Here at MayosMusic, in addition to offering great guitar, bass, ukulele, banjo and autoharp lessons, plus complete luthier services that include guitar, string instrument and amplifier repair/restorations, we are also a great resource service.
Below is a discussion on guitar finishes including: 1) Why is a guitar finished, 2) Type of finishes used and the historical dating of some of these finishes, 3) The pros and cons of the different finishes and 4) the “never ending debate” these different finishes have on the instrument's tone and singing voice quality.
Why Is A Guitar Finished?
The following is an overview of the different types of wood finishes used on the guitar, including some pro's and con's to some of these finishes.
Please note that the effect the finish has on the tone or sing quality of a guitar is in reference to the acoustic guitar primarily.
For wood finishing (musical instruments), shellac is sold in a flake-form and must be dissolved in either: ethnol, denatured alcohol, methanol, butyl or prophl alcohol.
Advantages That Apply To Musical Instruments:
Today, used most frequently on very expensive classical guitars.
An oil refined from the dried nuts of the Chinese tung tree, references from 400 BC.
Tung oil is a penetrating oil.
NITROCELLULAR LACQUER was developed in the 1920's by Dupont.
Nitrocelluilose (a resin) is derived from the nitration cellulosic materials (i.e. cotton). The soluents (i.e. toluene, xylene, acetone, etc.) of nitrocelluilose lacquer are very toxic and highly flamable.
Developed in the 1930's by Wallace Carothers (and patented). Can be polished to a very high gloss and is very durable. Because of a high build-up of film thickness, this type of finish mutes the sing quality of an acoustic instrument. Also, no easy way to repair this type of finish.
A two-part system that hardens with the use of a catalytic reagent and is tougher and more chemically resistant than acrylic lacquers, developed in the mid 1930's in Germany. A more plastic based finish.
Developed in the 1950's and derived from acrylic acid. Acrylic resins (synthetic polymers) used in lacquer. Great shine without need of buffing.
Developed in the 1990's and is composed of urea melamine or urea formaldehyde, plus alkyd with some nitrocelluilose resin. Needs an acid catalyst and comes in 2 versions.
1) Pre-catalyzed lacquer- the components are premixed.
2) Post-catalyzed lacquer- a 2-part system that the user must mix.
Water based lacquers, developed in the 1990's are normally made from an acrylic resin and/or acrylic polyurethane mixture. As such, they share some of the same ingredients with varnish and lacquer but without harsh solvents.
So where does all of this information bring us to as of today?
First off, virtually all of the Asian guitar factories and many of the modern American makers (i.e. Taylor, Ovation, Tacoma and Martin's lower period models) use catalyzed polymer finishes.Martin's higher end models usually have lacquer on the bodies and many with catalyzed polymer finish on the necks. Gibson uses nitrocelluilose lacquer on their USA acoustic guitars.
Smaller makers (i.e. Santa Cruz, Collings, Goodall, and most individual luthiers) still use nitrocelluilose lacquer. This is mostly because nitrocelluilose lacquer is a preferred traditional finish for fine flat top steel string guitars, and because larger factories are better suited to applying catalyzed finishes.
Because of the highly prized vintage intruments (including their repair and restoration) and the construction of new and exotic traditional instruments, plus the never-ending debate over tone, we'll have many luthiers still using many of the “obsolete” finishing techniques