Mayos Music
Guitar Lessons and Instrument Repair

GUITAR FINISHES
WHY IS A GUITAR FINISHED?

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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?


Just 2 reasons:
  1. To preserve the guitar's wood
  2. It looks good

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.


  1. VARNISH
    First derived from tree sap (pine sap) then mixed with a solvent and applied by brush, dating to “Ancient Greek Times”- varnish is a mixture of resin, drying oil and a solvent.

    Components of solvent
    1. RESIN- sap of trees, including: amber, rosin, balsam. Also synthetic resin like phenolic.
    2. DRYING OILS- linseed oil, tung oil, walnut oil, benzoin, mastic, alkyos, etc.
    3. SOLVENTS- turpentine, mineral spirits, alcohol, etc.
    TYPES OF VARNISHES
    1. RESIN VARNISH- Dries by evaporation of the solvents and oils.
    2. ACRYLIC AND WATERBORNE VARNISH- Need longer cure periods. Hard to repair. These varnishes do not soak into the wood.
    3. OIL, EPOXY VARNISHES- Long cure period.
    4. SPAR VARNISH (AKA MARINE VARNISH)- Very elastic and water resistant. Not good for musical instruments because of their softness which absorbes and thus mutes vibrations.
    5. POLYURETHANE VARNISHES- Formulated from polymers, have a thick film build, not good for musical instruments.
    6. TWO-PART VARNISHES- An epoxy varnish with limited bonding properties as they do not soak into the wood and are hard to repair.
    7. CONVERSION VARNISHES- a two-part system, mostly used in furniture and cabinet work.
  2. SHELLAC
    Shellac, with an ancient history over 3,000 years, is derived from a resin-like substance called “lac” that is secreted from an insect called “laccifera lacca” (origins: Thailand, India, and Persia). Shellac is non-toxic and has many uses other then wood finishes.

    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:

    1. Non-yellowing
    2. Good adhesion
    3. Good sealer (moisture vapor barrier)
    4. Very hard- won't dampen vibration of soundboard
    5. Easily repaired
    6. Non-toxic
  3. FRENCH POLISH
    French polish is a process, the technique that applies many coats of shellac in thin layers. (See Shellac)

    Today, used most frequently on very expensive classical guitars.


    PROS:

    1. Very high gloss finish
    2. Believed to enhance the tone of the instrument as it is very thin and flexible

    CONS:

    1. Requires the most care
    2. Poor resistance to water and scratches

  4. TUNG OIL

    An oil refined from the dried nuts of the Chinese tung tree, references from 400 BC.

    Tung oil is a penetrating oil.


    PROS:

    1. Can be used on the guitar neck- many players like the feel
    2. Also a good finish for furniture

    CONS:

    1. Not good for the musical instrument's body and soundboard as it dampens the vibrations and singing quality

  5. LACQUER

    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.


    PROS:

    1. Touch-up and finish repairs are easier than other finishing systems
    2. Faster to apply and more durable than French polish
    3. Very high gloss when buffed
    4. More resistant to scratches, body heat, moisture than shellac finishes
    5. Doesn't clog the wood pores
    6. More resonant than newer/thicker poly type finishes

    CONS:

    1. Has a tendency to crack, craze or check when exposed to sudden low temperatures
    2. Will crack if applied too thick
    3. Body oils and sweat can chemically change lacquer and turn it permanently soft
    4. Sensitive to vinyl (guitar straps) will turn soft and blister
    5. Softer and more fragile as compared to poly type finishes

  6. POLYESTER FINISHES

    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.


    PROS:

    1. More durable and less prone to aging and fading as compared to nitrocelluilose lacquer
    2. Excellent filling properties and doesn't sag or crack easily

    CONS:

    1. A thicker finish that will dampen the tone and sing quality of an acoustic guitar

  7. POLYURETHANE LACQUERS

    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.


    PROS:

    1. More durable than nitrocellulos lacquer

    CONS:

    1. Will clog the wood pores- mutes the tone and sing quality
    2. Hard to repair or touch-up the finish

  8. ACRYLIC LACQUERS

    Developed in the 1950's and derived from acrylic acid. Acrylic resins (synthetic polymers) used in lacquer. Great shine without need of buffing.


  9. CATALYZED LACQUER:

    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.


    PROS:

    1. Dry/cure quickly
    2. Very durable- resistant to cracks, crazes, scratches
    3. Environmentally friendly

    CONS:

    1. Once cured, there is no solvent that will dissolve the finish
    2. Not easily repaired

  10. WATER BASED LACQUER

    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.



Final Word

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



Experience since 1968
Providing Guitar, Electric Bass & Ukulele lessons and Guitar/Amp Repair in the Greater Phoenix Valley area of Arizona including Maricopa County and The Salt River Valley.

Mayos Music will continue to provide Guitar/Amp Repairs in Southern California's South Bay cities and Greater Los Angeles Area.
Originally located in Manhattan Beach and Torrance, California.

Now located in:
Gilbert, AZ 85298
&
Torrance, CA 90505

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