This article is a 3‑part monster from my friend Sean Barry down in Davis, CA. It is bar-none the best article on pearl inlay on the Internet, in my humble opinion. When I was writing my own MOP article for Guitar Inlays Headquarters and researching the subject, I found Sean’s old article and asked him if I could reprint it here. Being the nice guy he is, he not only said we could print it here, but he also revised it with updated information for 2011. I bring you Mother of Pearl Inlay Technique, part I, part II, and part III.
Take it away, Sean…
Mother of Pearl Inlay Technique, Part I
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.
2011 revision:
I wrote “Pearl Inlay Technique” in three parts over about two months in late 1995. I posted the parts one by one in plain text and ASCII art in the old USENET newsgroup system (rec.music.makers.builders and alt.banjo), and the series made its way all around the then fledgling “World Wide Web.” The response from established and aspiring luthiers and inlay artisans was unexpected, gratifying, and to my amazement pretty constant over these 16 years—folks still find the series through some dusty link or another and apparently the articles still resonate with those who want to learn how to inlay mother of pearl. But much has changed since 1995 in the world of inlay and in my world too, not to mention in the way we disseminate information online. Particularly because of the latter I’m somewhat reticent to revise and redistribute the articles, and yet some of the information is sufficiently dated to make me think I should either revise the treatise or search it out and pull it down wherever I find it. Since the latter is impossible and since I still have some creative streaks remaining in my aging frame, I decided to revise the text and float it out there once again.
Acknowledgements:
I want to thank all who took the time to write to me about the first edition of “Pearl Inlay Technique,” and I also want to thank several individuals who started me down this path so many years ago, either through direct instruction and conversation, or through their first-rate writing. Thanks to Donald Zepp, Roger Siminoff, Frank Ford, Richard Johnson, Hideo Kamimoto, Ervin Somogyi, Don Musser, Mike Longworth, and most of all to my good friend Chuck Erikson, the incomparable Duke of Pearl.
The text that follows describes one person’s method for inlaying mother of pearl and similar materials into wood. There are as many variations on each step and indeed on the entire process as there are people who inlay pearl, so if you run across instructions that deviate from the paragraphs below (or vice versa), please adopt or stay with what works best for you. Practice first, so you know which way that is.
I. Materials and tools
Any number of flat or flattenable materials can be inlaid into the surfaces of instruments, furniture, jewelry boxes, 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 interior lining of the pearl oyster (Pinctada species) shell, and although all shelled mollusks possess a shell lining that resembles mother of pearl, the pearl oyster and abalone shell linings are particularly appealing and the shells are large enough to yield reasonably large flat pearl blanks. Oyster mother of pearl is usually white, gold, or grayish purple (“black”) with red, blue, and green iridescence and often with swirl, “eyes,” a curly pattern like “fiddleback” maple, or other figure that results from proximity to the shell 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 they 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 California red and green abalone are the most popular for inlay) occurs primarily in moderately cold water parts of the Pacific Ocean. California abalone for inlay originates entirely from “wild” specimens harvested for their meat, which is considered an ultimate seafood delicacy. Some abalone is now farmed, and perhaps in the future most of the commercial material for food and shell can originate from such sources. Abalone laminates (“Abalam”) are now widely available and are particularly useful for purfling applications and for large inlays in flat surfaces. (2011 note: West coast and Mexican red abalone, formerly the inlay market staple, is now scarce and expensive and it has been largely replaced by western Pacific “paua” abalone and to a lesser extent by green abalone, both of which are also expensive).
Other materials occasionally or commonly used for instrument inlay, at least historically, include bone, ivory, tortoise shell, silver, gold and its imitators, brass, nickel silver, stone and stone composites, 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.
To convert an arched shell to flat inlay blanks requires several steps. 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 in the shell 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 away to reveal the underlying mother of pearl. The resulting piece is anywhere from <1mm to 25mm thick (up to 1″ (25.4 mm) for really thick shells at the lip), and it is still arched. Next the arched blank is fed into a special grinder that flattens and finishes each face of the blank, accompanied by production of much dust. The finished blanks are characteristically no more than 0.06” thick. Many suppliers furnish two thicknesses—thin (about 0.04”) for inlaying flat surfaces, and thick (about 0.05–0.06”) for arched fingerboards. The amount of handwork that goes into planning, marking, bandsawing, and preliminary grinding renders the blanks rather expensive. Blanks may be sold by the piece or by weight–thin blanks when sold by weight are usually more expensive because there are more blanks per unit weight and therefore more labor is involved in producing that unit weight.
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 hand held high speed drill (aka high speed rotary tool) with a router attachment, various bits and appropriate collets for the drill, 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 swing-arm lamp to give best control of angle and intensity. The jeweler’s saw resembles a coping saw with a very slender blade, and the saw and the blades are available from luthier, jewelers, and lapidary suppliers. Blades are typically retailed as “fine,” “medium,” and “coarse,” but the actual thicknesses vary among retailers 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 need for them. Beginners should purchase at least 2–3 dozen blades. Many inlay artisans use a jeweler’s saw with an adjustable throat to accommodate 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 is a piece of hardwood such as maple, birch, or oak about 12″ long x 2–3″ wide x 3/4″ thick. Two common shapes of the business end of the jig include a slot with a small hole a few inches from the end of the jig, or a triangular cutout:
The jig is clamped flat to a table so that the slot and hole or V‑notch extends beyond the edge, the pearl sheet is positioned over the opening, 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 is a 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 and for fitting individual inlays together in larger motifs such as the “vine of life.”
The high speed drill is used to delineate and rout the inlay mortises in the wood. The most commonly used drill for inlay work is probably the Dremel Moto-Tool, which has been in production in one version or another since the 1930s and has a well-deserved reputation as one of the most useful of luthier’s tools. Be sure to check out other high speed drill options such as the Proxxon or the Black and Decker, but do not economize on the high speed drill: purchase a variable speed, ball-bearing model, and if you can afford it, purchase two. Three is not too many. You’ll also need a router attachment for the high speed drill. The choices for this important attachment have changed quite a bit in the past 16 years. I believe that most current Dremels work with the current Dremel “plunge router attachment,” but the base on that device is huge, much too large for inlay work in tight corners. Another option is the Stewart Macdonald “precision router base” (standard disclaimers), which is threaded to fit many post-1995 Dremels. It is a compact well-designed, reasonably precision accessory that is also a bit tricky to learn to adjust and use effectively. Research the alternatives, decide which you like better, and make sure that your chosen drill is compatible with your chosen base before you purchase. I have a couple of old-style Dremel router bases that fit the classic, discontinued Dremel 380, and I confess that I use that old but useful combination for the stages of my inlay work that require the router base. Ebay, as though you were wondering. I modified the router base by replacing the bottom plate with piece of 1/8”plastic 17/8” front to back and the same width as the original base so that the bit is not surrounded by plastic and I can see the operation clearly. With this modified router base I can also access just about any tight corner with the bit. The narrow base setup is prone to tipping but the tradeoff in access and visibility is worth that minor inconvenience.
Numerous bits, sanders, cutting wheels, buffers, etc. are available for high speed drills, but I have found that just three 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 couple of fairly large (1/16″ and 1/8” are good sizes) router or downcut bits. The pointed bit is used in the tool freehand to delineate and cut down the edge of the inlay mortise, the router bit is used in the router base to hog out waste wood in the middle of the mortise and to even up the mortise depth, and the ball-end bit is used on the tool also in a router base to undercut the edge after the mortise is mostly completed. Because most “hobbyist” pointed and ball-end bits are generally too large for small 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. Since the bits were at one time exposed to human cells and tissues ask your dentist to steam-sterilize the bits in an autoclave. If for some reason this is not possible, you could sterilize them yourself in a pressure cooker. Don’t immerse the bits in water in the cooker–sterilization comes from prolonged contact with pressurized steam, which can’t happen if the bits are immersed in water. Instead, place them in a clean tuna can with some marbles for ballast, and place the can in about one inch of water in the cooker. Process for at least 30 minutes on high heat after the cooker seals (the autoclave standard for sterilization is 30 minutes at 250ºF (121ºC) and 15 psi).
You will still need the router bits, and you will need one or more collets for your drill system to match the dental bit shanks which are smaller than most standard Dremel bit shanks (1/8”). Very hard (ebony) or very hard and resinous (rosewood) woods are notoriously hard on router bits unless the bits are made of durable materials like tungsten carbide. Most hobbyist 1/8” shank router bits are not carbide, and the carbide coated general cutting bits that Dremel offers are too large for small inlay routing and they do not cut hard woods very well. For routing work I use carbide spiral downcut bits (aka miniature end mills) with 1/8″ shanks that fit the standard 1/8” collet, available from various lutherie and machine tool suppliers such as MSC. These cut ebony reasonably well, are available in sizes that range from tiny (1/64”) to substantial (1/8”) and except in the smallest sizes they are not expensive which is good because they will probably burn after a couple of hours of use on ebony and probably sooner on rosewood. If you find miniature straight router bits with carbide inserts like their larger siblings have, by all means try them out and also let me know where you found them.
Foredom and similar flex-shaft tools are an alternative to hand-held high speed drills. I am now using a Foredom motor with a Foredom H8 handpiece for the freehand work (see Part III) because the Foredom seems easier to control than Dremels. If you want to use a Foredom for all steps of your inlay work you’ll need to fashion your own complete router attachment to hold a Foredom handpiece (not easy) or to purchase the “precision router base” and corresponding specially threaded Foredom handpiece from Stewart Macdonald.
You can use a padded bench vise or even sandbags 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. 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 and a flat cabinet scraper are useful for leveling the inlays and filler with the wood in the final stages of an inlay project. Other tools you might need include a very small chisel for cleaning inlay pocket corners, gravers and Laskin’s filler if you intend to engrave the inlay, and other bits for the high speed drill as the need arises.
Staying healthy:
Contrary to frequent assertion, neither mother of pearl nor abalone dust is toxic. However, the ultrafine but sharp-edged particles that result from grinding or sawing shell can enter the operator’s lungs and do all sorts of mischief at the cellular level, never ever to be expelled no matter how hard you cough. If you grind shell or saw lots of inlay and thus generate lots of these particles, lots of them can lodge deep in your lungs and could eventually cause serious, even fatal, respiratory disease. The trouble is that the threshold between minor and significant exposures undoubtedly varies with the individual, and no one knows where that threshold may lie for anyone. To avoid inhaling pearl dust you can use a NIOSH-approved respirator, but first consult an occupational health physician for information on medical clearance for respirator use, and ask an industrial hygienist for advice on respirator selection and fit-testing to ensure that the respirator actually protects you.
Hardware store respirators may or may not work, depending on the type of protection the specific respirator offers and on the seal the respirator makes with the operator’s face under a variety of conditions. Only an expert at fit-testing can verify correct respirator fit, but I recognize that many will still opt for the hardware store approach. Half-face hardware store elastomeric respirators should indicate HEPA (high efficiency particulate air) or P‑100 filtration and they should also indicate NIOSH approval. If possible try the fit first by donning the mask with filters in place, breathing normally for a few seconds, then placing your palms tightly over the filter cartridges to block inflowing air. If you can still breathe the respirator is not making a good seal. Try adjusting the straps before rejecting the unit and also try a different size of the same model if available, but if you don’t obtain a good seal the respirator won’t protect you. Also try each unit while looking in various directions, talking, bending over, and changing to other body positions like you would realistically expect to do when working with inlay. If you opt for the lesser “mask” instead of a respirator, purchase (usually disposable) N95 masks that bear the NIOSH stamp. Do not use “dust masks” which offer no protection at all from the ultrafine particles. When you don the mask be sure to squeeze the metal band around the bridge of your nose so that it makes a snug fit. Use the mask even if you cut only a little inlay. If you have facial hair beyond a moustache and no desire to shave you really should consult an industrial hygienist because it can be difficult to achieve a good respirator fit for the hirsute among us and an industrial hygienist can offer the best counsel on this problem.
Using compressed air to blow the pearl dust away from the inlay during the cutting is potentially a bad idea because even a slow and gentle air stream can aerosolize the dust right under your nose, and could transform a minor dust exposure (dust particles released by the sawing) to a significant exposure (invisible clouds of dust). I have the same concerns about vacuum systems, unless they are HEPA filtered at the exhaust (with an efficient prefilter to avoid clogging the HEPA filter). If the pearl dust from sawing actually does obscure the work (it rarely has for me) I recommend that you use a small artist’s paintbrush to sweep away (gently) the accumulating dust.
Getting older:
Sixteen years ago I wouldn’t have dreamed of using an optical magnifier to help me see the pearl I was cutting—magnifiers typically have critical focus that means that being just a bit too near or far from the work results in a blurry picture. Nowadays at my slightly advanced age the choice seems to be between doing sloppy work or using a magnifier so I now use a standard binocular magnifier and have adapted to the critical focus without too much difficulty. These devices range a bit in quality and price—try reading fine print with several different units at various distances and see which gives you the least critical focus combined with the sharpest image.
Continue to Part II, Cutting Pearl…