hide glue might be something you have consumed as it is used for pill coatings.

Nitrocellulose lacquer is derived from a plastic dissolved in volatile organic compounds (VOC ) such as butyl acetate, toluene, and xylene. Nitrocellulose resin is obtained from nitration of cotton and other cellulostic materials. Nitrocellulose was invented in the 1920's so it's history is not a deep as Shellac but its primary use was for automobile paint. The quick curing properties saved production time and time is money! Nitrocellulose can be buffed to a higher degree of shine, producing a harder more flexible finish sharply contrasting Shellac. In addition, Nitrocellulose is more resistant to sweat and body oils than Shellac. The drawback to Nitrocellulose is it's volatile nature. It's flammable nature and toxic manufacturing process make it not such a green choice of finish material. As nitrocellulose ages it looses its voc's that make it flexible and with age the finish becomes brittle. The cool thing is that nitrocellulose is an evaporative finish that can be redissolved and refinished to repair the aged imperfections.

Catalyzed Polymer finish utilizes properties very similar to expoxy. Not all catalyzed finishes use a two part convention. The most popular of catalyzed finish uses a light sensitive curing agent. Once applied the material remains in a liquid state until it is exposed to a light source of varying wave lengths. Once exposed the material cures very quickly to a hard inert finish that buffs well, resists body sweat, body oils, scratch resistant and is very durable. This finish has no susceptibility to vinyl or rubber. Many people associate this type of finish with low cost production guitars because of its ability to cover imperfections in wood. However, some very reputable luthiers are now starting to use this very method on their finest instruments. The thickness of the finish can be control well with current procedures thus making for a very durable instrument finish that will outlast nitrocellulose. The problematic area of this finish is that if you need to refinish the instrument. No solvents will melt this material. Chips must be repaired with cyanoacrylate glues catalyzed by moisture. This material matches the polyester in hardness and durability but never quite blends into the finish thus leave a bit of a haze. The good news is that the polyester is far more durable than nitrocellulose and shellac so there is far less need for touch up.

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