THE PROCESS IN
GENERAL
Porous woods must be filled: In
F.P. it can be done either with pastewood filler, our
transparent filler (FT) or by the old "Pumice in the
F.P." method. Instructions for the use of pastewood
filler will not be included here except to say that a
good wash coat of shellac should precede the use of
pastewood filler to help color the pores dark, not to
stain the wood. After filling and touching up the surface
lightly with #400 sandpaper to smooth it and even the
color, F.P. can begin. The original wash coat can be put
on either with a brush or with a well soaked pad. The
wash coat should dry in a few hours. The filler (if not
using our FT) needs 48 hours if possible, or even more.
24 hours in a warm room is absolute minimum.
Another way to fill porous wood
is to begin the wash coat with a well soaked pad.
Continue laying on wash coats of F.P. until a slight
surface begins to appear - a shine. Then sprinkle finely
ground pumice powder over the surface a little at a time
and with circular motions begin to work it, along with F.P.,
into the pores. In skilled hands this is a quick and
effectIve way to fill porous wood.
From this point on the balance
of the filling can be done by the F.P. itself since,
unlike other finishes, it has the characteristic of
filling small holes.
The finish is now ready for
bodying. That is to say, building up a layer of F.P. of
adequate thickness. This is done by going over the
surface 100's or 1000's of times in circular or "figure
8" motions, leaving endless coats of minute
thickness which eventually add together to make a full
depth surface.
Where adequate depth has been
achieved, a difficult part remains - spiriting off the
surface. In this process, a nearly dry pad is used with
considerable pressure and speed (often in straight lines
slightly moistened with thinner) to remove any oil from
the finish that was used during the bodying. The intent
is to glaze the surface and produce a shine.
So the steps are as follows:
1. Seal with a wash coat
2. Fill porous woods
3. Body the finish
4. Spirit off the surface
THE PROCESS IN DETAIL
The Pad, "Fad" or
"Rubber": The pad should
be made from a fine, soft, lint-free material, like linen,
unbleached cotton, etc. Make sure you wash this "trace
cloth" several times to remove any hint of lint. Do
not bleach it, as this weakens fibers. For guitars, a
piece about 4"-8" square is O.K. When one area
wears out, move the stuffing material over a bit.
The best stuffing material
seems to be cotton waste. The cotton waste we supply is
superior to other materials in that it doesn't tend to
compress and harden during the polishing (as does cotton
batting). Use enough to make a hard-pressed ball about
the size of an egg. Wrap the stuffing with the cloth and
pull all the sides into your hand to stretch the cloth
over the stuffing. When you need a point, take one end of
the pad and squeeze it out to form a point, then press it
onto the work with your first finger. (Another suggestion:
one of our local customers, is an old hand at French
polishing; he uses foam rubber inside the cloth - a
slight squeeze pushes out the polish; less pressure soaks
it quickly back into the pad for immediate control.)
The Polish:
Generally, about 10 oz., of our French polish thinner (FFPT),
which is a high grade ethyl alcohol, will dilute 1 oz. by
weight (2 oz. by volume) of our shellac. The remaining
thinner can be used for spiriting off, thinning the pad
mixture, pouring into the pad, keeping some in a bottle
to keep the pad wet, etc.
Measure out small portions of
the shellac and thinner as you need them and keep both
the thinner and the F.P. tightly capped - they are
deliquescent and draw water from the air. The mixed F.P.
has a shelf life of about 9 months at the most. The
dilution can vary considerably, but the ratio of 10 fluid
ounces to 1 ounce by weight of shellac is recommended.
For measuring out the proper dilutions, use a simple
kitchen measuring cup, a chemists burette or pipette,
level shovelsfull or whatever; the more accurate, the
better control you will have. For mixing, any clean jar
with a tight fitting lid will do, although smaller is
better. For storing mixed shellac, minimal air space
above the solution is best. Be sure the lid you use is
unwaxed, as the thinner will dissolve the wax. Turn the
jar over once or twice during the day. It should dissolve
easily overnight. For polishing, keep it in a small, 4 oz.
squirt bottle.
BEGINNING ON FILLED OR NON-POROUS
WOOD:
Load the pad with polish from
the squirt bottle until it leaves a good, wet streak on
dry wood. Then, tap it hard into your palm to disperse
the F.P. and to flatten the pad. Keeping the pad very
tightly held and the wrist stiff, lay on long, straight
strokes, one after another, covering the whole surface
until the surface is wet. In a few minutes the process
can be repeated, and so on until the finish begins to
"build" (shine). The pad is now dry at this
point. Use small, circular motions which drag a little
but not too much. About 2"-4" diameter circles,
working gradually around and over the whole surface seem
to work the best. The pad must never stop on the surface
- it is lifted off and put on while still in motion. This
is an absolute rule and must become a habit. The circular
strokes are the fastest builders, but vary them with long,
narrow "figure-8" strokes which reach right
across the edge of the instrument.
Sticking vs. Building:
If you keep the pad too wet with polish, it will pull up
and melt what you have laid down previously. If you keep
it too dry, you will rub without building. The pad should
leave a smear that dries almost when it is laid down. The
movements should be quick and light when the pad is a
little wet, slower and heavier when it is drier. In order
to avoid sticking, a small amount of fine mineral oil,
poppyseed oil, linseed oil or other light oil can be used
as a lubricant. This must be kept to a minimum as it
tends to soften the final polish and can be nearly
impossible to remove. You can use fine mineral oil,
spreading a drop over a fairly wide area of the work.
"Recharge" the pad by
squirting polish directly onto the surface then, tapping
it into the palm of the hand. The cloth over the pad must
be kept tight and a tight grip must be kept on the whole
pad.
Difficuit Areas:
Guitars are usually polished before the bridge is put on.
The bridge area is marked (just a hair inside the actual
bridge size) after the polish has dried and then scraped
clean of polish with a chisel. Then the bridge is glued
on.
The really difficult area is
where the top meets the side of the fingerboard. The only
solution to this problem is to make sure that every time
you pass that area, you polish it with the point of the
rubber in circular and straight back and forth motions.
Otherwise, it will build more slowly than other areas and
appear streaked and pale.
Rough Surface:
Sometimes you will use too wet a pad and while not really
pulling up the finish, it will leave the finish in a way
that is hard to remove. Give the polish at least a few
hours to dry, and then with #600 wet/dry paper, a rubber
block and some coal oil (kerosene) for lubricant, you
very carefully sand the surface smooth. You can then
begin to polish again on a smooth surface.
Spraying French Polish:
You may spray F.P. It's a great time saver. Since no oil
is used, quite a hard smooth body can be produced very
quickly. It's also nice for areas like the machine head
slots, which are hard to reach.
Staining:
With the two packets of shellac we supply, you may
achieve a range of color by mixing the amber with the
blond and still retain good transparency. If it is put on
at an even thickness, the color will be even. If you
desire to darken the color, about halfway through the
bodying process, you can add liquid stain directly to the
polish in small amounts. Keep the colored surface even
and do not apply color to a rough surface that is to be
smoothed out later.
Drying:
Usually at one or two points during polishing, the
surface becomes rather thick and tacky. These are
dangerous points but they also allow you to move the
polish around to fill holes, etc. to the greatest extent.
It is best to put the instrument aside for 2 or 3 (or
more) hours to let the finish set before going on.
Spiriting Off:
This is the most difficult part of French polishing and
may require some practice. As you finish the last stages
of the bodying process, begin to add thinner instead of F.P.
to your pad and work without oil. Keep the pad dry and
rub fairly fast and press hard. This will usually, in
time, bring up a shine and remove the oil that has been
used in bodying. The high pressure tends to compress the
finish and force out the oil while glazing the surface.
Another Method:
For those who do not F.P. enough to keep in practice, the
final surfacing or glazing can be done very nicely with
our FSP polish. Let the finish dry completely (a couple
of days, if possible) then, with terrycloth or some soft
cotton, rub the surface very hard with FSP until a
perfect shine comes up. You might prefer this rather
softer shine to the brilliance of a spirited off glaze.
Some Points to Remember:
F.P. is an art and an acquired skill. It takes some time
to learn, so don't give up with your first try. The more
you practice, the better you'll become.
The best materials are a must.
Shellac comes in all qualities from garbage to gold. The
best is easier to build and to spirit off. It lasts and
wears much longer, and produces a more beautIful and
transparent finish.
TECHNICAL TERMS
Cold-Checking:
Fine cracks that often run like spiderwebs through the
finish. They are caused by sudden changes In temperature
in a finish not elastic enough, or, which does not expand
and contract at a similar rate to wood. Or, the finish
simply may not be tough enough. Old lacquer finishes
nearly always show evidence of cold-checking. The
elasticizers have dried up and the finish becomes too
brittle to resist temperature changes.
Wash Coat:
A thinned or fairly fluid coat of finish put on the raw
wood, usually to seal it, reduce its absorbency and to
provide a wood-penetrating base for the later coats.
Pad: A
pad ("fad" or "rubber") is a cloth
surrounding some absorbent material and used, one might
say, as a dryish swab to apply finish.
Text From The Luthiers' Mercantile
Catalog - 1993
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