From: sjbarry@ucdavis.edu (Sean Barry)
Newsgroups: rec.music.makers.acoustic
Subject: Pearl Inlay Technique
Date: 30 Oct 1995 21:02:44 GMT
Pearl Inlay
Sean J. Barry
Davis, California
This is a three-part discussion about the practice of stringed
instrument inlay. Part I covers the principal materials and tools, Part II
covers pearl cutting and layout techniques, and Part III covers inlaying
technique. The usual disclaimers apply--I recommend specific brands
only when either no other will work or I have no experience with
others. As far as I know, no manufacturers mentioned here have ever heard
of me.
Your feedback is solicited and welcome. Feel free to download the
text for personal use, but otherwise please do not crosspost, forward,
or reproduce the text without permission.
I. Materials and tools
Any number of flat or flattenable materials can be inlaid into the
surfaces of instruments, furniture, foreheads, etc., but the most popular
for stringed instruments has always been mother of pearl from pearl
oysters and a similarly-derived material from abalone shells. Mother of
pearl (nacre) is the material which composes the pearl oyster (_Pinctada_
species) shell, although normally the term refers only to the interior
lining of the shell. All shelled molluscs possess a shell lining that
resembles mother of pearl, but those of the pearl oyster and
abalone are especially attractive and the shells are large enough to yield
reasonably large flat pearl blanks. Oyster mother of pearl is usually
white or gold, with red, blue, and green irridescence and often with
swirl, "eyes," a curly pattern, or other figure that results from
proximity to the hinge or from imperfections or worm borings in the outer
shell. Pearl oysters are native to the warmer parts of the Pacific and
Indian Oceans, from the Gulf of California to the Red Sea, and are
"farmed" in Asia for the cultured pearl industry. I don't know if they
are also used for food. I also don't know what, if any, percentage of the
pearl oyster shells that are imported for inlay pearl originate in
cultured oyster beds, but I hope it's large. Abalone (several
_Haliotis_ species, of which red and green abalone are the most popular
for inlay) is confined to coldwater parts of the Pacific Ocean, and
doesn't occur in the Indian Ocean. Abalone for inlay originates
completely from "wild" specimens harvested for their meat, which is
considered an ultimate seafood delicacy. Some abalone is now being
farmed, and perhaps in the future most of the commercial material for food
and shell will originate from such sources. Other materials occasionally
or commonly used for instrument inlay include bone, ivory, tortoise shell,
silver, gold, brass, nickel silver, and various woods and plastics
("mother of toilet seat"). Each has its own peculiarities, but the
process for cutting and inlaying all such materials is basically the same.
Several steps are entailed in converting an arched shell to flat pieces
for inlay blanks. The first is to mark the shell (on the inside) to take
best advantage of the figure and pattern, and to minimize the arch in any
particular rough piece (the less arch, the larger and thicker the final
blank). The resulting jigsaw puzzle is then bandsawn into arched
individual pieces that are lined with mother of pearl on one side and with
the shell exterior on the other. The rough exterior surface is then
ground off to reveal the underlying mother of pearl. The resulting piece
is anywhere from <1mm to 25mm thick (up to 1" for really thick shells at
the lip), and it is still arched. Chuck Erickson, the man who taught me
how to do inlay, had two large double-wheel enclosed grinders for
flattening the blanks, and they did this job efficiently and well. I
expect that other blank suppliers have similar equipment, because it is
heavily tedious to flatten blanks against a normal grinding wheel, and the
resulting product is vewry inconsistent. The amount of handwork that goes
into planning, marking, bandsawing, and preliminary grinding renders the
blanks rather expensive, especially for smaller, more difficult material,
such as green abalone. Also, at least one pearl supplier that I know of
has been so overexposed to the fine dust that results from grinding the
shell that he has been seriously ill with silicosis, a potentially fatal
lung disease--if you grind shell or cut lots of inlay, wear an
OSHA-approved respirator. The finished blanks are characteristically
about 1.5-3mm thick. Some suppliers furnish two thicknesses--the thin one
for inlaying flat surfaces, and the thick one for arched fingerboards.
Blanks may be sold by the piece or by weight--thin blanks when sold by
weight are usually more expensive because per unit weight more work is
involved (there are more blanks).
The tools necessary for cutting and inlaying pearl include good lighting,
a jeweler's saw, a homemade cutting jig, a scribe (with a sharp metal
point that is hard and stiff enough to scribe very hard wood), a few
needle and small mill files, a Dremel Moto-tool (or similar high-speed
drill) with a Dremel router base, various bits and appropriate collets for
the Dremel, a jig or vise to hold the object to be inlayed, and a 2.5" x
5" or similar rubber sanding block. For lighting, use a Ledu or similar
swing-arm lamp (some prefer fluorescents). The jeweler's saw resembles a
coping saw with a very slender blade, and they and the blades are
available from lutherie and lapidary suppliers. Blades are typically
graded as "fine," "medium," and "coarse," but the actual thickness varies
among suppliers, because dozens of thicknesses are available from the
manufacturers. I use "medium" blades for most of my work because they are
less subject to breakage than fine blades and less likely to bind and
break the inlay sheet than coarse blades. Fine blades are usually
recommended for scrollwork and other intricate inlays, but as your skill
increases you will have less occasion to use them. Beginners should
purchase at least 2-3 dozen blades. Many inlay artisans use a jeweler's
saw with an adjustable throat to accomodate variations in supplied blade
length. Such an adjustment feature also permits the use of broken blades,
but in my experience this is a waste of time unless the blade was broken
before it was ever used. The homemade cutting jig consists of a long
piece of wood (preferably hardwood, such as maple or birch) about 12" x 3"
x 3/4" with a narrow slot through the middle and a 1/2" or 3/4" hole at
the end of the slot:
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The jig is C-clamped flat to a table so that the slot and hole extend
beyond the edge, the pearl sheet is positioned over the hole, and the wood
supports the sheet while the saw cuts downward. The scribe is used to
inscribe the exact shape of the inlay into the wood that will be routed
for the inlay. Many hardware stores sell utility scribes--the one I use
consists of knurled steel shaft with a fairly fine hardened steel point
that is removable with pliers--spare points are stored at the opposite end
of the scribe, which is sealed with a hexagonal plastic cap. A small mill
or needle file may be handy for removing the small spur that sometimes
remains at the end of the blade path, but otherwise its use is rather
limited. Do not rely on a file to clean up roughly-sawn inlay, as the
pearl is quite hard and is not easily filed. Just holding an inlay for
filing invites breakage.
The Dremel moto-tool, which is one of the most useful of all tools for
general lutherie, is used to delineate and rout the inlay pockets in the
wood. Economy on the Dremel is false: buy a variable speed, ball-bearing
model, and if you can afford it, buy two. Three is not too many.
Numerous bits, sanders, cutting wheels, buffers, etc. are available, but I
have found that just 2-3 bits are necessary for inlay. These include a
fine-pointed bit, a bit with a plain shaft that ends in a tiny cutting
ball that is slightly larger in diameter than the shaft, and a fairly
large (1/16" is good) router or downcut bit. The pointed bit is used in
the tool freehand to cut down the edge of the inlay pocket, the ball-end
bit is used on the tool in a router base to undercut the edge after the
pocket is delineated deeply, and the router bit is used (also in the
router base) to hog out waste wood in the middle of the pocket and to even
up the pocket depth. All three bits are offered by Dremel, but I have
found that their pointed bits and ball-end bits are generally too large
for inlay work. I use dental bits that I obtained for free from my
dentist--used bits are entirely sharp enough for inlay, and will remain
sharp for a long time. Quite a variety of dental bits is available, from
exceptionally finely-pointed carbide bits to tiny ball- and cone-shaped
carbides and various straight and pointed diamond bits. One request to my
dentist and a 30-day wait yielded a lifetime supply, even if I live a
really long time. You will still need the router bit(s), and you will
need one or more Dremel collets to match the dental bits. Dremel's router
bits (as far as I know) are not carbide--they do produce some
carbide-coated general cutting bits, but I have not been satisfied with
way they cut ebony and especially rosewood. However, various lutherie
suppliers stock very satisfactory carbide downcut and router bits with
1/8" shanks to fit the standard Dremel collet, and I happily use these for
the rough work. Stewart-Macdonald and perhaps others (standard
disclaimers) have various plexiglas router bases available for Dremels,
but it is pretty easy to make your own from 1/8" Plexiglas or (as I
recommend) 1/8" polycarbonate (Lexan). I don't use clear bases for inlay,
but I do for some other lutherie operations. You can use a padded wood or
metal-working vise to hold the object that you are inlaying (usually a
fingerboard or peghead already attached to a neck), or you can build a jig
to hold it on a tabletop--either way is fine. Purchase a standard rubber
sanding block from the hardware store, along with lots of 80, 100-120,
220, 320, 400, and 600 grit open-coat and wet or dry sandpaper--a large
mill file is handy also. Other tools you might need include a very small
chisel for cleaning inlay pocket corners, various gravers if you intend to
engrave the pearl, and other bits for the Dremel as the need arises.
II. Inlay patterns, layout, and pearl cutting
When last we met we spoke of tools and materials, and I left you staring
at an array of scribes, jeweler's saws, thin blades, and noisy high speed
drills. Now, you must choose an instrument or other object to be inlaid,
purchase some inlay material, and either purchase or design a pattern to
cut. For your first effort, I suggest that you stay with mother of pearl
from the pearl oyster, and save abalone for a later endeavor. The reason
is simply that abalone tends to be somewhat more brittle, and full of
fragile natural laminations (the black lines that help to make it so
attractive). If you insist on abalone for your first inlay job, use red
rather than green abalone because red is less fragile (and less
interesting) and generally comes in larger, more easily handled slabs--the
shells are larger. I have seen pearl advertised in thicknesses that range
from 0.02 to 0.06 inches. Use material that is 0.02--0.04" for flat
surfaces, and thicker material for curved surfaces, such as arched guitar
fingerboards. Thick slabs are also less likely to break as they are cut.
Thick slabs do cause a higher rate of blade breakage, so be sure to have
an ample stock of medium blades available. Pearl is sold by the piece or
by unit weight, typically by the ounce. Many suppliers claim that one
ounce is sufficient to cut a Gibson-style banjo neck, but I have found
that it will cut all of the fingerboard pieces but not usually the peghead
pieces (also, there are more thin than thick slabs to the ounce).
Further, many peghead patterns require oversize blanks (e.g. Gibson Flying
Eagle and Bella Voce), so if you have such special requirements be sure to
discuss them with the supplier. Most suppliers do not "grade" mother of
pearl (except to separate the "gold" pieces, which have a specialized
market), because highly figured pieces are scarce enough so that the cost
of sorting by hand would multiply the final cost of the pearl manyfold.
The end-user should pick out the especially attractive slabs from any
given batch and stash them away for the ultimate inlay job. In any case,
use as plain and routine a selection of pearl as possible for your first
cutting efforts.
The inlay design is dictated by the nature of your project, and for this,
you must choose carefully. Please do not commit a fine instrument to your
first inlay project, but don't use a clunker either. I think that the
best instrumental candidates for practice material are instruments you
have built yourself or instrument necks you have built or purchased. You
might consider a medium- priced commercial instrument, one that is
unlikely ever to be collectable, but you will have to strip and refinish
the peghead, de-fret and refret the fingerboard, etc, none of which is
simple and all of which increases the likelihood of failure. I really
can't recommend altering even these instruments. Whatever you decide,
please do not tamper with a collectable instrument--the value of your
1960's D-28 for example, will decline substantially if you alter its
factory appointments, even if you do a first-rate job. Do it to a 1930's
D-28 or a Loar and instrument connoisseurs will report you to the vintage
police. Like many others, I started by inlaying a reproduction Gibson
banjo neck, and this is one of the best ways to learn. Most of the 1920's
and 1930's Mastertone patterns are relatively easily cut (especially the
"Hearts and Flowers" pattern), and there are enough pieces in most of the
patterns to give you lots of practice in layout, cutting, and inlaying.
Banjos are generally very amenable to such decoration--in my opinion too
much pearl on a guitar or mandolin is too much pearl, but banjos rarely
have this problem. The various Gibson, Vega, Paramount, and other inlay
patterns are available from suppliers, and for your first effort you
should probably stick to one of those. Try to select a pattern in keeping
with the instrument--a 1920's Gibson pattern looks pretty outlandish on a
Vega long-neck. Still, the important thing is to get to work, so as long
as you don't irrevocably festoon a venerable collector's piece with new
inlay you should be fine. You could also just do a box, a cribbage board,
or something similar.
If you are more adventurous and want to design your own pattern, by all
means do so. Get ideas from extant patterns, Grecian urns and columns,
$100 bills, TV test patterns, classic museum architecture, kitchen
fixtures, chandelier displays, or deep within yourself, and draw them on a
piece of translucent graph paper (I use Clearprint 100% rag, 10 squares to
the inch, which is available from art suppliers--megabucks but worth it).
I do script patterns (like my brand name) by writing with a medium-wide
calligraphy pen until I have the pattern I like (and that fits within the
space assigned--hence the translucent paper). Then I overlay a second
sheet of translucent paper on the design and trace carefully around the
edge of the script with a size-0 Kohinoor Rapidograph technical pen and
India Ink (I use Pelikan)--any technical pen or even a "crowquill" with a
fairly fine point and the right ink will work. Other patterns can be done
in pencil, and then traced with the technical pen. If you design your
first pattern, you will undoubtedly discover later as you are attempting
to cut the pearl that not all designs can be cut. Try to remember as you
design to keep straight lines straight, and curves as segments of a
circle, rather than as ovals. Remember that you will not appreciate your
design fully until it is embedded in the wood, after it is much too late
to change it, so try to keep it simple and elegant, especially the first
time out.
Lay out the pearl slabs on a table and examine each one to determine the
best side, and remove the figured pieces and put them in the safe deposit
box. Take your purchased or drawn pattern, make sure you have lots of
accurate photocopies, and with scissors cut out the individual designs. I
number each piece of the pattern so that all can be accounted for when the
layout is complete. Glue (with Titebond or white glue) each paper pattern
piece to a piece of pearl, and let the glue dry completely. Be sure to
glue edges and corners adequately, because these are likely to lift during
the subsequent cutting if not glued well. I have tried rubber cement and
contact glue and both have failed to hold the design in place along thin
areas and at corners. At least one of my correspondents designs patterns
on the computer and prints them on laser printer adhesive labels, an
approach definitely worth trying. Otherwise, use a very thin coat of
Titebond or white glue (thin to avoid gumming up the saw blade), and after
the glue has dried, it is time to cut the inlays (the use of Titebond or
white glue is still optional--if you like some other glue, try it). Clamp
your cutting jig to a table and set up the worklight. Install a blade in
the jeweler's saw, and make certain that the teeth will cut on the
downward stroke--the teeth should point toward the saw handle. Use the
tensioning screw to tighten the blade so that it yields very little when
plucked like a string. When you install the blade, be especially careful
to avoid bending or twisting the ends, and make certain that the blade is
as straight as possible. Put on your dust mask and goggles and fire up
the CD player or the radio. There are peaceful but meticulous times
ahead.
To cut inlay well requires only that you be able to follow a line with the
jeweler's saw. This was easy to write, but if you are like most it will
take many inlay-feet of cutting before you achieve the consistently
smooth, graceful line that characterizes expert work. Patience is not a
virtue when cutting inlay, patience IS cutting inlay. Many artisans like
to cut along the outside edge of the line, which they endeavor to keep to
the left of the blade as it lays on the jig. The left hand steadies,
moves, advances, indexes, and turns the pearl slab over the hole in the
jig and the right hand holds the saw handle beneath the jig, and saws up
and down (remember, set the teeth so _down_ is the cutting stroke) and
cuts the pattern. The saw should advance, turn or otherwise move very
little (except up and down)--that's why the hole in the jig can be so
small. Examine the pattern thoughtfully before you start to cut. Look
for inherently weak areas, and plan the best route for the initial cut.
Cut into the slab near the end of a point or corner--if you are cutting
out a star, try to intersect the pattern at the apex of a point rather
than somewhere along a side. When you hit a tight corner, back up the
blade, cut a bit into the outside to widen the kerf, repeat if necessary,
and use the widened kerf to turn the blade around the corner. Try to cut
from weaker parts of the pattern into stronger sections, but frequently
this will be impossible. Endeavor to cut long straight lines and curves
without stopping, because a small bump or ridge often results where the
cut is interrupted. Try to use the entire blade for each cutting stroke,
except when you are approaching a stopping point, but even here keep you
sawing movements as smooth as possible. To cut out "blind" interior
sections, drill a hole into the blind pocket with a pointed bit in the
Dremel high-speed drill, and then thread the saw blade through the hole
and install it into the saw--this is tricky and a threaded blade is
difficult to tighten, but you will improve with experience. Cut the blind
sections first, and for that matter, if you have delicate sections that
are not blind, try to cut them first as well. As your skill improves,
your pace will quicken, but be careful not to cut too fast because the
blade will heat up and break. The other principal reason blades break is
that they bind in tight corners or from being forced to turn too tightly
to follow a tight curve. Blades also break when the metal fatigues from
use, or simply because they get dull. Again, be sure you have lots of
blades on hand. Blades usually just break without causing problems, but I
have had partially-cut inlays break when the blade broke. Once in a while
a blade piece will fly when it breaks, hence the recommendation to wear
goggles. Of course, you have been wearing a dust mask on your face (not
on the top of your head) during the entire cutting process. The blade can
also loosen somewhat during the cutting, which actually makes it easier to
cut but it wanders aimlessly. Be alert for this and tighten as necessary.
If this is a chronic problem, clean the blade attachment points or buy a
better jeweler's saw frame. When the inlay is completely cut, carefully
examine it for problems and then put it in the safe deposit box along with
your figured pearl and family heirlooms.
As I said last time, do not rely on a file to smooth rough edges on your
inlays. The pearl is quite hard and it is difficult to hold small,
delicate inlays tightly enough to file without breaking. A small sanding
wheel in a Dremel can be useful for some smoothing, but in general try to
cut smooth lines with the jeweler's saw so that you don't have to try to
improve the inlay after the cutting is finished. Also, do not attempt to
inlay broken pieces, glued or not. Throw them away, save them for
practice, whatever, but don't try to include them in a fine inlay job. If
you proceed slowly and carefully, your skill will improve dramatically
between the time you start and finish your first elaborate pattern, so
much so that you will probably want to recut some pieces that are not on
quality par with others. Rest assured that this skill will always
improve, no matter how much experience you have, and you will become more
critical of your own work as experience accumulates.
When you have cut all of the inlays, scrutinize them carefully-- compare
and match paired patterns (such as opposite petals in the hearts and
flowers pattern) so that the final product reflects care and attention to
detail. Reject any inlays that are really clunky, but for a first attempt
don't be too hard on yourself. However, the really meticulous (and
irreversible) work is soon to begin. Don't commit substandard inlays to
it, for once your patterns are inscribed in wood, it is difficult to
change your plans.
Afterword: The above applies as well to other materials commonly used for
inlay. These differ physically from pearl quite substantially, but none
is especially difficult to cut. Wood veneer should preglued to a paper
backing before it is cut. Bone for inlay should be at least .06" thick,
which is somewhat thicker than most pearl slabs, because thinner bone is
generally too translucent to make good, contrasting inlays. Sheet brass
is fairly easy to cut, although somewhat harder on jeweler's blades than
is pearl. The use of ivory is rightly controversial (although I'm not
convinced that the lives of the oyster or the ebony tree are any less
valuable than that of the elephant), but should you wish to inlay some old
ivory, it cuts quite similarly to bone but is slightly less translucent.
Old piano key tops are a common source of inlay ivory, but these tend to
be quite fragile and are very translucent. Best to avoid ivory, but it is
a lovely material.
Part III--Routing and inlaying
By now you should be finished cutting your chosen pearl pattern, and you
are probably tired of repeated trips to the safe deposit box. Undoubtedly
you have been staring at the Dremel Moto-Tool and the router base that you
purchased after you read Part I and wondering what they do. Now you shall
find out.
Go to your safe deposit box and retrieve your entire inlay set, and
arrange it on the table in the proper orientation. With a pencil, label
each inlay, and draw a small arrow that points toward the end of the
peghead. The arrow is only necessary for those pieces that are part of a
radially or bilaterally symmetrical arrangement with several identical
pieces, such as petals of a flower. Once you have scribed and begun to
cut the mortises, you must avoid confusion as to the precise location of
each piece. From this point forward, you must not change your assigned
positions--to do so will result in confusion, broken inlays, and problems
during the final inlaying process. This is your last opportunity to recut
any inlays that are not on quality par with the others, and to rearrange
and rematch pieces to best advantage.
The next two steps are really the most critical in the entire inlay
process. Up to now, if you broke an inlay or your pattern was uneven in
quality, the problems were fixed easily by cutting new pieces. After you
(temporarily) glue your inlays in place and scribe the patterns into wood,
it will be tricky at best to replace any, so take special care not to
break any or to change your mind about placement or replacement. Glue
your inlays in place on the surface to be inlaid. In my experience, this
is best done with DUCO cement, because this material can be dissolved away
with acetone (Fire and toxic hazard! Use only in well-ventilated areas
away from sparks and flames! Store safely!). "Spot" the glue lightly in
several places on the bottom of the inlay, and press the pearl firmly in
place on the surface. Script inlays (written text) are especially tricky
and obviously fragile, and should be glued thoroughly on the bottom.
Endeavor to clean up as much of the glue squeeze-out as possible while it
is still soft. Double-check that all inlays are properly positioned
(remember: guitars are inlaid on the 9th fret, banjos and mandolins on the
10th), and set the object aside for at least 24 hours. I used to use
white glue instead of DUCO, but had problems removing the inlays--the only
options are to pry up the inlays or soften the glue with water. The
former can result too easily in broken inlays, and the latter tends to
obscure the scribe lines, so I went to DUCO. Again, once your patterns
are inscribed, it is highly desirable to use the same inlay that was
inscribed, because it is impossible to cut another piece exactly like the
original.
The next step, the most critically important in the entire process, is to
inscribe the inlay outline into the wood. Use the scribe that we
discussed in Part I, and trace around the pattern as close to the edge of
the pearl as possible (which should be flush with the edge), but avoid
undercutting the pearl, and most of all avoid pushing on the inlay itself
with the side of the scribe. At best you could dislodge the pearl (this
only happens, according to Mr. Murphy, to complex inlays and then only
after the outline is about 50% but less than 75% inscribed), and at worst
you could break the inlay--again, this is a calamity if you have already
inscribed much of the outline. If your scribe encounters a mound of glue,
scribe carefully over it several times until it separates from the inlay,
then scribe the wood. The wood grain will tend to divert the scribe
point, so be aware of grain direction changes (relative to the inlay).
Ebony is so hard that it is best inscribed by making repeated passes. Be
slow, be cautious, be meticulous, be a perfectionist. This is your only
chance to do this step correctly, and the quality of your final product
depends on the scribed line (and your ability to follow it with the
Dremel). I have tried to deepen the scribed lines later, after the inlay
is removed, but with very limited success. Even though the pearl is not
supposed to be a "fence," its presence offers a much better visual limit
than does the scribed line alone. Inspect each scribed line carefully and
make certain that all are complete and deeply inscribed. With a glass
eyedropper, dribble some acetone carefully around each inlay, but just do
one or two at a time.
*BE EXTREMELY CAREFUL NOT TO ALLOW ACETONE TO CONTACT FINISH OR
PLASTIC BINDINGS, AS IT WILL CORRODE THEM. ALSO, REMEMBER THE FIRE
HAZARD! A NEARLY EMPTY CAN OF ACETONE IS A POTENTIAL BOMB! THE
FUMES ARE TOXIC!*
After the acetone has contacted the inlay for a few minutes, gentle side
pressure will usually dislodge it. Allow very delicate inlays to soak up
the acetone for at least 30 minutes, and then use the gentlest side
pressure distributed over the entire inlay to dislodge it. It will be
almost the ultimate in disheartening feelings to break it now, exceeded
only by breaking it later. After each inlay is dislodged, take a moment
to clean the residual glue from the inlay bottom and crevices, and renew
the label and arrow (the acetone may tend to disperse the pencil marks,
and it will dissolve away virtually any ink). Arrange the pieces
carefully because you don't want to make any fitting mistakes attributable
to picking up the wrong piece during the routing process.
Now comes the three-step routing process, the most difficult part of inlay
technique to do really well. You must wear goggles and a dust mask, you
must keep a steady hand, you must STOP if you can't see clearly where you
are cutting, you must cut very slowly, and you must keep the faith in your
scribed lines, even though many times they don't seem to be correct. The
first step is to cut the inlay outline deeply with the pointed dental bit
(again, the pointed bits offered by Dremel tend to be too large, but they
will work for many larger inlays, as long as there aren't tight corners).
Use the Dremel freehand, not in the router base, and cut downward and
sideways with the point of the bit from the line into the wood. Hold the
drill like a pencil and use the lowest speed, but vary this to suit the
hardness of the wood and the part of the outline you cutting. This is
actually the most difficult of the three steps, and it must be done
slowly. BE SURE TO CUT INSIDE THE LINE!! Only experience will help you
improve, but this step will establish how "close" your inlays are, that
is, how much filler space results. Try to cut 2-3 millimeters down into
the wood. If you can't see your scribed line clearly, stop and rearrange
the workpiece until you can. I use two or three 25-pound bags of #7 lead
shot (available from shotgun reloading suppliers) to pad and support a
typical neck. These give great flexibility on repositioning and do not
dent or nick the wood. Cut completely around the inside of each scribed
line, and examine each very critically to make sure they are of uniform
depth and that the corners and tight curves are cut vertically and
cleanly. When you are satisfied go back over the workpiece visually once
again. I have never failed to find spots that needed work, even after two
or three examinations.
Next, chuck the router bit (not the ball-end bit) into the Dremel, and
mount the Dremel in the router base. Leave enough bit exposed so that it
will cut a mortise to about 95% of the thickness of your inlays. To
check, use scrap wood and adjust the bit depth so that one of your inlays
protrudes just slightly above the mortise. If you are doing large inlays
in a curved surface (D-45 hexagons in a guitar, for example), your
mortises will be curved as well unless you shim the bottom of the router
base with tape so that it rides perpendicular to the peak of the
fingerboard. For these inlays, set the depth to 95-98% of the pearl
thickness. Straight router bits function best at very high speed, so use
the highest speed setting. Use the router bit to remove as much of the
inlay mortise wood as possible, but be careful not to encroach the edge,
because this bit will cut really fast and do terrible, irreparable damage
if it is not controlled very carefully. As before, if you can't see very
clearly, STOP and rearrange the workpiece so that you can. Cut out all of
the mortises and then examine them critically. Do not yet attempt to fit
the inlays, because the mortises are not quite ready, and you may break an
inlay if it binds in a mortise.
Now chuck the tiny ball-end bit into the Dremel (leave it in the router
base) and set the bit depth so that the ball cuts flush with the bottom of
the routed mortise. However, if with this setup the top of the ball is
flush or within 1mm with/of the wood surface, the bit must be set deeper
because otherwise it will greatly enlarge your mortises. You are going to
undercut the edges of the mortises, and if the ball is too close to or at
the surface it will overcut them too. Ideally, the ball diameter should
exceed the shank diameter somewhat, and should never be smaller than the
shank--the shank rubs against the wood "fence" (the edge that you
established with the pointed bit) and thus keeps the ball from
undercutting too deeply, but it must undercut a little or the inlay may
bind when it is inserted. Use a low or medium-low speed and go around the
edges of your mortises very slowly and carefully with the ball. Be very
aware of the mortise limits, and do not exert any pressure against the
wall of the mortise with the bit shank. Otherwise the spinning shank will
tend to erode the wood and enlarge the mortise, and unfortunately you will
be unable to see this because your scribed lines are gone. Tight corners
and narrow curves may not admit the bit shank, and so these will be
unreachable with the ball. Use the pointed bit freehand again to undercut
these. When this job is complete, inspect each mortise carefully and
recut any questionable spots. It is not unusual to spend hours with each
large mortise (and sometimes with small ones as well)--be prepared to
devote lots of time to a large inlay project.
Now remove the Dremel from the router base and chuck the pointed bit, and
begin fitting the pearl inlays in their mortises. Once again examine each
mortise for any rough edges or uneven lines, and smooth them carefully
with the pointed bit. Gently press the inlay into place. If it won't go
in easily, stop and find out why. Some inlays go a short distance and
bind, and then yield to slightly greater pressure and slip in to full
depth. This is undesirable-- remove the inlay, find out where it is
binding, and smooth the edge. If you don't, even slight expansion of the
wood during seasonal changes may crack the inlay. Tight spots are usually
visible after the inlay is removed because the pearl leaves a white mark.
Examine such spots carefully and decide how deeply to cut-- this is the
place where all of your careful early work can be compromised by
impatience, so use good judgement about enlarging the mortise. Remember
that you followed the scribed line accurately (you did, didn't you?), so
any binding has to be the result of little ridges and bumps on the mortise
edge between the top of the ball-cut and the surface of the wood. Look
carefully for these and smooth them a little, then try to fit the inlay
again. I have modified a discarded dental "elevator" into a tiny chisel
for cleaning out areas that will not admit even the tiniest of dental
bits. I don't need it very often, but when I do nothing else seems to
work. It is relatively rare for any inlay to fit perfectly on the first
try, but it will become more common as your skill and experience
accumulates. Now and again a delicate inlay (especially script) will
become wedged in the mortise so that it is very difficult to remove. You
must resist the temptation to 1) pry it out other than extremely gently;
2) leave it in place and attempt to pack filler around it. Work very
carefully with toothpicks around the edges, and lift it out. It will
come, but if you don't work carefully it will break. Then find out where
it is binding and smooth the edge.
Once all of the inlays are fitted they can be glued into place, and any
gaps between the pearl and the mortise edge filled at the same time. The
process is simple: fill the mortise with a glue/filler, press the inlay
into place, level it, allow the filler to set up, and file, scrape, and
sand the inlay flush. The standard glue/filler has been epoxy with dust
from the same type of wood mixed in for color and texture. This works
well with ebony, but less so with rosewood--finely-divided rosewood dust
mixed with epoxy is usually much darker and greener than solid rosewood.
Some artisans use tinting colors, such as are used to tint house paint,
with some success for rosewood, but I have yet to see a perfect match for
rosewood with any coloring system. I just use rosewood dust and try to
keep the mortises as close as possible.
My pearl inlay mentor experimented during the 1960's with various epoxy
brands (five-minute epoxies were unavailable at the time, so he worked
with overnight-cure material) to find those that set up hard (without a
tacky surface) and that crept minimally--epoxies are technically fluids
even when set, and tend to flow just like water, except much slower.
Really creepy epoxies soon leave gaps and pits in the fill space, and a
superior inlay job can end up looking very inferior. My mentor selected
Wilhold epoxy (standard disclaimers, remember?), and I followed his advice
with good results. Unfortunately, lately I have been unable to find the
correct material--a long-setting yellowish two-part adhesive. I know that
many are using five-minute epoxy, and I guess this is all right except
that one must mix several batches in the course of an inlay job, and many
of these preparations never lose a slight tack. I think the best material
is the light-colored long-set material, and recommend that you find and
use it if at all possible. Whatever epoxy you use, be sure to mix
dead-equal quantities of resin and catalyst, as a mixture of unequal
quantities (particularly an excess of resin) tends to creep. I make up
the mixture, stir carefully to ensure uniformity, and mix with just enough
wood dust to yield a fluid mixture of the correct color. In my
experience, the best dust is produced by filing wood with a metal file, as
other dust may be too coarse or may be mixed with "impurities" (sandpaper
abrasives, etc).
If you are using long-set epoxy, you can fill all of the inlay mortises to
about 3/4 depth with the epoxy filler. If you are using five-minute
material, only fill one or two large mortises at a time. I emphasize
this--if your epoxy sets up before you embed the inlay, you will have to
re-rout the mortise. After the requisite number of mortises is filled,
press each inlay into place, and level it by rocking gently with a couple
of toothpicks or thin dowels. Another advantage of long-set epoxy is that
there is time to self-level prior to embedding the inlay. Embed all of
the inlays and double-check each to make certain that they are seated to
full depth and that filler has oozed all around. Be especially careful
that none are tilted. In the past I have applied heat from a
high-intensity reading lamp to each inlay-filler to increase fluidity and
allow bubbles to escape, but this practice is now discouraged because it
has been shown that most epoxies liberate toxic gases such as phosgene
when heated. This practice also accelerates the cure, so that long-set
epoxy when heated may harden in just a few minutes. In any case, allow
the epoxy to harden completely before proceeding.
The final steps are to clean up the excess filler and level the inlays
with the surrounding wood. I use a cabinet scraper (sorry I forgot to
mention this in Part I), a double-cut mill file (ditto), and a hard rubber
sanding block with various grits from 80 (pretty coarse) through 600
(pretty fine). Start with the (dull) scraper and shave away the epoxy
from around and on top of the inlay. Be very careful in this and the
following steps not to gouge or otherwise damage the surrounding wood.
Continue to shave until most of the epoxy is gone. A coarse file can take
the process a step further and begin to level the inlays with the wood,
but again please be careful not to dig into the wood. Finally, use the
sanding block alternately with the scraper on each inlay (avoid the
surrounding wood, because it is much softer than the inlay and will erode
at a much higher rate--this will result in high and low spots). Change to
120 grit after the inlays are completely leveled and flush with the wood,
and sand carefully to remove the 80-grit scratches. I emphasize--use a
sanding block, or at least use cork- backed sandpaper... ...do not use
your fingers as a sanding pad for this or any other operation in lutherie.
If large bubble holes show up in the filler, take an extra day to fill
them and to cure the new epoxy, then level with the sanding block and
scraper. After the 80-grit scratches are gone, move on in turn through
220, 320, 400, and 600 grits (all used dry). Sand the entire fingerboard
with all of the grits from 220 and finer. By the time you get to 600, the
inlays should be free of visible scratches and they should look pretty
good against the dark wood. You should be beaming with pride....
Carefully clean out the fret slots with an X-Acto knife and #11 blades,
and with a vacuum cleaner hose before you attempt to install frets.
I don't oil fingerboards, other than to allow skin oils to put the
characteristic patina in the board with time and playing. I have found
that a final vigorous polish with a cloth diaper or dish towel does at
least as nice a job as oil on the board and inlays, and doesn't add any
chemicals to the wood, so I recommend that over any oil, plant-derived or
not. If your pattern involves engraving, now is the time--this is beyond
the scope of this discussion, as it is one of those processes that is
technically easy but takes vast experience to even begin to master. Buy
some gravers, draw some lines on the inlays, follow the lines with the
graver(s), use jeweler's wax or the epoxy-ebony dust mixture to darken the
lines. Just keep doing that until you're good at it.
Dot inlays: Purchase the correct dots, purchase a matching (preferably
brad-point) drill bit, purchase a drill press. Do not attempt this with a
hand drill. Drill the holes to nearly full depth, press each dot into
place, put a drop of cyanoacrylate glue (Crazy-Glue or similar) around the
edge of the inlay, let it set up, sand off the glue and polish as above.
And while on the subject, some of the old Gibson Mastertone patterns use
small dots in floral array--buy these, don't try to cut them with the
jeweler's saw.
I'd be interested in hearing what others are using for inlay filler these
days, as the good epoxies are ever scarcer. Your input on or off the
newsgroup is most welcome. Again, my thanks for the positive feedback
from earlier parts, and I hope you have found this segment worthwhile as
well. If interest abounds, I'll write about other lutherie operations as
the time and my experience allows.
Sean Barry (sjbarry@ucdavis.edu)
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