DIAMONDS ARE A DRILL'S BEST FRIEND
or, THE SECRET LIFE OF BORT
an essay by Meg Berry
The history of diamonds begins with tools. Let us look at the known history of man’s interaction with diamonds.
We find indications of their use as early as 400 BCE in India, and references from then up through history, speaking of this mineral’s brilliance and unapproachable hardness. Pliny discusses diamonds’ hardness, the Chinese refer to it coming from Rome “in iron scribes”. Obviously, the buzz was all about what this stone could do, not how pretty it was. Apparently diamond was valued, traded, and hoarded as a tool for centuries before it was ever considered as decoration.
Imagine a caveman. He picks up a shiny rock, and soon finds that it scratches and chips every other rock he needs to work on. It is a way to make better tools and weapons faster, he has found a treasure that will contribute to his extended longevity, improve his hunting, make him more desirable to a mate, hence assuring the transmission of his genes. So owning this diamond really is forever, and he never even put it in a ring for his fiancée. But maybe she borrowed it to make better needles for sewing furs and tools for cooking, and it made them the warmest, best fed family in the tribe. Not unimaginable that a diamond could be handed down for generations, along with a certain quality of life to which it contributed. This lucky caveman’s descendant could ultimately, coming from a long line of chiefs and leaders, be the mogul who put the family diamond in the first crown.
The first assumed use of diamond in a propelled arbor is from Arikamedu, in southeast India. Examination by Gorelick and Winnett of 9 intact rock crystal beads and 7 incomplete ones found there indicates that propelled diamond drills were probably in use at least as early as 300 BCE. In an Indian text, the Arthra-Sastra, dated 325-296 BCE, a scribe, Kautiliya, describes precious articles being received into the Royal Treasury as “tool-grade diamonds”.
In Arikamedu, there was also found evidence of trade with Rome. It can be assumed that this trade included diamond technology. At the height of the Roman Empire, sapphires begin to appear that had been tooled or inscribed. This is the first evidence of use of diamond tools in the Western world.
Pliny the Elder waxes on about diamonds in Solin-Collecteana Rerum Memorabilia, how their hardness “can be used for marking gems of any kind.”
He also describes the making of a diamond drill so clearly that one could follow his notes today and create a workable drill. “When adamas is successfully broken it disintegrates into splinters…these are much sought after by engravers of gems and are inserted by themselves into an iron tool because they make hollows in the hardest materials without difficulty.” (HN 37.15.61)
The earliest indications of diamond tools in China, which would have brought about a major shift in jade cutting techniques, was concurrent with the commencement of trade with Rome, around 100 BCE. “Kun wu and kin kang were terms used to refer to diamond bladed jade carving knives. The next time we see “adamas” it is being traded between India and the Aegean region around 500 CE so we can be sure that it was present in Europe in some small quantity by the 6th century. More evidence on the historical use of diamond tools is very sparse until the Middle Ages in Europe. By then it is also in use as jewelry, so diamonds as tools lose much of their charm, and their history becomes one with the progress of tools and the Industrial Revolution.
When Leonard Gorelick and A. John G. Winnett were researching ancient diamond drilling techniques for their article in Archaeology Today (Oct 1988, p. 547-552), “Diamonds From India to Rome and Beyond”, they developed a unique method for examining drill holes without destroying the beads.
Silicon impressions were made of the holes, and essentially turned inside out to examine in a scanning electron microscope (SEM). Gorelick and Winnett were able to identify a distinct drilling “fingerprint” that was consistent in each bead or broken piece they examined. It consisted of a perfect cylinder shape on each hole, not the biconical pattern expected from most primitive drills, and a very regular, almost machine-like regularity in the broad, concentric grooves lining the holes .Iron or softer stone drills, even using an abrasive powder, produce a completely different groove pattern.
These unique drilling patterns were shown to be consistent with beads from Ban Don Ta Phet dated to 1-2nd century CE; 56 quartz beads and pieces excavated in the 1980’s in Mantai, Sri Lanka, dated stratigraphically to 700-1000 CE; as well as a modern bead factory in Cambay, India They were able to reproduce the effect with a narrow iron rod, embedded with two diamond crystals about the size of a cucumber seed, hafted into a wooden spindle, powered with a bow, almost the same tool currently being used in Cambay. The beads drilled with the modern reproduction help substantiate their hypothesis of double diamond drills being in use from at least 100 CE. They were unable to reproduce the hole patterns with single diamond drills.
The researchers questioned why in Cambay the stones were still being drilled the old way with bows turning the spindles, when there were electricity and power tools available for other operations. So they ran time tests on various materials, and found that the primitive diamond drills were much faster than modern drills run by machine. These drills also last a lot longer than commercially prepared drills.
So you can see, newer is not necessarily better, and the old drills probably last a LOT longer! The drilling time that they quote for a modern drill seems very accurate compared to my own experience. I’m sure that the reciprocating nature of the propulsion system is responsible not only for the speed of the drilling, but the longevity of the drill, as wear (or rather, the microscopic breakdown of the diamond surface) in one direction is reproduced immediately in the other direction, maintaining symmetry. I want a drill like this, as soon as I can figure out how to use it in a drill press!
I will jump from ancient history to the more modern uses of diamond. Al Gilbertson, in his book, ”American Cut”, describes the American diamond cutting scene, which started to take on an identity of its own around 1860. Although I am not addressing the actual cutting of gem diamonds, the book describes the brutal hand labor involved in “bruting”, or rounding out a rough diamond into the final shape, by rubbing two diamond crystals against each other, one the tool, one the gem. By hand. All day. Day after day. This was solved in 1873 by a man named Field, who patented an automatic bruting machine, where the stones were actually ground against each other mechanically. This was followed in 1876 with a similar patent by Isaac Hermann for a machine that is almost the same as those being used today.
Of course the progress of industry rested heavily on the back of diamond tools. As new ways were developed to shape them, new uses kept springing up.
Prior to World War II, diamonds were in use in dozens of industrial applications, including; drills, saws, excavation, measuring tools, watch bearings and parts, engravers, cutters, glass grinding, core drills, phonograph needles, lapidary, wire drawing dyes, aircraft systems, surgical blades, and the emerging field of electronics, among many others. In Idar-Oberstein, Germany, in 1935, there were 370 diamond cutting firms, with up to 25 employees each. Statistics from 1935 state that 75% of all diamonds were being used as tools or grit. When World War II began, diamond cutting became important to every war effort. The Germans put imprisoned diamond cutters in special camps, working on war machines, and scheduled special raids to secure inventory and supply lines. When the Russians invaded Germany, they abducted the Idar cutters to their own slave camps. Of course the Americans attracted as much of this talent as possible after the war to develop their own technological hierarchy.
In the 1950’s there was such a demand for industrial diamonds that scientists were predicting the exhaustion of all available supplies. Imagine, they’d be buying back every engagement ring in existence for saw blades and drill bits! Postwar diamond mining yields have averaged about 43% industrial stones to 57% jewelry goods. The statistics are not consistent, but current figures hover around those proportions.
Never fear, General Electric began trying to create synthetic diamonds, and by 1951 had achieved their preliminary success with peanut butter (The Diamond Makers, by Robert M. Hazen). Although the early crystals were no larger than 60 mesh size, and very friable, they were diamonds, and they were usable.
Friability is the tendency of a material to break down or crumble, and this property is very important in diamond tools. This characteristic is rare in natural rough, but General Electric, and ultimately all diamond synthesizers have been able to control friability as well as many other properties by varying the “recipe” for their stones. Adding various gases to the mix, scientists can control crystal formation and size, color, hardness, friability, electrical conductivity, and other properties of their product. Over the last 60 years, huge leaps have been made in the control over the crystals produced, and the products and prices have become stable.
Current information indicates that at least 90% of the industrial diamond today is synthetic, with more than 500,000,000 carats a year produced. Doug Klein of Eastwind Abrasives, a huge consumer and supplier of rough diamond estimates that practically all industrial diamond being consumed in the U.S.A. is man-made. China is a huge producer of synthetic diamond, and their process has improved tremendously over the years. With proper “micronizing” (regrading the micron sizing) it is very economical.
All indicators point to jewelry diamonds being safe from toolmakers for the foreseeable future.
USES OF DIAMOND
Diamonds are presently used in many modern applications. They are essential in many industries for their unique cutting, electronic, thermal, and abrasive properties. They are the hardest of all known materials therefore can be used to grind or shape anything. Some of the industries that rely on diamonds are; construction, mining, glass, semi-conductors and all aspects of electronics, lasers, medicine and dental, optical, concrete cutting, masonry and decorative tile and stonework, and of course, lapidary.
Historically, the single diamond crystal has been the classical diamond tool. Whether held in the hand or mounted in a drill or knife, this was the prototype. The original hand tools and current machines used to “brute” rough diamonds for gem cutting are examples. Single diamond tools are also used for dressing or shaping other cutting wheels. Until very recently, the single crystal cutter was a machine shop essential, with a small tetrahedral crystal wedged or welded into a cutter head.
One of the valued properties of diamond tools is not so much the hardness as the heat absorption. A diamond cutter can run almost non-stop, 24/7 without building up too much heat, thus quickly amortizing the $600 or so cost.
In 1951, before the advent of man-made diamonds in toolmaking, the qualities of diamonds for tools are described as: AA : clear, well shaped, brilliant, free of flaws, “fine”, or “select”; A : cloudy , minor flaws, blocky but not perfect shape, ”good”, or “regular”; Congo Grade : dull, included, encrusted, yellow or grey, “bort”. So the quality of the diamond is important for tools too, with better quality making a better, longer lasting, more expensive tool. Studies were done of the tool rotation relative to the crystal grain orientation, and the wear can be as much as 5 times as fast depending on this placement. Diamond tool making can be as demanding and precise as cutting them is.
Currently Chemical Vapor Deposition is a production technique for applying a diamond layer on cutter heads and other bladed tools such as scalpels and files. A hydrocarbon vapor is produced and energized under strict lab conditions and causes a very thin layer of diamond to be deposited on a substrate. The surfaces coated can be much larger and more flexible than those in other processes. Diamond windows were recently developed for an international fusion project called ITER that is being built in Cadarache, France. This window must transmit microwave beams and withstand a heat of 100,000,000 Kelvins. The Chemical Vapor Deposition window created from carbon vapor has aced all testing so far. The setup and operation of a CVD lab are much simpler and cheaper than for the High Pressure High Temperature (HPHT) method.
The HPHT method is the original method developed for creating synthetic diamonds. It is a “Superman” machine that crushes a chunk of graphite, using multiple hydraulic anvils, into a single diamond crystal. This process is being used for the creation of gem synthetics, but is not very cost effective for industrial qualities except where large single crystals are required.
Beginning in the 1990s Russian scientists began developing a method for producing diamonds called Detonation Synthesis. In this method, a block of iron is exploded with a ton of dynamite on each side, inside a containment chamber, usually under water. Each explosion results in about 1 kilo of diamonds. The resulting diamonds are embedded in iron slag, which is removed by boiling in nitric acid for a week. The resulting diamonds are “nano-crystalline”, harder than most diamonds, and very expensive for synthetics; as much as $5.00/ carat.
Most synthetic diamond ranges in price from 25 cents a carat to a few dollars, depending on the application, the type needed, and the quantity. Most of the cost of diamond tools is in the preparation and making of the tool itself.
The other forms of diamond that are in common use are loose powders and bonded surfaces. The applications for these in industry are plentiful; most drills, cutters, laps and saws being bonded; and loose powder or slurry are used in lapping procedures that are tiny and precise making processors, microchips, and silicon wafers; or huge and messy in quarries or masonry venues. I will expand more on these two procedures only as they apply to lapidary.
Bonded diamonds are any tools that have a cutting surface of diamonds. These tools are much more efficient than any of the applied powder tools because the grit is not replenished during use. It breaks down with use, and presents a new cutting surface as it wears, but new diamond is not applied as it is with slurry laps. The bonding can be done in a few different ways. The most common and reliable is electroplating. A layer of diamonds of a specific mesh is applied evenly to a flat lap (or other tool) and a thin coat of metal, generally nickel, is electroplated over the diamonds, fusing them to the base. This creates a flat, reliable cutting surface, the only downside being that they don’t last forever. As the diamonds break down, the mesh of the wheel becomes duller and duller, but eventually, rust and erosion start to peel the diamonds and plated surface off, and the tool must be retired. I can wear out about one such 1200 grit wheel per year. An 8 inch electroplated lap only contains about 5 ct. of diamond. Another form of bonding is brazing, or welding, the diamonds to the tool. This is usually done on drills, files, or carving tools, not laps, as the surface is somewhat irregular. These tools cut aggressively, but the layer of metal holding the diamond eventually wears through and the tool is history.
Resin bond is the application of diamonds in a polymer or resin layer on the top of a lap, belt, or tool. For faceting, resin is not acceptable, as it is too soft to cut absolutely flat surfaces, but resin bond is a great way to go for cabbing wheels. Regular flat or horizontal wheels are made with resin bonded diamonds for some of the fastest and smoothest cabbing machines ever. The lifespan of a resin bonded diamond wheel is epic. Resin bonding is also used on pads, belts, and fabric discs for polishing, up to1/2 micron (50,000 grit).
Sintering has traditionally been the king of all diamond tool making. In this process, diamond powder is concentrated in a layer of metal based compound that comprises the top portion of a lap, or outside of a tool. This compound is usually a proprietary formula or process, but the result is a very durable lap that cuts fast and smoothly for years. The sintered layer is like having a solid diamond wheel, and if used and maintained carefully will last almost forever. Almost all diamond saw blades are bonded, with a coarse mesh diamond either plated or sintered along the edge of a metal disc. The sintered blades are the best on the market, and last much longer.
The final and oldest form of bonding is surface bonding, in which the diamond is applied to and pressed into the surface of a lap, usually copper. I actually made a wheel like this for this Symposium, and my only regret is that I waited so long to do it. This type of wheel will last practically forever, as a small reapplication of diamond powder will give many dozen stones worth of cutting power. It is not prone to peeling or rusting like the electroplated laps. This process is very good for 600 grit or finer laps, but lacks the aggression for a preforming wheel. The making of a copper lap with the surface bond process is described and illustrated very clearly by John Sinkankas in Gem Cutting. I chose to make a 1200 grit wheel because that is what I use the most. After a very short breaking in period, it cuts quickly and smoothly, needing more diamond about every 50 stones. The original application was 5 carats (I should have read Sinkankas more closely, he recommends 2), and subsequent applications have been about 1 ct. Even though olive oil is used while impregnating the lap, I cut with a light water drip and it is not messy.
Applied diamond polish can be used with a manufactured paste or homemade slurry on a variety of surfaces. For faceting, I stick to a zinc or ceramic lap and use ½ micron (50,000 mesh) for polishing. I keep a 50,000 and a 100,000 mesh ceramic lap clean and available for extreme circumstances. For cabbing, I will use diamond pads for most sanding steps, and paste on felt wheels or polypads for polishing. When carving, home made diamond slurry is used at every step after the initial carving. Sanding starts with 240 mesh diamond powder mixed into mint gel toothpaste, and extended with water. Really! The viscosity is very controllable by adding or withholding water. And it smells good! This is applied to various surfaces such as felt wheels or bamboo points to remove tool marks in the first step of the sanding/polishing phase of carving. The mesh steps vary according to material, but all subsequent sanding and polishing is done in a similar manner, with the gem and the work area being completely cleaned between each grit stage.
All diamond tools in a lapidary setting are used with a liberal supply of coolant, usually water, running over the working surfaces to lubricate and cool everything. Large rock saws and some large tools are lubricated with an oil bath.
Diamonds are separated into mesh sizes for the various needs of the consumer. Specifically, a mesh size indicates how many particles of a material will fit through a screen with a certain number of holes per square inch. So 60 grit is very large, coarse particles, appropriate for very rough grinding. Grits are screened through progressively smaller screens to achieve “mesh” separation. Every grit, or mesh, size has a micron equivalent. A micron is .001 millimeter and diamond grit is sorted into micron “ranges”, which include allowable variations in size. Powder graded as 15 micron is actually between 10-20 micron in actual size. This shouldn’t matter in any lapidary applications, but it is good to know what the reality is. There are many mesh/micron charts available, and many disagree. I learned that the actual micron or grit count in a diamond product can often be closely guarded proprietary information. The chart below carries the most widely available ranges used in most products. The following chart was provided by Eastwind Lapidary and contains all the relevant data to compare micron and mesh equivalents. As you can see, some of the figures are from the U.S. Bureau of Standards.The most common and accepted standard for micron/mesh is the FIFA Standard, from Europe.
In grinding procedures, if one had a very large, tough stone to cut (say a 500ct. quartz), the grinding steps would be 100 mesh, followed by 240, 600, 1200, 3,000, and on to the final polish, which would be 50,000. Not all cutting uses each of these steps, with most precious gems being started on a 1200 mesh lap and going straight to polish. Diamonds are only used for polishing the hardest of faceted stones, sapphire and sometimes spinel and chrysoberyl. This diamond mesh is used in a paste or spray, commercially available, or loose powder applied by hand with a little lubricant. Most faceters prefer to use a softer alumina powder, “Linde A”, ½ micron, for most other stones. Cabs have to visit more of the required steps to achieve perfection, as do carvings. I personally use only diamond tools and polishing compounds on all my carvings. It allows good control during every step of the process.
In addition to size, synthetic diamond grit is available in two types; friable, or polycrystalline; and metal bond, or monocrystalline. There are wide ranges of properties available in each category. The friable grit is created in tiny crystalline groupings which break away during use, constantly forming a new cutting surface. Friable diamond is used in loose diamond applications such as carving and slurry work during lapping. Metal bond diamond is grown in monocrystalline form, and the crystals remain intact during wear. This is used for bonding, plating, and sintering tools. Minute octahedra are visible under magnification, and in the polycrystalline material, tiny clustered crystal groupings are visible.
In closing, I’d like to say that the history of diamonds begins with tools, and follows parallel paths with gems and tools, until the mid twentieth century. Then the paths diverge as much as is possible, with the path of diamond tools swinging directly toward synthetic diamonds. Essentially the entire future (and what a huge one it is) of diamond tools is about how man has set about reproducing and isolating the unique properties of diamonds for more and more sophisticated means of (hopefully) improving his life.