In addition, I
use an "open pore" finish process, which leaves
the wood in the most natural condition. The appealing
"warmth" of an open pore oil finish cannot be
duplicated by any surface finish process I know of.
Before I enter into the details
of my method it will be useful to enumerate the general
requirements for producing good instrument-type oil
finish:
1. Careful surface preparation
2. Correct oil of the proper consistency
3. Correct
application technique
4. Careful final polishing
SURFACE PREPARATION
Of all procedures in oil
finishing, surface preparation is the most important. The
reason is clear: in a properly done oil finish the oil is
mostly in the wood, not on it; therefore, the surface of
the wood itself is the primary determinant of the quality
of the finish. Let me emphasize - never start oil
application unless your wood is as flawless as possible -
follow this rule and you will save yourself a lot of
effort.
The sequence I usually use in
surface preparation is as follows:
1. Optional special sanding
2.
Final scraping
3. Normal sanding sequence
4. Wood
polishing sequence
Now I want to point out that
among instrument makers there are both adherents of
"scraping" and adherents of "sanding."
There is a perennial argument over which method is "best."
Since I am naturally a skeptic, I believed no one - I
experimented. My own conclusion at this point is that any
instrument maker who doesn't use both scrapers and
sandpaper is severely limiting his ability to create a
fine finish. Scrapers excel for particular purposes;
sandpaper does what a scraper cannot do. Using both you
can conquer almost any surface preparation problem.
STEP 1.
One of the last operations on a
guitar before finishing is scraping out the binding. It
Is critical that in leveling the binding you don't create
problems that will show up in later finishing. This means
you must pay careful attention to achieving a smooth
continuous contour on the binding surfaces, and must
avoid damaging the soft conifer top. Use a piece of
masking tape on the non-working end of your scraper. When
doing the final flushing of the binding to the top, take
care not to bear down on the scraper or you may "roll
up" the fibers of the top - a nasty defect that will
take a while to scrape or sand out.
The problem I have in scraping
the binding is due to the fact that I like to use solid
flamed wood binding (no white line). While I do avoid the
headaches of white lines, I have to deal with the
pronounced tendency of the scraper to follow the wave of
the grain, resulting In a rippled binding surface. I
counter this effect largely by trying to work the scraper
at many different angles over the binding. In most cases,
this measure alone is not sufficient - in order to
achieve a really smooth contour I have to use 150 or 220
sandpaper adhered directly to a small hard sanding block.
A hard sanding block, used with care, will level this
kind of defect. This is really the only kind of situation
in which I would use sandpaper in contouring, before I
begin my regular finishing sequence. Another place where
you can use this technique is on the sides at the waist.
It is very difficuit to angle the scraper in this problem
area, which is especially prone to rippling. These "special
sanding" operations are what I refer to in step one
above.
STEP 2.
At this point, you can begin
step two, the final scraping operation. Your scraper
should have the finest and sharpest possible burr - stone
the edge and use the burnisher lightly. (Save yourself
some trouble: use a European-made scraper, not a domestic
one.) Scrape from a multiplicity of angles to start, then
gradually shift over to straight over-lapping strokes
with the grain to finish up. To judge the quality of the
surface, continually check the reflected highlight of the
wood, using a light source opposite the guitar. This
method of using highlights to detect defects is
indispensable to proper surface preparation. All common
defects - tear out, ridges, rippling, brace "humps';
etc., can be detected, corrected, and avoided by this
method. Be finicky - the better your scraping, the less
you will have to sand, the more perfect your finish will
be.
I find the scraper is most
useful on the flat or single curved surfaces, top back,
sides, and head. On double curved surfaces, like the neck,
the scraper is less effective for final surfacing. In
these areas, use extra care to eliminate as many ridges
and narrow facets as possible before you finish. The
various curved scrapers are very useful here.
Keep in mind that you may
scrape any direction you wish except dead parallel to the
grain (the edge of the scraper parallel to the grain
direction). Under this condition, a scraper will almost
always tear badly, especially on quarter-sawn wood.
Because a guitar top is
particularly hard to scrape once it Is arched, I usually
scrape to as good a finish as possible while I fabricate
the top (before bracing). In this way, I only need to do
touch-up scraping on the assembled top. Make sure that
you round the corners of your scraper or you are certain
to dent the top. If you have a "clean" dent in
the top, you can often bring it back flush with this
steam method: wet the dent thoroughly with water, place a
damp double thickness of white cotton cloth over the dent;
heat the flat head of a large nail with a flame, then
press the flat face head directly onto the cloth. The
resultant steam will lift the dent, while the cloth
prevents staining of the top.
On the topic of scraping tops -
I have had people tell me, "you can't scrape
softwoods." This is nonsense. You can scrape most
softwoods to a beautiful finish if you sharpen your
scraper to perfection and use the smallest possible burr.
In fact, you can use the scraper with just a clean, sharp,
square edge and no burr at all. Then, while scraping, you
must use fairly light pressure and numerous passes. Don't
ever bear down on the edge or you'll have to start all
over.
STEP 3.
At this point, you will be
ready for the step three sanding sequence. The first task
is to round corners - on the head, fretboard, heel,
binding, and soundhole edge. I use 100 and/or 150 grit
sandpaper folded once or twice on itself. Folding the
paper keeps it stiff, minimizing the danger of scratching
adjacent scraped surfaces. Take your time on this
operation - nicely rounded corners are a premier sign of
fine craftsmanship.
Now you can start sanding the
major surfaces of the instrument. Keep in mind that your
purpose is not to remove lot of material, but rather to
refine the scraped surface, removing scraper marks,
chatter, and other very minor defects. If you have done
your scraping correctly, you should be able to start with
paper no coarser than 220; then you will proceed to 280
and 320. With skill, you can skip the 280.
Most people think of sanding as
something very simple. Actually, sanding is a very subtle
skill that requires patience and experience. To sand
correctly you need the right materials and the right
technique. As for sandpaper, I use no-fill aluminum oxide
or silicon carbide - the highest quality I can buy. For a
sanding block I use an "Artgum" eraser that
measures about 7/8"x 7/8"x 2". I flatten
the bottom of the eraser on sandpaper, and cut little
sheets of sandpaper to fit (about 2"x 2-1/4").
All of the people I have seen
sanding guitars were using big chunky quarter-sheet
sanding blocks. Presumably, they needed a big block to
keep the wood flat. I use a small block, because I have
already scraped the wood flat and smooth, and the little
sanding I do will not change that. Furthermore, by
scraping I have totally circumvented the need for coarse
sanding. For the fine sanding after scraping, I need
sensitivity and control, so I use a small block. The
Artgum eraser is just right in terms of size and hardness.
As for sanding techniques,
there is a common pitfall that should be avoided - the
"back-and-forth" sanding pattern. Virtually
everyone, when given a sanding task, will rub up and back,
end-to-end on the wood keeping the sandpaper in contact
with the wood the whole time. This technique is very poor,
since it resuits in at least twice as much sanding in the
middle as on the ends - often the very ends will barely
be touched at all. To sand evenly, it is necessary to
sand in long separate strokes. Start at one end and glide
the block onto the wood, move forward in a continuous
stroke, and proceed right off the end of the wood. Now
sand the same way on the return stroke. With this
technique you will achieve superior resuits. Of course,
there are many instances in which this exact procedure is
not practical; but even so, try to sand in continuous
discrete strokes.
In general, you will get better
sanding results if you follow these pointers:
1. wipe or vacuum away the
sanding dust between grits 2. use only sharp paper 3. use
the "highlight" method to check for defects
before you proceed to the next grit.
In the past, I have added 400
and 600 papers to my sanding sequence. I am ambivalent
about these grits, because the closed-coat bond does not
work well on wood. These papers clog very easily,
especially on resinous exotics. At this time, I am trying
to eliminate the use of these grits by substituting the
polishing abrasive described below.
STEP 4.
At this point, it would be
possible to begin applying oil; however, to achieve the
best possible finish, I suggest that you proceed to step
four, wood polishing. This method is the newest addition
to my finishing procedure. It is made possible by the
availability of a new product called Micro-mesh, a very
special kind of cushioned abrasive that is capable of
incredibly fine polishing on most any hard surface. Micro-mesh
is so effective that it is possible to polish raw wood to
the point that it appears to already have finish on it.
To be brief, it is the most amazing abrasive product I
have ever used.
Micro-mesh is available from
1500 to 12000 grit, is washable in soap and water, and
wears extremely well. For the subtleties of its use, you
should read the excellent instructions that come with it.
If you stop sanding with 320, you should start with 1500
or 1800 Micro-mesh; after 600 grit paper, you should
start with 2400. You can go clear to 12000 grit if you
wish, but it's a lot of work. My present method is to
finish sanding with 320, then to polish from 1800 using 4/0
steel wool. The steel wool has only one purpose -the
removal of raised grain hairs. Nothing works as well as
steel wool for this purpose. There is only one 4/0 steel
wool on the market that is consistently high in quality -
Elephant Brand. Don't use anything else.
Micro-mesh works best on hard
woods. On mahogany, spruce, cedar and the like I find
that 3200 Micro-mesh is the approximate point of
diminishing returns.
OIL FINISHING
It takes some time to do proper
surface preparation, but lf you do it right, the oil
finishing itself is a breeze. There are many oil finishes
on the market. I have achieved my best results with
polymerized tung oil. I have tried many different brands
of tung oil, and found most of them to be good; however,
I still use the first brand I tried ten years ago, Jasco.
It is readily available (try Standard Brands), consistent
in quality, and reasonably priced.
With respect to the list of
important instrument finish properties already mentioned
above, tung oil scores very high. In addition, tung oil
has very good drying power, and its penetration can be
controlled. This second quality is very important for
instruments, since an oil finish that penetrates deeply
into the wood will almost without exception compromise
tonal quality. For example, I would never use Watco oil
on an instrument. It will penetrate clear through the top,
back, and sides, and it takes two lifetimes to harden. I
have heard guitars finished with Watco -the high
overtones were severely suppressed in most cases. If you
want a "live" guitar, stay away from Watco or
any other thin "penetrating" oil finish.
There are certain distinct
advantages to oil finishes. They tend not to show surface
defects (nail marks on the top, for example), and they
are easy to repair. (An oil finish repair has two steps -
burnish the defect with 4/0 steel wool, then apply oil
and wipe off the excess.) Finally, players like oil
finished necks because they are "fast" - never
"sticky" like a surface finished neck.
Now let's delve into oiling the
guitar.
At this point, you need to
decide whether you want to glue the bridge on the
unfinished top, or wait till after finishing, in which
case you will need to scrape away the oil where the
bridge will glue. I have tried both approaches and
conclude that neither method is decidedly superior. All
in all, I prefer gluing the bridge on the raw top,
because I don't like to get glue and water all over an
oiled guitar top. (My bridges are finished with tung oil
while still attached to the work block).
Now proceed to put on the first
coat of tung oil. Filter the oil into a shallow container
and use a white cotton or linen pad for application.
Start with the top (to avoid possible color transfer from
the back and sides), and apply the oil quickly to one
quarter of the top - no more. Now immediately wipe off
the excess oil with a white cotton rag (cheesecloth is
good). Do not use a synthetic fiber rag; it will scratch
the wood.
Proceed to finish the rest of
the top, one quarter at a time, wiping off the oil
immediately after application. Do not let the oil soak,
and certainly do not thin down the oil before applying it
- use it as it comes from the can. You want minimum
penetration to avoid compromising tonal response.
Furthermore, do not try to leave any oil on the surface,
on this coat or any other coat; wipe off all the excess.
If you try to build tung oil on the surface, you will
regret it later when you are rubbing out.
It is very important to apply
oil to small sections, wiping it off quickly; otherwise,
you will not achieve an "open pore" finish on
the porous woods. If you wait too long to wipe off the
oil, it will thicken and not "wick" out of the
pores into the rag; as a result, after repeated coats,
the pores will be glossy, which looks bad on an open pore
finish.
Continue with the above method
over the whole instrument, including the fretboard. Do
the neck last, so you can use it as a handle while oiling.
Hang the guitar to dry.
While oiling, use some sort of
white cotton glove on the hand you hold the guitar with (I
use a cotton sock). Do not touch the guitar with your
bare hands at any time during the finishing process.
Until its completion, a tung oil finish may take
fingerprint stains, especially on rosewood.
Each coat of tung oil should
dry about one day. Rub gently between coats with 4/0
steel wool to remove any raised grain or surface debris.
If the tung oil seems sticky when you start rubbing, stop
immediately; otherwise, you will end up with a mixture of
tung oil/steel wool "goo" in the pores. Let
tung oil dry thoroughly before steel wooling.
If your surface preparation was
good, you should have an attractive finish on most any
hardwood after three coats. In order to maintain open
pores, you should probably not apply more than four coats.
On non-porous woods, five or six coats are fine.
You will probably not be
satisfied with the sheen of the top after three coats. I
have found that cedar and spruce are relatively difficult
to oil finish. I often apply up to eight coats on the top
to achieve a satisfactory sheen. This number of coats has
very little effect on tone as long as you do not try to
build a finish on the surface of the wood. Remember, wipe
off all excess oil on every coat. In the process of
gluing a bridge onto a finished cedar top, I have had an
opportunity to examine the result of eight coats of tung
oil, properly applied. I estimate that the total
thickness is "003 - .005". Of course, much of
this "thickness" is really penetration; the
total amount of oil on the guitar top is actually very
small. The result, I find, is a practically negligible
effect on tonal response.
One more pointer in finishing
the top - do not under any condition use heavy pressure
when using steel wool; it is more abrasive than you might
imagine, and can easily rub right through the beautiful
sheen on your top.
When you have applied your last
coat of oil, it is important that you wait for the entire
finish to harden before attempting the final polishing. I
would consider one week to be a minimum; four weeks would
be ideal.
POLISHING
The polishing process is
relatively easy. Go over the guitar carefully and gently
with 4/0 wool - use light pressure for a burnishing
action. If you run across any "beads" of tung
oil, which sometimes form at the pores, do not attempt to
remove them with the wool. Instead, take a brand new
single edge razor blade and lightly scrape over the beads
(at a negative rake) to remove them. Then continue with
the wool. Be especially careful on all corners.
If you wish, you can polish
further using Micro-mesh. This will work only if the oil
is thoroughly dry. Start with 6000, then go to 8000 and
12000, all the while using fairly light pressure. Wipe
the surface between grits.
When you are done with
polishing, apply a coat of lemon oil treatment (I use
Jasco) to all finished surfaces, using a white cotton pad,
and let dry. This step Is important as it will satiate
the surface's affinity for oil, and prevent finger-printing.
Finally, polish the whole guitar with thoroughly cleaned
burlap.
To care for the finish, use
burlap for cleaning and polishing. A damp rag may be used
on stubborn residue; wipe dry immediately. I have found
that regular use of lemon oil treatment is really not
essential to the longevity of the finish. A yearly
application should be sufficient.
Personally, I recommend against
the use of waxes, since I believe wax will slowly degrade
a finish, whether oil or surface finish. In particular,
wax application will ruin an open pore finish. Waxes are
popular because they yield a fast, easy surface sheen. If
you do a careful job in finishing, however, you will
achieve a permanent sheen with the tung oil alone which
totally obviates any need for wax.
When using tung oil for
finishing, there are a few things to remember. First,
tung oil has very good drying power, which means it will
eventually gel in its container. Therefore, buy only pint
containers and immediately transfer the oil to flexible
plastic containers from which all air can be expelled
before sealing (hiker's food tubes or photographic
chemical "accordion" bottles work well). Then
store the tung oil where it will not be exposed to light.
Partially thickened tung oil can be salvaged by thinning
with mineral spirits; but never use such oil on an
instrument. Only fresh oil should be used for fine
polishing.
With one exception, tung oil
will dry on any wood I have worked with (which is unusual
for an oil finish). I have never figured out how to tell
the "non-oil" cocobolo from the "oil"
cocobolo. On the "non-oil" variety, tung oil
will remain tacky indefinitely (you can clean off the oil
with mineral spirits). Fortunately, most cocobolo can be
left unfinished but this would be unwise on an instrument.
On anything but an instrument, I would just apply a
"color coat" of tung oil, and rub off any
slight stickiness with steel wool. For an instrument, I
would experiment with a very fast-drying lacquer or
shellac in light coats. On some cocobolo, however, even
most lacquers will not dry.
I have recently been
experimenting with an oil finish called Tru-Oil, which is
intended for gun stock finishing. I do not know the
contents of this product, but it strikes me as being a
"bodied" oil finish, that is, an oil/resin mix.
With respect to build and drying power, it seems superior
to tung oil, and probably has better moisture resistance,
too. In addition, it works very well on cedar. Before
using Tru-OiI on an instrument, I intend to check into
the resin content. I suspect it contains urethane, which
has a reputation for compromising tonal response. Like
tung oil, Tru-OiI will not dry on certain cocobolos.
I have also recently tried
samples of 3M's Scotchbrite Cleaning and Finishing sheets.
The Ultra Fine Type S (Grey) may replace 4/0 steel wool
for many purposes, and the Cleaning and Polishing Type T
(white) looks good for satin polishing.
Wishing all success in oil
finish, I believe if you follow my methods you will be
very pleased with the results.
Postscript: I no longer use
steel wool for finishing. 3M's Scotch-B rite Cleaning and
Finishing Sheet, Ultra Fine Type S (grey), is very
effective for both final wood surfacing and rubbing
between coats. Also, the Cleaning and Polishing Type T (white)
can be used to advantage in some situations. The Ultra
Fine can often be found in hardware stores. Both grades
can be obtained through industrial suppliers. Having now
finished a guitar with Tru-Oil, I can say that it is
superior to tung oil for purposes of my method. It dries
and builds faster, has better moisture resistance, and
can be padded onto cedar to get a faster build. Finally,
it seems to have no detrimental effect on tone. By the
way, if you want to make your own lemon oil treatment,
try 60 drops of lemon grass oil (from a health food store)
In 50 milliliters of odorless mineral spirits (paint
thinner). I'm experimenting with this mixture with good
results.
Bill Woods is a classic
guitarmaker, tool designer, and consultant from Prescoff,
AZ. Bill has been a big help to us over the years with R&D
and has several items that we carry in this catalog to
his credit.
SUPPLIERS
Micro-mesh is sold by Micro-Surface
Finishing Products, Inc., 1217W. 3rd Street, Box 818,
Wilton, Iowa 52778. It may also be available from a local
vendor. Check with aircraft maintenance suppliers.
Jasco Tung Oil and Lemon Oil
Treatment are made by Jasco Chemical Corp., Mountain View,
CA 94042.
Tru-Oil is normally obtainable
through gun shops, and is made by Birchwood Casey, Eden
Prairie, Minnesota 55344. Santa Cruz Guitar, carved maple
back, flat top.
SAND PAPER
On the backing of most
sandpapers you'll find the following information:
1. Type of abrasive: garnet,
aluminum oxide, flint, silicon carbide, emery. 2. The
weight of the paper: A, C, D, and E. 3. Whether it's open
or closed coat. 4. The grit number (120, 240, etc.), or
the grit symbol (expressed in aughts such as 6/0, 2/0, 8/0,
etc.).
Most luthiers know that
progressively finer grits are used on the work as it
approaches finishing, but not all luthiers know how to
use these other features to their best advantage.
Following Is a brief discussion of these lesser known
features:
ABRASIVE TYPE
To refer to number 1, above -
Garnet is popular among cabinet makers and furniture
builders, partly because it's been around for many years,
but largely because of its crystalline nature. As it
wears it fractures into smaller grit with similarly sharp
cutting edges and it cuts wood through a scraping rather
than a scratching action. It's also a relatively
inexpensive sandpaper.
Aluminum oxide is a hard,
durable, more expensive abrasive, which is good for high
speed sanding of hardwoods. Because the grit has less
chip clearance it has a tendency to load when abrading
resinous woods and soft woods. In our own use, we have
found that spraying silicone on our thickness sander belt
prior to sanding resinous woods such as Indian rosewood,
more than doubles the belt's life.
Flint is the original sandpaper
and though it is not very tough and wears quickly it is
useful for removing substances which would simply clog a
more expensive sandpaper. Use flint for removing paint,
resins, sealers, etc.
Silicon carbide is considered
by many to be the best all around paper. It's available
in either waterproof black, or white paper. It's the
hardest of the abrasives, though aluminum oxide, garnet
and emery all have a greater resistance to wear. Silicon
carbide paper does not load quickly because of the grits'
greater chip clearance angles, but it does break down
quickly on hard metals. It's a good paper for everything
else, though, from softwoods and hardwoods to varnish,
lacquer and other finishes.
Emery paper has the greatest
resistance to wear of all the abrasives listed, but
because of the grits low chip clearance angles and its
tendency to fracture into dull cutting edges, it promotes
heating. It is therefore best used with a lubricant and
generally on metals only.
WEIGHT
The weight symbols on the
backing: A, C, D, and E corre- spond to the heaviness and
the flexibility of the paper. (Cloth and fiber backings
and combinations thereof are more for heavy duty purposes.
"J" weight Is a relatively light weight paper
and is somewhat flexible and "X" weight is a
heavier weight and virtually Inflexible). "A"
weight is for finishing. It's very light so that you can
feel surface defects and it is flexible enough to allow
sanding in small, narrow areas. "C" and "D"
weights are heavier and carry coarser grit. These papers
are not as flexible but can handle more pressure and are
used with orbital or in-line sanders as well as in hand
sanding. "E" weight is the heaviest of the
papers and is found in roll form for use with belt, drum
and thickness sanders.
OPEN & CLOSED COAT
"Open coat" paper is
paper in which the grit doesn't entirely cover the paper's
surface. Generally about 50% or 60% of the surface is
covered by grit. Its best use is found in sanding (with
light pressure) resinous woods, or other woods that have
a tendency to clog. Not only do the open spaces of "open
coat" paper resist loading but they permit you to
flex the paper more easily when sanding Irregular
surfaces.
"Closed coat" papers
are completely covered with grit. It's best to use them
on hardwoods or woods that don't clog the paper. They'll
produce a smoother surface and will last longer, even
under heavy pressure.
GRIT NUMBER
Some manufacturers refer to
their papers by grit number, others by grit symbols (aughts)
and still others by the rather arbitrary system of coarse,
fine, finer, finest, most finest, super most finest, ad
infinitum. The fine abrasive, grit #400 corresponds to 10/0,
#320 to 9/0, #80 to 1/0 and so forth. The grit number is
determined by the openings per square inch in the screen
mesh through which the grit is sorted. #80 grit paper,
for instance, carries grit that has fallen through a mesh
with 6400 openings per square inch (80 X 80).
Remember not to go from a
coarse paper to a fine paper. Use a medium grit paper in
between, otherwise the deeper scratches left by the
coarse paper will be very difficult, as well as time
consuming to remove.
After final sanding it's a good
idea to begin finishing the work at once. The raw wood
can pick up moisture and dirt from the air, or the wood
could be bruised by a nonchalant, bull-in-a-china-shop
type person. So protect your work and finish it upon the
final sanding!
FINISHING
Finishing is important for
keeping dirt out of the wood, for bringing out colors and
visual and tactile qualities, for preventing surface
damage from heat and abrasion, and for keeping moisture
exchange with the air to a minimum. But finishing is also
important to the instrument builder as the choice of
finishing materials can greatly influence the clarity,
brilliance, and volume of the instrument.
Possibly a gap in our finishing
section is the absence of a good varnish for guitar and
dulcimer makers. We can readily obtain spirit and oil
varnishes but these are primarily for violin makers, and
are available through violin supply houses. The varnish
that we had carried is no longer produced, and we were
unable to find anything that would have been a suitable
substitute. However, it was a tung oil based varnish that
worked by polymerization, much like that described in
Bill Wood's article, Fine Oil Finishes for the Instrument
Builder. It is our suggestion that you give Bill's method
a try. It will undoubtedly yield first class results.
LACQUER
For about two years we carried
the Sherwin Williams lacquer which was a special
formulation for the C.F. Martin Company. This was a
pretty good lacquer but if sprayed any thicker than 6
mils it would develop cracks. This was more often a
problem only around the neck. (Martin sprayed their
guitar bodies sans neck.) After two years of experience
with this lacquer, we concluded that the whole trick to
the Martin finishing system was carrying out their entire
process. This involved special vinyl undercoats, sealers,
and retarders which were just too many chemicals for us
to stock. There seemed more than occasional blushing
problems with the Sherwin-Williams lacquer, too.
In the last several years we've
carried a lacquer, which, if we were to judge only from
its sales, is an excellent lacquer. We are now selling it
to several customers In 5 gallon pails. One of the men
here, who builds and repairs says it's the best lacquer
he's used since a German lacquer became obtainable about
12 years ago. Charles Fox, (see article on Universal Wood
Bending Machine) who headed the School of Guitar Research
and Design for many years, and who has had considerable
experience with finishes and their attendant problems,
had nothing but rave reviews for this finest of lacquers.
USE OF LACQUER
Our FL lacquer is a very hard
lacquer, and will polish to a high gloss. We've heard no
complaints about cold-checking, but with such a hard
lacquer this should be a consideration in colder climates
(where if your instrument is exposed to extreme cold the
finish will shrink but the wood won't, leaving you with a
cracked surface). If you find it too hard for your
purposes, 1 oz. of zinc stearate per gallon of lacquer
should soften it adequately.
If all the preparation work has
been completed (see Bill Wood's article on Fine Oil
Finishing) and you are ready to finish your instrument we
offer a few guidelines: Our thinner, FLT should be used.
This thinner was formulated to be used with our lacquer;
should you use other thinners you can expect drying and
flowing problems, and you can expect rub-out time to
increase, too. Use other thinners to clean the gun if
they are cheaper.
There is much written on the
subject of spray lacquering, and there are as many
methods for finishing an instrument as there are
instruments (well, almost). The following method has been
used most successfully:
1. Wash coat all surfaces with
a smooth, wet coat but not wet enough to run.(Thin
lacquer approx. 25% lacquer to 75% thinner.) On resinous
woods, such as Indian rosewood, you might want to spray
on two light coats of shellac, no more than a two pound
cut (2 pounds shellac to 1 gallon of alcohol).
2. Scuff-sand lightly with #320
paper to remove "hair."
3. Fill all porous wood with
either our FT, transparent fill, by squeegeeing it on
with stiff cardboard, or with a pore filler of your
choice.
4. Sealcoat just as you did the
washcoat. Color (our FS alcohol stains) may be added to
the lacquer at this time, if desired. (The final few
topcoats should be clear lacquer.) Remember to remove the
shine from unfilled surfaces. Spray as many sealcoats as
necessary until a uniform matte surface is achieved
without sanding through to wood. The purpose at this
point is to get the surface flat. This may take as few as
two coats and as many as 10 coats depending on prior
surface preparation. These can be sprayed at about one to
two hour intervals with no more than four coats sprayed
in a 24 hour period. (The solvent needs to be allowed
time to thoroughly escape.)
5. Body the finish by spraying
wet coats each hour in a warm, dry place. Find the
mixture ratio that suits your gun the best. This depends
on air pressure, temperature, and number of coats to be
applied. (One of the men here sprays full strength, but
he has an air compressor.) Sand the final coat or the one
before the final coat with #600 wet/dry. Use a lubricant
(soapy water or kerosene) and a rubber block. If you are
spraying in an area of high humidity, you might encounter
blushing (a milky haze) in the finish. You can relieve
this problem by spraying on a light coat of straight
thinner.
6. Finally, after one more day
(preferably more) to dry, rub the finish out with our
abrasive cut polish, FCP, and if you want a really glossy
finish use our FFP fine polish. If you want a really-really,
glossy-glossy finish, then follow the FFP with our FSP
super fine polish/cleaner. If after polishing you find
that your instrument needs to be resprayed you can remove
the polish with dilute alcohol (with water).
USE OF THE SPRAY GUN
1. Check the gun for break-up.
Hold it up between a light and yourself to see if the
fluid is misting when it's a foot from the nozzle tip. If
not, clean the tip with a wooden splinter or solvent or
both. Screw the tip on very tightly and make sure that it
seals. If it leaks behind the cap (tip) then remove it
and clear the cap's seal at the end of the spinner. If it
still won't break up, then the finish is probably too
thick.
2. Spray in a smooth motion,
overlapping 50% with the last stroke. Place a light so
you can see the shine of the finish going on. It should
be thick enough to run together but not heavy enough to
run. If the gun is not held closely enough to the surface
or if the air pressure is too high you will encounter
overspray. The lacquer will dry on contact and will not
be absorbed by the surface which will look rough and
gritty. If you spray too closely, you will encounter sags,
bubbles, orange peel and the like.
3. Always start the spray
pattern with the gun pointed off the work, then bring it
past the work smoothly, then back on, half a spray-width
lower, etc., until you've covered the whole surface.
Text From The Luthiers'
Mercantile Catalog - 1993
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