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Guitarists' expectations regarding finish on
their guitars have long been guided by the oldest
widely used guitar finish of all, French polish.
French polish has a number of advantages for guitars—
- It can be applied in a thin build.
Thinness is a universally valued finish property
among guitarists for optimal acoustic benefits.
- It will dry and cure on rosewood.
Varnish applied without a shellac sealer will
never dry on rosewood; it will remain tacky
forever because of the unique properties of the
wood resins.
- The French polish application technique
makes possible a smooth finished surface without
the need of any tools other than the cheesecloth
bun (called a "rubber") used to apply it.
The technique can also fill the notoriously
large pores in rosewood to near-level.
There are several serious problems with French polish—
- It's very delicate in terms of abrasion
resistance and doesn't wear well at all.
- It is vulnerable to all sorts of chemicals,
starting with water, human perspiration,
alcohol, etc.
- The technique is monumentally time
consuming. French-polishing an entire
guitar takes many, many hours even for luthiers
who have had lots of practice.
A French polish finish can be kept in good
condition with occasional restoration, but this takes
professional knowhow. Most guitarists neglect
this until the French polish is worn off down to
bare wood, which then gets dirty and oily, making
restoration much more difficult. Because of
all its drawbacks, I no longer offer French polish as an
option on any part of my guitars. The options
I do offer, however, come really close to the good
points of French polish.
While on the subject of finishes I DON'T use, the
finish system known as catalyzed polymer (there are
several types) bears mention. This material is
a clear plastic that starts as sprayed liquid and
hardens because of an added substance called a
catalyst, which reacts chemically with with the
resin. Catalyzed polymer is virtually the only
type of finish used in guitar factories any more
because it is so labor efficient.
This finish is also very toxic and requires
special equipment and rigorous physical protection
for applicators, including remote-air-supply
breathing masks. Because of its extreme
hardness, it is essentially impervious to abrasive
polishes and therefore cannot be processed
effectively after application. The worst
deficiency of a catalyzed polymer finish, however,
is that it is invariably very thick and must be so
in order to end up level and glossy. Almost
nobody thinks this is a good idea acoustically.
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