Mother of Pearl Inlay Technique, Part I


Epiphone Sheraton II with Mother of Pearl Custom Guitar InlaysThis 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:

Triangular Cutout Jig for Cutting Custom Guitar Inlays

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…


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