Boris Kolodny, B.A., M.A., F.C.G.M.A. and (name of my co-author has been removed by his request) January 10, 2012.
Many of us choose rough without thinking of designs and wonder later on about how to cut the material. What shape should we use? Will the selected shape accommodate to the rough? What kind of return will we get from our purchase? While the answers to these questions are rarely straightforward, our presentation this evening relates to correlating designs with rough gemstones.
The range of shapes one can cut stones into is quite wide. We’ve included a group taken from the DataVue collection: Index to Facet Designs: Shape Classification List. There are forty-six shapes and thousands of designs available both within and without DataVue. Some years ago, Michelle Heath presented a description of Free-Form and Fantasy Cuts, allowing many more choices. However, tonight we will look at samples of the rough you brought in and we’ll consider the alternative cuts available for each. Hopefully, after we have shared ideas, we’ll all go home with a better idea of our choices when we look at a piece of rough.
In the January Newsletter, Bill very thoughtfully included an article by Howard R. Bromley, How Much Rough Do I Need? The writer explains how one can choose a design and then estimate the size and shape of the rough needed.
When buying rough material, one needs to consider many criteria, all ready discussed during earlier meetings:
n kind of material
n cleavage plane(s)
n colour and colour zoning
n doubling of facets
n orientation of the crystal axes.
These aspects must be considered when selecting a design to cut.
GemCad is a most helpful tool!
- Each diagram has several measurements included enabling one to make a decision about what design will give an optimal return on your rough.
- L/W, H/W, U.W, P/W, C/W and Vol. /W3 = ?1
The latter notation means that the volume of the stone divided by the cube of the width of the stone is equal to a figure, for example, 0.279. [The cube of a number is the number multiplied by itself three times.] The volume fraction can be used to estimate the carat yield of a finished cut.
The width of the stone is shown on the GemCad screen and measured either horizontally or vertically when viewed from the top, whichever is smaller. To use the volume fraction to estimate carat weight, measure the width with a caliper in centimeters (mm/10), cube the measurement and multiply the result by the specific gravity of the material in g/cc in turn multiplied by the number for the volume fraction Volume/Width cubed given by GemCad. The result will estimate the weight of the stone in grams. Multiply by 5 to determine the weight in carats.
Width (mm/10) x W x W x Specific Gravity (g/cc) x Volume = Weight in grams x 5 = Carat weight
For example, let’s compute the weight of a 12 mm wide piece of quartz with Volume/W3= 0.279. Noting that quartz has a specific gravity of 2.65 g/cc, and 12mm = 1.2cm
Weight = 1.2 x 1.2 x 1.2 x 2.65 x 0.279 = 1.28 grams x 5 = 6.39 carats
If you prefer, you can use millimeters instead of centimeters; the weight will come out in milligrams. You then divide by 200 to get the weight in carats. Using the figures above,
Weight = 12 x 12 x 12 x 2.65 x 0.279 = 1280 mg / 200 = 6.39 carats
Note that the volume fraction depends on the actual girdle thickness shown in the diagram, so it will vary with the girdle thickness shown on the screen.
- Use the C command in Gem Cad to round off the indices.
The above calculations are simplified in a downloadable program written by Gary Kratochvil: Gem Weight Estimator.
- 70 % of the Width will give you the estimated Height (depth) of the stone. A 5 mm stone will have a depth of 3.5 mm.
- This is particularly important when cutting dark material such as dark Blue Sapphires.
Important Factors to Consider When Selecting Which Design to Use:
Make sure to have available: white paper, micrometer or calipers to measure various dmensions. Some designs by A. Wolkonsky for example, often measure across the corners of the stone (sharp cornered stones) in order to obtain the exact size.
Other helpful instruments which were shared during the evening included:
- A map grid originally made by the Canada Map Company with which one can examine the dimensions of a piece of rough and get an idea of possible cutting shapes.
- A lever-based protractor allowing consideration of a variety of shapes.
When examining gemstone rough, find the C-axis of the material to determine doubling of the facets perpendicular to it. Examples include: Peridot, an extreme case, or Kyanite.
Color is important in dealing with tanzanite.
Consider a choice of design in terms of its use in jewelry. Remember that deep stones are not easy to design for, or set in jewelry.
One possible approach is to measure the rough and draw it on a piece of paper. Determine the critical angle. One can then estimate crown and pavilion angles and determine if the rough is suitable for your design.2
Return on rough3 based on the shape of the selected design:
ROUND BRILLIANT – 24%
OVAL – 33%
MARQUISE – 15%
PEAR – 13+%
SQ. STEP – 40%
EMERALD – 33%
The Round Brilliant is one of the more wasteful of material of all the designs.
With the Emerald Cut one needs to dispense with the normal rules of centering your stone or cutting at a set platform height:
When performing an emerald cut on high priced material first, cut one side of the crystal mirror image and on the opposite side one may have to measure the width of the facets in order to obtain the greatest return on your rough. Facet an even girdle to facilitate cutting an Emerald Design.
The bow-tie effect is frequent especially in Marquise Cuts; if the L:W ratio is greater than 20% or 1:1.2 that effect will be more visible. The same result will be more pronounced in barion designs.
The remainder of the evening was devoted to examination of the rough material brought in by members. We realized a number of things as members of the group helped each other with design choices or were assisted by the authors.
– It is helpful to have a good three-dimensional perspective when regarding stone and rough.
– We rarely found suitable shapes without consideration of the items noted above when buying rough, i.e., inclusions, color zoning, fractures, cleavage, crystal orientation, etc.
Thus, a tablet (flattish) piece of beautifully colored ruby required dispensing with the traditional design in favor of a table surrounded by a hexagonal cut single set of facets highlighting it.
A fine piece of pale salmon-colored sunstone was considered in favor of color, not schiller and some optional designs were recognized.
A large piece of citrine offered a material-sparing pear cut rather than a more wasteful (based on the shape of the stone) standard round brilliant design.
Some fine tourmaline invited emerald cuts with consideration of the light and dark c-axial view.
The authors wish to express their heartfelt thanks to Al Manestar for his help and guidance in preparing this presentation.
List of Works Consulted
1. Strickland, Robert W. (1992). GemCad User’s Manual. The Diagram Menu. Version 4.51.
2. Giesbrecht, Robert. Email to Faceters’ Digest. April 24, 2002.
3. Goodger, Don. Personal Communication, 1989.
By Boris Kolodny BA, MA, FCGMA Feb.15.2013
In preparing for this talk I decided to talk first about problems encountered in cutting Tourmalines mainly because I was in the middle of cutting a lovely green Tourmaline. In the process I encountered all of the problems that one would expect. It must have been fated for me to add this to the talk.
In the case of the stone, please see pictures in this article, I had to deal with several issues.
I receive a call from a young woman who told me that she collects gems. She had recently purchased a bi-color Tourmaline crustal which is rather large and she wanted to have it cut. Normally, when we cutters say bi-color, we mean that the stone will have two colors evenly distributed on either side of the dividing line. Mostly that applies to green and pink colors.
When the woman brought the stone to my shop I found out that it was not the case with her stone. Because she did not have enough experience she had purchased a stone which was rather large but it was mostly pleasant pink in color and only a small part on one end was green.
Now I was faced with a dilemma as to how to orient the stone. I did not want to lose too much material and cut the largest stone I could from the material. On the other hand there was the issue of the color.
I decided to ct it as it was and get the colors mixed through the process of internal reflection. The green color form one end would reflect into the stone and will mix inside of it with the pink. Unfortunately, there was a very large a deep inclusion at the bottom of the crystal which I decided to cut out. In spite of all that the stone turned out to be large, over 6 carats, and very lovely mixed color which were very pleasing to the eye. The customer was very pleased and I was satisfied.
First of all, let me say that the problems encountered in cutting Tourmalines are not unique to them only. These problems can be found with a variety of other gem materials. However, they are unique in the sense that these problems are encountered while cutting Tourmalines 95% of the time. That has been my experience, anyway.
In order to understand what I am talking about we will need to define the terms first.
The unique problems found with Tourmalines are that when cutting them the directional hardness will suddenly change in the middle of the cut in a fraction of a second. You will be cutting a stone and everything seems to go very well. You have cut a couple of the facets without any problems and you think that you are almost home free and all is well. Low and behold, the facet suddenly takes a detour and goes off to one side or another, without any regard for the direction that the machine is set to go in or the dial indicator! The stone suddenly decided that it does not like the direction that you want to go in and it chooses its own direction. In street parlance we call it being screwed!
Normally, the facets in a step cut would be parallel to one another. However, in this case some facets were not very cooperative and gave me much grief. They were al over the place. One would go up on the right side and the other one on the left side. There was no rhyme or reason to how it behaved. That is very common how it happens.
So, be prepared, and try to use a finer lap for cutting so that you do not cutoff too much and leave yourself some room for error.
I have brought a sample stone here with me that had done exactly that to me. As you will see from this example is the fact that you have been a cutter of some standing in our cutting community does not exempt one from experiencing the same amount of grief while cutting.
Fig. 1, Bottom directional hardness problem
In this talk I would also like to address a few other issues.
One has to do with a color concentration in a particular spot in piece of material.
The other issue has to do with actual zoning. These are most often are associated with the growth line in the material when it was formed.
Fig. 1a, color concentration in spots
Each issue is managed differently.
Before I go on discussing the topics I would like to remind you that any work done by a faceter requires much patience, time and dedication. It is mostly a lonely work but it has its rewards. To me personally, it provides lots of time for reflection and meditation. And, it will keep the Alzheimer’s away for a long time. I would encourage my fellow factors not to shy away from a task because it may be difficult. Experience comes only from practice. And, if you want to become a good cutter you will need to do it and do it often.
It needs to be understood that whenever we deal with a colored material there will inevitably be variations in color intensity. That as a rule does not present much of a problem since when the stone is cut the color will blend in nicely in the finished stone.
However, if we are dealing with a piece of material that has a single spot of color we need to handle it differently. If you are at all familiar with how the light behaves in a cut stone it will stand to reason to place the spot of the most color at the culet of the stone. When finished, the stone will be flooded with color all over. The best cut for such material is usually step cut or an emerald cut or something that is a variation of that.
Fig.3, Finished stone, Bi-color Tourmaline
In the event that we are dealing with a band of color, it will have to be placed parallel to the table of the stone inside the pavilion. This also the case when cutting stones with a twining plane, please see fig.1below. Some may create a barrier for the transmission of light and others will reflect the light under right angle. These are best positioned with the twining placed parallel to the table inside the pavilion and the crown. Care must be taken when cutting such stones as the twin can split suddenly without warning along the line of the contact of the twins.
Material that is known for its problems with cleavage must be properly oriented prior to cutting. One known example is Topaz which has perfect cleavage. It is parallel to the crystal base and must be oriented away from it when determining where the table will be. Some cutters will create a specially ground dop at 12.5 degrees which they will use only for cutting Topaz.
Stones with single or multiple cleavage planes need to be cut and polished with much care
It may be necessary to often reverse the rotation of the pre-polishing or the polishing lap. And, the speed may have to be slowed down considerably. This, of course, will slow the entire process of completing the task. Sometimes the softest lap available should be used.
Often zoning can be explored to enhance the appearance of the cut through clever location of the zoning in the stone. This can be very attractive. It is worth while experimenting with possibilities. This is the case with much of the Amethyst that comes from Thunder Bay.
Kunzite is another material worthwhile mentioning. It needs to be oriented for color with the table on C axis. It also can shatter while cutting especially if the gem was subjected to grinding. A word of caution is in order here, if you are planning to cut Kunzite make sure that should it is sawn only with a new diamond blade and anything that needs to be removed should be done so with the prior to cutting. And, avoid grinding as your stone may just shatter in the process of faceting.
And, there is no substitute for experience. The more you cut the more you lean about properties of various gem materials.
List of works consulted:
- Glenn & Martha Vargas – Faceting for Amateurs, second edition, revised.
- My own notes and experience
- Drawings are courtesy of Glen and Martha Vargas books.
Do-it-yourself tips from a gem cutter who’s figured out how to shoot stones and still have time and money to cut others.
By Boris Kolodny, BA, MA, F.C.Gm.A.
All photographs are by the author.
If you’re a gem cutter, sooner or later you’re going to decide to photograph your gems. Maybe you want to catalog them, maybe you want to sell them, or maybe you simply want to brag before lesser folks. So you pull out your camera and get to work. You look at the results — and that moment, you discover that the picture that is supposed to be worth a thousand words doesn’t look anything like the stone itself! The stone is bright, rich, and lively, but the image is dull, dark and lifeless. You try this, that, and the other, but the outcome is the same and the task seems impossible. It’s not!
You can take a photo of your gem so that it looks the way you know it should. All you need are the right tools and the knowledge of how to use them. So let’s begin with a good camera and proper lighting.
I’ve found that it’s possible to obtain equally good pictures with either a “regular” film or a digital camera. The better the quality of the camera, the better the picture produced, and fortunately, in today’s market you don’t need to break the bank to buy a decent camera.
I’ve been so pleased with my digital that I’ve completely switched from my film Nikon F2 to shooting all digital, and many of my points here relate to digital photography. I find that a digital camera provides more versatility and greater ease of operation. A great plus is that you can immediately see the results, and if you’re not satisfied simply delete the picture and do it over until you are satisfied.
Other useful features include Email Mode, choice of Resolution, Shutter Priority to select a shutter speed such as 1/8, 1/15, 1/30, and so on, Aperture Priority (settings include F2.8, F3.4, etc.), and Macro Mode. The last feature alone will save you a considerable amount of money since you’ll no longer need to buy a special macro lens for close-up photography. (I’m referring to these features as they are named for the Sony Cyber-Shot, the camera I used at first, though now I use a Nikon D70S, SLR; most digital cameras use the same or very similar terminology.)
It’s also easy to increase or decrease exposure as required in the manual mode; the instructions are in your camera manual. Another benefit is that you can immediately upload your pictures onto your computer and print them yourself on a color printer with considerable savings. I find that the newer digital cameras that have a see-through-lens viewfinder are easier to use than the LCD screens, which are hard to read in a bright light. The resolution is of some importance and will depend entirely on your personal needs and what you intend to do with the photograph afterwards.
Some of the choices on the market today are Sony Cyber-Shot, several Nikon models, Minolta, Canon, and Olympus. As with any kind of electronic equipment today, new developments are constantly in the works.
The setup will require a background of your choice. Some cutters prefer their gems photographed on a black background, others on white. Black will highlight any design on the pavilion. Consider how you want the gem to appear. Do you want to accentuate the transparency, color, brilliance, or some other feature? This will require some experimentation on your part. The typical setup will require a light, a camera, and a tripod.
My preference is to set up a light on each side, at equal distance from the center and at each at 45 degrees to the other in order to cancel out reflection.
Perhaps as a cutter I’m biased on this next point, but most of us would agree that the most important element in gem photography is the gem itself, and the issue of how to set the gem up is critical. I’m sure that everyone struggles with getting the gem to sit properly. I find that a simple gem stand works just fine. Another simple solution is to use one of the gem sorting trays that you can often pick up from gem dealers. The grooves in these trays, made just for placing gems for display, are perfect for holding a gem while it’s being photographed.
A simple gem stand works well in setting the gem up for a shoot. You can use white or black material for the seat.
For me, the Auto Mode works best. The camera does a good job on Auto Focus. I set my camera on the highest resolution possible, and the picture quality on Fine. (Please consult you own camera manual for comparable settings.)
If you use the Aperture Priority option on your camera, you will do well to set your aperture to the smallest opening, which is F8. A good time exposure would be 1/3 sec (second). F8 will provide the greatest depth of field for our purpose. Note that Aperture and Shutter Priorities are available only in Manual Mode; all higher-end digital cameras have a manual mode. You will find that you must bring the lens of the camera very close to the gem — how close you can come will depend on the capabilities of your camera. I photograph as close as 3-1/4 inches. You can shorten the distance as well as enlarge the picture by using a lens magnifier, which can be found in any photo store. Make sure the one you purchase has good quality optics and fits the lens on your camera, as magnifiers come in different sizes.
Film cameras used to come with separate release cables, which would eliminate any shaking, but digitals don’t come with these. SLR cameras are the exception. I get around this problem by using time release, a feature every camera should have. All you have to do is to set up your shot to your satisfaction and set the function on time release. Next, press the button and let the camera do its thing. Ten seconds later it will take the picture just the way you set it up.
As in any photo shoot, getting the lighting right can be problematic. Some people favor the use of a flash. However, I find that it’s better to use uniform lighting because it eliminates any hot spots or whiteouts.
Over the years I’ve tried to build something similar but withoutany success. Cloud Dome is very well made, the plastic is just the right color, and best of all, it works!.
The Cloud Dome comes complete, including the dome itself, which eliminates bright spots or reflections, as well as all the stands and pads you’ll need, a couple of color-corrected and temperature-balanced fluorescent lights, a reflector, extensions for the dome, background, mounting brackets for both regular and digital cameras, and a nicely designed bag in which all the mentioned items nicely fit. The price is about $500 (U.S., as of 2005) — a bit steep, but well worth it for having solved a lot of my problems. I’ve been using it with great success and ease for a while, and it’s helped me produce photographs that do my gems justice. But judge for yourself!
With the light set up as described above, you’ll need to experiment with some individual stones, since each behaves differently in the light. Cloud Dome takes a lot of the guesswork out of lighting, though, and you may find that you don’t need as much light as you may have believed. Because your camera is mounted on a stationary bracket, once you’ve determined the optimum location for your stone under the dome, you can use it for all the other stones, though some minor corrections may be required.
Shown are just a few samples of what you can do with the set I’ve described. Please bear in mind that any color correction, cropping, or other modifications can easily be made with Photoshop. For many stones, though, getting the color right is quite problematic. (I’ve had problems with light or colorless stones, Rubies, some Garnets, Alexandrite’s red and green, all the nuances of color in Andalusite that your eye sees, Imperial topaz, Cherry topaz, opaque stones, Opal, and especially Fire Opal.)
Using a light box allows me to provide light from the bottom of the stone, which I find necessary with very dark stones such as dark-green Tourmaline or dark Amethyst. I constructed my own simple light box which is easy and inexpensive to make (total cost, about $10).
The box measures 3-5/8 inches high, 11-1/2 inches long, and 10 inches wide. To make it, I visited a surplus store and there purchased a metal cover from an electronic unit with three open sides, two of which are vented. Venting is important since there is heat buildup from the lights during operation.
I used two pieces of non-transparent plastic to cover the sides. I cut an opening into one of the sidepieces to fit one of the fluorescent lights. I believe it is the best way to go, as the light is already color- and temperature-corrected. On top, I placed a piece of milky white polyethylene plastic. You can also use any other plastic as long as it is translucent.
Everything is put together with small wood screws. I recommend that you first drill pilot holes for these, using a drill bit that is smaller in diameter than the screws.
I found that the best way to use this setup is by placing the light in the back of the light table. If you try to place the light in front, it will get in the way of your camera.
If you’re using a film camera, you need to consider a few other things. Here’s a brief rundown of them.
For a lens, you’ll need a macro lens, probably, a 35 to 60 mm. Try to get a fast lens if possible.
For film, watch out for the grain effect! The lower the ASA, the smaller is the grain. I discovered that 64 ASA resulted in the smallest grain.
Slides or prints? Slides seem to work the best.
As for light, if you’re using tungsten bulbs (your everyday bulb), it’s best to use tungsten film or slides as well. My preference (when I still used film) was Kodachrome 64 ASA, used with daylight lamps.
(Make sure you set your depth of field to the optimum. This will allow you to see the entire stone without any part out of focus.)
AND KEEP IT CLEAN!
This last point is very important, and should be one of the first and last things you attend to. Make sure to clean your stones very thoroughly before photographing them. I use a brush with a blower that is used for cleaning camera lenses as well as a good, lint-free, stone-cleaning cloth. If you’ve never tried to photograph your gems before, you might be surprised at how a little speck of lint will seem as big as an elephant in a close-up! u
Boris Kolodny is a gem cutter, jewelry designer, fellow of the Canadian Gemological Association, and a member of the North York Faceting Guild and the U.S. Board of Trade. He has acquired intimate knowledge of gems in over 40 years of experience in jewelry design and manufacture. He can be contacted through his business, Artistic Jewelry Design, or via his Web site at www.artisticjewelrydesign.com.