I recently learned a new thing (to me) in low-temperature casting: hollow forms cast in tin. It’s a medieval practice, easily documented, and used for an exciting variety of forms, including ampullae, whistles, bells, wearable vases, and even tiny reliquaries, as ten minutes of happy searching through the Kunera database showed me. (Go look for yourself! It’s awesome!)
The pewter I ordinarily cast with is 98% tin, but that 2% makes a difference. Pure tin stays liquid longer than pewter, not going through a ‘slush’ stage as it cools. This means that it can be poured into a mold, then dumped out, leaving a thin layer of hollow metal in the mold.Tin tends to be a bit softer than the pewter I use, but not prohibitively so.
Why would you want a hollow form instead of a solid one? With some things (bells and whistles), it makes them work as instruments. Ampullae and reliquaries are intended to hold material from a sacred site or person, so a hollow is essential. Of course, a hollow item is also cheaper to produce, as it uses less material.
A mold for a hollow form isn’t much different from one for a solid piece. If it will be two-sided (having carving on both faces) or even more complex, the mold will need to be fitted with registry pins so that the pieces
always fit precisely. These are simple enough: drill through one side and into the other a bit with the pieces fitted exactly as you intend them to be. Widen the openings at each end of the drilled holes. Heat the mold, fit it together, and pour molten tin into the holes. Wipe off excess with a gloved hand and allow to cool. Why use tin? Well, although in period, pure lead was used, if there’s a problem with your mold, you may need to put the whole thing in the pot to melt out a locked casting. The pins will melt out, too, so unless you want another metal in your tin pot, you may as well use the same thing for every part.
Because the tin needs to be poured back out, the opening for the pour must be wider than usual, and the body of the hollow also is wider than a flat form would be, to ensure some liquid tin will be able to pour out. You’ll need to watch the temperature of your mold carefully: a hot
mold won’t cool the tin quickly enough, and if you don’t wait, it may pour out half of your design with it. Of course, if you have really thin parts (like filigree, pin backs, etc), you’ll want your mold to be warmed up, or they won’t cast. It will take practice, but as with pewter, if it doesn’t come out, put it back in the pot and recycle it right away.
The open edge will vary depending on the type of item you are making. No matter where it is, you will want to clip off the excess once it cools. You can finish by filing or tumbling if desired. You don’t have tremendous control over thickness with this method; if you want the interior to be very smooth, you may need to do finishing work on it. If you want an exact thickness, you may as well use a wooden plug or other means to ensure that and cast with pewter. However, for odd-shaped pieces where a plug will not work, and for pieces that don’t need to be precise on the inside, this is an easy, medieval period method that works well. Happy casting!
In the SCA, the Kingdom I live in is The Kingdom of Caid. In modern terms, I live in inland southern California. My home is on land zoned rural-residential, overlooking a major freeway. This means, among other things, that we can keep chickens and other animals that not everyone is allowed to keep. Since we were going to get chickens, I figured it would be fun to specifically get some breeds that were known in period. I wrote a brief introduction to them for display at our recent Festival of the Rose, and have expanded it somewhat for this post.
Warning: I have not delved into the archaeology of chicken breeds in anything like the depth that I have for intaglio carving. I’ve been keeping chickens since early 2014, and what I’ve learned, I’m happy to share. I am a member of Backyard Chickens, which I recommend as a good starting point for information on chicken-keeping and connecting to your chicken-keeping neighbors. Please remember that chickens are a ridiculously over-regulated animal, and many areas will not permit you to keep even one hen, let alone a flock. Check your local and county ordinances regarding livestock before getting chickens. A chicken is a real commitment: they can live thirty years or more, regardless of the average production chicken’s lifespan.
Period chicken breeds are all what are now called ‘heritage breeds’, which are different from modern ‘production breeds’ in several ways. Heritage breed chickens produce fewer eggs and less meat than production breeds in their first year or two, but where a production hen rapidly produces fewer eggs after her second year, a heritage breed hen will continue to produce at peak volume for five to seven years, and then still produce some eggs for many years after that. Heritage breed chickens tend to be better parents and are generally healthier and more able to fend for themselves than production breeds. They forage well, and watch out for predators (with a notable exception below). Heritage breeds have been less favored in the interest of making massive profits in the food industry; however, for the small farmer or backyard chicken keeper, there are many reasons why a flock of heritage breed chickens would be better to keep than production birds. Personally, I like the personalities and beauty of the heritage breeds, and wouldn’t trade them for any number of optimized producers.
Meet Our Chickens
Sitting on my shoulder is Nova. He is a black rose-comb bantam rooster, a breed that was established in England in the fourteenth century. Intelligent, handsome, and tiny, he is a fierce protector of the youngest of our flock. In the photo, he is perhaps two years old.
I got Nova for free from a Craigslist post advertising him as a White-Faced Black Spanish bantam – another period breed. However, as you can see, his face is not white. Also, the rose comb is a dead giveaway. The previous owner said he was flighty and not particularly friendly, but I had driven a long way to get him, so I gave him a chance. When I got him home to the coop, I sat down and opened the cat carrier he and another rooster had ridden home in. He came out of the carrier, hopped onto my knee, hopped onto my shoulder, and started talking to me and grooming my hair. He’s been my little friend from that day on, and I have never regretted the long drive to go get him.
Dots is an Old English Game Bantam rooster. Beautiful, but aggressive, we gave him to a family that had far fewer roosters, as he can’t resist arguing with them. This breed was developed in medieval England specifically for fighting. They can have different types of combs, but this little guy has a rose comb like Nova’s. Even though he is a bantam, he weighs about twice what Nova does, and every ounce of it is muscle. He is very attentive to his hens, and, like Nova, is an excellent guardian.
Ozzie is a Silkie rooster who I got from the same Craigslist post that gave me Nova. Bred originally in China, Silkies are described in Marco Polo’s journal as chickens with fur. The Mongols traded them to Europe. To this day, their black meat is used in traditional Chinese medicine and cooking, and reputed to treat a number of ailments, including diabetes. Hardy in heat and cold, Silkies are excellent pets and produce medium white eggs. They come in many colors.
Silkies are also some of the best mothers a chicken owner can hope for. They become broody often and will sit, hatch, and raise clutches of babies not their own, and even not their own species. This is Inky, one of our best broody hens, raising yet another baby not her own (a Russian Orloff, as a matter of fact – a critically endangered heritage breed). I often joke that Inky will eat your face if you mess with her chicks… while she is a very cuddly hen when she isn’t broody, it’s only half a joke when she is. She is fiercely protective of her babies.
Docile and friendly, Silkies make an excellent chicken to bring to SCA events and demos. They look very different from most people’s experience of chickens, are a true bantam breed (there are no large Silkies), and are soft to pet. Storm here is actually at a demo in this picture. She sat on the table for several hours, without complaint, and only needed a small bribe of treats to keep her there. Small children and a few adults got to pet her and learn about an unusual kind of chicken, and about trade from China during the Middle Ages. Even their roosters tend to be gentle; we have a black Silkie rooster named Khan who helped the hens incubate their last clutch of eggs. A couple of other things that make them especially unusual: they have ten toes, like we do (most chickens have eight), and, if pure-bred, their earlobes are pale blue.
Thorin is a Polish rooster. Polish chickens, or something much like them, have been kept since Roman times. One of their distinctive skulls was found in the remains of a Roman British settlement. Salt, below, was one of our first Polish hens. Beautiful as she was, her ‘hairdo’ kept her from seeing the hawk that took her, so we no longer let our Polish free range. Instead, they live in a large covered run which the hawks periodically land on, looking frustrated.
Black as coal, this is Yaban, or in English, Midnight. She is a Korean period variety of chicken called the Ogye. Like the fluffy Silkies, she has black bones, skin, and organs, but her feathers are black as well. Ogyes come in no other color, though their eggs are white. Treasured to this day by families who raise them to eat in traditional Korean food, Ogyes are relatively rare in this part of the world, but still common in Korea.
Our chickens are work, I’m not going to lie. Even the most easy-going free-range flock requires care. But we’re reaping benefits we didn’t expect: did you know they cheerfully eat spiders, including black widows? We had a major black widow problem here the summer before we got chickens. They’re a rare sight now. Our larger hens even eat mice. They weed the yard, break down the leaf mulch in the front yard, and absolutely wrecked the pretty color-blocked bark chip beds we had set up on our thrown weapons range. The roosters do wake us up, but they also will defend their hens even at the cost of their own lives, as several did when a bobcat broke into a coop one night. Roosters (good ones, anyway) are actually touchingly chivalrous, calling their whole flock over to eat any special treat they find without a bite for themselves until everyone else has eaten. And the biggest surprise: some chickens really love people. During the day, they have Important Chicken Business to take care of, but in the evening, they’ll cuddle and watch TV with you and try to steal food off your plate if you’ll let them. Nova will fly up to my lap or my shoulder, say hello, and then fly back down to care for his part of the flock (he’s a lieutenant in our bantam and Orloff flock), and it makes my day. Ozzie loves to run away from us, but not too far… he wants us to catch him eventually, and will sit on a towel on the couch politely while I go to the kitchen and get my dinner.
I guess what I mean to say is, I love our little dinosaurs, and I think they don’t get enough credit for being awesome animals in addition to being ‘livestock’. And fresh eggs… they’re a whole other thing.
So, now we know that even during Intaglio Fancytimes ™ the carvings weren’t usually all that fabulous, or easy to see, and that for all that we love the Getty’s amazing collection on display, we also know that they and other museums are hiding hundreds of truly special pieces of the art away so that 5-year-olds everywhere don’t get the idea that they, too, are ready to carve innocent pieces of semiprecious stone.
Now, let’s move past the first Intaglio Fancytimes I ™, aka the ancient Greek/Etruscan/Roman period of At Least Some Mastery, and start looking into the long dark teatime of the art, before Intaglio Fancytimes II ™: The Renaissance Goes Nuts (especially those Medicis) and Intaglio Fancytimes III ™: The Victorians Try To Do One Better. Worth noting: intaglio was already an old art by the time Fancytimes ™ happened at all; intaglio seals were made and used by ancient Egyptians, Harappans, and Mesopotamians, so it’s really no surprise that it was a very fancy art with specialized equipment and trade secrets.
Intaglio carving didn’t die out. It was adopted by various cultural groups, and remained a lively and valuable art throughout the intervening centuries. Remember, this was a means of identity protection during a time when you couldn’t be sure who wrote what, and certainly couldn’t call anyone up to check. In addition, intaglio carvings continued to have sacred significance.
The sixth century seems to me like a good place to start looking for an intaglio tradition beyond the Roman, and I was not disappointed. In Persia, the Sasanian tradition included extremely tiny carvings (on stones less than 1 cm in diameter), generally of animals. The carving is on the left, with an impression from it to the right, blown up. Yep, that’s definitely some sort of bird. The stone is carnelian. Medieval people loved carnelian. This piece, by the way, is one of the gems hidden away on paper in the Getty catalogue, titled Ancient Gems and Finger Rings.
The easiest way for me to figure out what shape bits were used is by trying to duplicate the carving myself, which I did. Simple though the carving is, I used four bit shapes to duplicate it: a medium pellet (ball-ended bit) for the breast and body, a small pellet for the head and some work on the neck, a small barrel (cylindrical bit) for the neck and legs, and a tiny wheel for the feather-lines, feet, and beak. These bits all needed to be used wet to prevent chipping, but that was a given, as diamond-encrusted bits hadn’t yet been created. Instead, the bits were used to push a slurry of sapphire or emery powder in oil against the stone (for more detail, look at my posts on The Machine). The images here are all the originals, by the way.
Recently, a 9th century Viking grave find from Birka was all over the news. While it had been dutifully catalogued and put away, the original analysis left out a few important points and got another one wrong entirely, and this was great news for us, because it meant more attention was being paid to Medieval intaglio. The medieval Islamic tradition of intaglio carving follows the religious injunction against creating likenesses of living things. Typical of this tradition, the Birka intaglio contains only a line of writing with a religious message. To the right is a more intricate design of the same tradition. In my effort to replicate this piece, I used three bits: a tiny pellet (most of the carving), a tiny wheel (outlines), and a point which I had little luck with. What I really needed was an even smaller pellet.
At the same time, a very different intaglio tradition was rising in the Carolingian empire. With a special fondness for rock crystal (clear quartz, to the geology folks), the Carolingian intaglio carvers could bring the stones down onto the rotating bit as they carved while looking through them, seeing immediately the effect of every single tool-mark. They didn’t need to reverse everything they carved, as long as they used clear quartz; they merely had to look at the top face of the quartz and mark it as their vision dictated. They also had a fondness for really big pieces of stone, which makes sense when you realize that these large pieces are not personal seals, but parts of processional crosses and other ritual items. These were meant to impress from a distance.
When I recreated Radpod’s likeness, I used four bits: small and large pellets, a small barrel, and a thin wheel. The wheel was for writing, hair, eyelids, and folds in the cloth. The large pellet made the curves of his head, face, neck, and shoulder; the small, his chin, ear, lips, and eye. The barrel made his brow, moustache, and most of the drapery. The setting is open on both sides, as this is a seal.
Finally, in the Byzantine tradition, figurative seals return to opaque stones, with saints a particular favorite subject. Alongside the image, text names the subject, much as it does on icons. Everything is in reverse again. I used only three bits for this: medium pellet for dragon body, torso, head, and limbs, small wheel for all lines, and small pellet for all small curves and dots.
The next distinct carving tradition is the Renaissance Neo-Classical, or Intaglio Fancytimes II ™, which starts just as the Middle Ages are winding down, back in Italy once again. First as collectors, then as patrons of the art, the Medici family brought intaglio back to the skill level they had come to expect, in the fifteenth century.
Still precious, still rare, intaglio was produced throughout the medieval era in a variety of styles. Even as ancient gems were reused, new ones were carved, and the skill, already thousands of years old, lived on.
Most people who even know what intaglio gems are have a pretty clear mental picture of what they looked like. They were stunning, tiny portraits of Classically draped people, perhaps athletes or deities, executed with skill unmatched by modern machinery by people with microscopic eyesight and, probably, no social lives. The best pieces were signed, in Greek, and were carved in stone that was either plain in color, or had layers which were used to make the tiny carvings easier to see, like cameos.
Everybody knows that’s what intaglios are, except, of course, people who don’t know what intaglios are at all. And they’re right, for certain, specific times and places. But if you’re interested in the period from the fall of Rome to the Renaissance, loosely called ‘the Middle Ages’, this isn’t what they looked like, unless they were pried out of older jewelry (which they frequently were, by the way).
First of all, it’s really easy to find evidence that patterned stones were considered fair game for intaglio carving, even at what art historians might call the ‘height of the art’. The J. Paul Getty Museum, where I love to go and dream of being an Incredible Intaglio Carver ™, is just full of these suckers. Gorgeous stripy stone, completely obscuring the details of the carving from more than a foot away… except, folks, please remember that these carvings weren’t made to be seen from more than a foot away. This lovely Etruscan piece measures less than 1.5 cm tall. It is highly intimate art, to be seen only by people who could actually touch you, and used to seal documents and prove the identity of the sealer without being easy to copy. From further away, the stone was beautiful because stones are beautiful, not because it has a tiny little dude carved in it. Nobody you didn’t allow near you could tell what, if anything, was carved in your ringstone. It simply wasn’t their business. So, don’t let some patterns keep you from carving a beautiful rock.
Second, I’d like to call attention to the carving to my right. Set in gold, this carnelian carving looks like the work of a first-timer in a hurry. However, it is almost certainly not. It is a Roman intaglio twice the size of our stripy friend above, and clearly valued highly (look at the gold!). Not every intaglio carver was Epimenes, or even remotely close. Carved gems were also valuable simply because they were carved. For every one gorgeous microsculpture on display in a museum, there are literally hundreds of stick-figures, once set in gold and lovingly worn in devotion to a deity, a household, or just for the bling factor. Again, unless they’re really close to you, they can’t tell how good it is. It can be harder to find these online, as museums tend to upload images of the ‘best and brightest’ of their collections from an art-historical point of view, but full catalogues, printed on paper (what?!) often have a much more representative sampling.
Next, on to look at some Medieval-period carvings.
I went a bit overboard on my documentation for a pewter piece I made recently, and learned some cool things I didn’t know. I’m sharing them here; it makes for a disjointed post, but hopefully it’ll be worth a read.
Backings: Small pieces of paper or parchment were used to back some badges. These materials degrade rapidly when exposed to moisture and weather, so all that is generally left for us to find today are the empty, folded-over clips, though one badge from Magdeburg retains its paper insert to this day. Other materials (contrasting metal foil, fabric or leather, for example) were used as well (Spencer, 5). Card stock is a perfect weight, and scrapbooking papers can make really pretty backings. I went a bit further, and painted mine with period paints. I got a great disco-inferno effect with thin brass foil repousseed in a simple diapered pattern of crossed lines, pushed in at the middle of each square.
Alloys: Spencer describes several alloys used commonly in the production of badges found in London, where many fine openwork badges have been found. Most were made using a lead-tin alloy. As tin was many times more costly than lead, cheaper pieces had higher lead content; however, if lead content is too high, casting problems result, including air pockets and a frosted, rather than shiny, appearance. The finest pieces were made of pure tin or a very high-tin alloy, as used in the production of Canterbury bells. The bells were cast in an alloy containing approximately 97% tin, 2% copper, and the rest bismuth and sometimes antimony, but no lead at all (Spencer, 11). The pewter I customarily use is fairly close to this alloy: 98% tin, 1.5% bismuth, and .5% copper (Rotometals). Coincidence? 😉
How thick is thick? Like many others, I have heard from various sources in the SCA that period pewter was always cast as thin as possible. This makes sense from an economic standpoint (metal isn’t cheap). However, how thin was ‘as thin as possible’ ? I chose the Portable Antiquities Scheme database in the UK for a brief survey because it routinely includes data on thickness, rare in other sources. I did a broad search for medieval-period badges which had been published (and therefore verified as to authenticity and period) and created a table to get a rough estimate of customary thickness in a fairly random sample. I used only the first dozen pieces with a recorded thickness, not including pin backs, integral rivets, and the like, and skipped any ampullae, whistles, and other hollow forms to avoid confusion. Several of the thinnest finds are fragments, and might have had thicker cross-sections. The average thickness of my sample is 3.8 mm, with exactly 6 pieces below and 6 above this thickness. Finally, my archaeology degree pays off.
Finally, not new to me, but trust me, if you like period pewter, you need to visit the Kunera database.
Sub-subtitle: in which I am so very much not in my element.
Well, now that I knew what it should look like, I had only a couple of problems. I’m not much of a woodworker. I’m also an ornamental metalworker, not a machinist. So basically, I was going to need to either pick up two more skills, or enlist help. I considered the first, but in the end, did the second, in the hope that I might thereby preserve some small amount of my remaining sanity for later use.
The main part of the mechanism should look familiar to many people interested in old ways of doing everyday things. It certainly did to me. It is, essentially, a spinning wheel. As it happens, I bought a spinning wheel at a swap-meet some years ago. Not being a string person, I decided to cannibalize the spinning wheel and mount it to a simple table, so I could bring the machine to SCA events and demonstrate intaglio carving, and possibly even teach it to interested people.
All I needed, really, was a detail the picture did not give me: how the different bits were mounted and changed. I know for certain they used a variety of bits throughout the Middle Ages, using between three and five different shapes for most pieces (details of how I know this will be a subject of another post). You can see a giant rack of them on the workbench in the woodcut, as well. Nowadays, we have a chuck that can be opened and closed around the bases of interchangeable bits, but I couldn’t see what they were using in the woodcut. So, having recently discovered that the bounty of JSTOR was available for me to paw through, I headed there and searched. I found an older article with truly abysmal photographs (one of which was almost entirely black) of a Renaissance lapidary lathe belonging to the Medici family and dating to the very end of SCA period, held apparently by a European museum. The drive wheel was hidden in the back wall of the workbench, but otherwise, it greatly resembled the machine from my new favorite woodcut. It even had a picture showing where the bits were mounted. I was pretty excited.
The picture showed a lovely little statue of Atlas which entirely obscured the means of attaching the bits. There was a second, closer shot, but it wasn’t any better. The entirely black picture might have held a clue, but it was, as I said, entirely black. It might have been of anything.
I won’t lie and say I was undaunted. I was pretty daunted. I was also frustrated and a few other things. However, lacking the certainty I wanted, I went to what pictures I did have. One of them showed a bit that might possibly have been square near the base. That, I thought, might be the trick. If the axle of the smaller wheel had a square hole in it, bits with square bases could be made to fit it. The shape would ensure they turned along with the wheel, and the pressure of carving would keep them from wiggling loose. It could work. Was it the definite way it was done? No. But I was stuck with plausible at this point if I wanted to make something that could work, and my frustration level was significantly elevated.
This is the point at which I felt able to ask for help making the thing. A good family friend, known in the SCA as Roger Wells, has the knowledge and skills I lack. He also has a well-equipped workshop, where he often teaches armoring, leatherwork, and woodworking for the medievalist community. I printed out the photos and the woodcut, loaded up the sacrificial spinning wheel, and headed down to see him. I explained what I wanted to build, and brought out the spinning wheel, explaining that I planned to use it for spare parts.
Roger howled. I’d never heard him howl before. “That is an Ashford spinning wheel! You will not take it apart!”
I explained that it had never been properly introduced to me, but it had sat in the desert for several years and was surely in sacrificial shape. He rejected my plans and told me he could heal the thing, so I left it to him, to repair and share with a string person who won’t speak blasphemy about disassembling it. He also said we could make all the parts we’d need. We drew sketch plans for the machine based entirely on the German woodcut, which was by far the simpler design. Although in period, these tools were not meant to be moved, for SCA purposes, some design differences were necessary. Also, to be perfectly honest, my fiance and I were both unemployed at the time, so cost was a factor.
We headed out to the home improvement store for plywood (so it would be light and easy to carry to events), metal, stain, and sealant (so it could sit all day on wet grass at an event). Using his designs, I drew the cut-outs for the two upright sides to help further lighten the piece. He cut the vast majority of the pieces, though I helped a little and did the sanding and finishing.
A solid center upright and a bar across the back would help support the wheel and the treadle, once attached. We hit two snags along the way. One was that neither of us had the means to heat the steel axle for the great wheel to create the angled S-curve that the treadle would use to drive the wheel’s motion. For that, we took ourselves and our steel to Roger’s friend, known in the SCA as Master Luther Anshelm of Anshelm Arms. A master armorer, Luther made very quick work of the S-bend after giving us a tour of his workshop.
The second problem you might have seen coming. Circular holes are quite easy to make, even in steel, even quite narrow ones. Square holes, however, are tricky, at least in a home workshop. So we didn’t really make one. Roger drilled a circular hole as close as he could get to center. Then, once the entire machine was otherwise assembled, I fitted a piece of square brass tubing into the hole, shimming it until it was centered and well, outright cheating by using epoxy to set it in place.
I know my limitations, you see. By this point, I was so close to having this thing working, and I couldn’t stand to wait much longer. If I were a real tool-making, forge-working metalsmith, I would have done some metalworking magic and either drilled and chiseled an approximate square hole, or I would have used heat and appropriate tools to make it happen. But I carve pictures in rock, backwards, and all I wanted was the tool to do that without electricity, so I approximated on the part I have the least proof of anyway. Someday, I may find more information on interchangeable bits in the Middle Ages, but for now, I have a foot-powered lapidary lathe. Hear it whirr. (Really, it gets going pretty darned fast!)
The bits I made initially were made of brass rod. I beat the ends of the brass bits into squareness cold, on a small anvil, with a small and battered hammer I got for free from another SCA member years ago. What is surprising to me is that, for all the eyeball-measurement and hand-hammering and such, once they’re spinning, the blanks are every bit as consistent and centered as the commercial diamond bits I use with my Foredom.
So, here it is, in all its approximated glory. Coming soon, the making of shaped bits, and the carving of actual intaglios on this lovely beast. Also, on a related topic, intaglios of the Middle Ages: what they were, weren’t, and how to make your own in their styles. Spoiler alert: it’s probably not what you’re picturing.
Sub-subtitle: And Why It’s Probably What They Used All Along
The secret of gem-carving was jealously guarded: when Theophilus sought the secrets of the intaglio carvers’ art, the masters of gem-carving in the early 12th century advised him to soften rock crystal in the warm heart of a newly-killed goat, though the secrets of polishing and drilling the stone were accurately recounted to him for his book On Divers Arts.
Period tools for doing this kind of work actually used abrasive powders such as emery, corundum, or even diamond powder, in an olive-oil slurry, on metal bits. For a beautiful video of this method being practiced almost the way it was in ancient Greece, visit the J. Paul Getty’s online exhibit Carvers and Collectors and watch the video in the upper right-hand corner. You’ll notice the carver is using a handpiece on a flexible shaft, attached to a jeweler’s motor like the Foredom I use. It’s convenient, and it’s almost the way they did it. Almost.
The carving would have been done historically using a lathe-mounted drill, powered by a treadle. Bow-drills are popularly cited as the tools used for this work, and are depicted in various places in ancient art including Egyptian tomb walls, sometimes being powered by the artist, sometimes by a second person. Bow-drills were certainly used for making holes in beads and other similar work. However, the use of single-directional rotary tools for intaglio carving has been dated to about 1750 BCE in Mesopotamia by Margaret Sax and her fellow researchers a decade and a half ago. Simply put, they microscopically examined the carvings of seal-stones and found that the carving marks were made from a tool which consistently rotated in a single direction, rather than going back and forth.
It is possible that this technology was rediscovered repeatedly; when it was unavailable, a bow-drill mechanism could have been used instead. The initial scratch-sketch was done using a fragment of diamond or other very hard stone set in a metal tool, but gemstones were not carved using hand-held tools the way soapstone, alabaster, or marble can be. Many gems are harder than steel tools, which is precisely why they are valued for jewelry. In various places and times through period, differing techniques and tools were used. Byzantine and Carolingian carvers used differently shaped bits, and got different results from each other, and from the earlier masters of the art in ancient Greece and Rome. For an excellent source on the Carolingian carving tradition, I recommend Genevra Kornbluth’s beautifully illustrated book cited below. However, looking at her gorgeous macrophotos, I can’t agree with her claim that bow-drills were used at the time; the grooves I see from the carving tools suggest they, like the Mesopotamian seal-stones, were carved by a single-direction rotary tool.
Infuriatingly enough, despite searching almost desperately for four years for anything that would show me what was used, I found nothing useful. Then, two things happened in rapid succession. First, a friend and arts enabler I know in the SCA as Cynthia de Wickersham invited me to the opening of the Gems of the Medici exhibit at the Bowers Museum. Second, I learned that JSTOR had started providing limited free access to their archives to the general public. At the museum bookstore, I purchased the exhibition catalogue. On the second-to-last page, about two inches high, I finally saw the picture that gave me what I needed.