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Carl M. Unruh, Intermountain Faceters Guild
INTRODUCTION
Cubic zirconia, CZ, is a great faceting material. Today, it is reasonably priced. That has not always been the case. If you were a faceter in the early 1970’s, you will probably remember the first cubic zirconia you ever purchased. Some of us have some, which we paid so much for, that we have not yet faceted it. The first piece I purchased was at a Spokane WA show in the early 70’s. The price was $3.50 per carat, and when one puts a piece on the scale, the carats really run up fast. WOW, 10 carats cost me $35. Today, except for some special colors, green namely, one can buy CZ for about 5 cents per carat. While that will still add up quickly, it is a very reasonable price considering the manufacturing steps and process.
CZ is made by melting zirconium oxide with another metal oxide, usually calcium oxide. The melting temperature is very high–4,982°F. Now, there are no containers that can be heated to that temperature without melting themselves. So, what is one to do? The method used is called “the skull-melt process”. The zirconium oxide is heated by radio waves, but the container is water cooled. This results in a layer of the zirconium oxide powder next to the container that keeps it from melting while the zirconium oxide in the center melts. Upon cooling, the zirconium oxide melt forms an irregular crystal in the middle with the unmelted powder all around it. You will never see rough CZ shaped like laser ruby.
The manufacturers have a lot of leeway. They add about 10% calcium oxide to ensure a cubic crystal formation, but the more calcium oxide they add, the lower the melting point, the cheaper the material cost, and the lower the hardness of the CZ. I have felt that the CZ we buy today is not as hard as what we bought ten years ago, but who knows, I may just be more used to faceting CZ now than years ago.
PROPERTIES
CZ is zirconium dioxide with about 10% yttrium oxide or 10% calcium oxide added. It is cubic with an R.I. of 2.15 to 2.18. It is singly refractive with a hardness of 8 to 8.5. It has a slight anisotropy in hardness. It has a specific gravity of 5.6 to 6.0 and, while somewhat brittle, it has good durability. To me, CZ it is a much better diamond substitute than the newly marketed Moissanite, especially since the Moissanite is not even cubic. So, with Moissanite there is always a direction of facet doubling.
The table below presents some of the comparisons. Check it over and draw your own conclusions. In all optical properties, CZ is closer to diamond than is Moissanite.
| Properties — Diamond, Moissanite, CZ | ||||||
| MATERIAL | HARDNESS | TOUGHNESS | R.I. | BIREFRINGENCE | DISPERSION | S.G. |
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| DIAMOND | 10.0 | EXCELLENT | 2.417 | NONE | 0.044 | 3.52 |
| MO1SSANITE | 9.25 | EXCELLENT | 2.648 2.691 |
0.043 | 0.104 | 3.22 |
| DIFERENCE FROM DIAMOND |
0.75 | NONE | 0.28 | 0.043 | 0.060 | 0.30 |
| CZ | 8.25 | GOOD | 2.165 | NONE | 0.062 | 5.58 |
| DIFERENCE FROM DIAMOND |
1.75 | SLIGHT | 0.25 | NONE | 0.018 | 2.06 |
One occasionally disturbing property of CZ is the appearance of striations down the long direction of the crystal. These are observable in most gems cut as rectangles or squares and having a dimension of an inch or more. They are clearly visible in the Countess, but don’t show up in the picture on the cover of this pamphlet. For small gems, one would need to look hard to see them.
These days, CZ can be obtained in essentially every color, although the greens and a few other special colors will sell for a premium price. Be careful of the dark colors CZ. Often the darker colors like blue, red, or even amethyst color can just be too dark to be brilliant. If you want to facet these darker colors, think about faceting small gems, say about 8 mm..
DOPPING
CZ is not heat sensitive, so one can dop without difficulty. I like to grind a flat area to dop to. Use a rather coarse lap, 180 or so. Always use as large a dop as can be attached to the gem. This provides more gripping area and helps prevent losing a gem off the dop. Get the piece of CZ hot enough to cause the wax to “wet” the surface of both the CZ and the dop. Hold the two together until the wax sets up well. Using a clamp and small jig to hold the gem and dop without movement is always recommended. I think that movement while dop wax is setting up is a frequent cause of dopping problems. I dop only with wax, so cannot advise you on the glues.
CZ COLORS
Many of the colors of CZ are shown here. I don’t have them all, but this will give you a good idea of what is available.
GRINDING
CZ GRINDS NICELY. There is very little variation of hardness with different directions or angles. It may show a different texture even across a given facet face and may look like it will surely fracture or fall apart. In my experience, I have never had one actually separate, although on some of the 1000+ carat gems, the look had me very worried. Grind pavilion mains at 42° to 43°.
FOR GEMS UNDER 15 MM
For gems to finish out at about 15 mm or less, grind initially with a 260-grit lap. Grind in all but the smallest facets. Next grind all facets to good meets with a 1200-grit lap. Many of us like to “ROLL OUR OWN”. We roll 1200 diamond powder into a copper lap. Sprinkle diamond powder on a lap slightly wet with Kerosene or very light oil. Use about 4 or 5 flat toothpicks full of the diamond powder per charge. The diamond can be ROLLED in with an old bearing, a piece of laser ruby, or even the side of a glass jar. If you ROLL YOUR OWN, you always have a sharp lap that gives a smooth and fast grind. I have noticed, all too often, that an old metal-bonded 1200 lap will produce scratches that can be a real polishing problem. If copper laps are not available, one can add 1200 diamond to a type-metal or even tin lap. These last two combinations will require more frequent recharging but will produce a very smooth grind.
Charging your own metal lap is rather easy. I like to do it a bit removed from my faceting area so as not to contaminate anything.
Never use a “charger” used for a larger grit for a finer grit. I keep chargers in separate freezer bags (but not in the freezer). Wash your hands well after charging!
FOR GEMS OVER 15 MM
The bigger the rough, the larger the grit used for the first grinding. I commonly start with a 100-grit diamond lap. Use this just to rough in the main facets and the rough shaping of the girdle. A 100-grit lap will leave BIG DAMAGE to the rough, but it will remove material quickly so that you can get down to the actual faceting. Any sharp corner will be severely damaged by a 100-grit lap. Corners on square gems will have big chips as will the culet, especially on any emerald-shaped gem. So the real message is, use a really rough lap to get the rough-to-basic shape; but DON’T GO TOO FAR!
After the 100-grit grind, go to a 260 lap. A 260 lap is nice because it can remove material pretty fast and still leave a fine surface roughness. After cutting all the facets except the very small ones, go to a 1200 lap. If your gem is over 15 mm, then lots of time and irritation may be avoided by recutting all the facets with a 3000-or 4000-grit lap. Your gem after grinding with 3000 or 4000 diamond will look pretty well polished, but don’t quit just yet! It can and should be better.
At each change of grit size, it is most important to grind away all the damage left by the previous grinding. That leftover damage can amount to quite a lot. Note the depth of the damage layer that should be removed depending on the grit size used. Be sure to grind long enough to remove the damage from the previous lap.
FOR ALL GEMS
Cleanliness is always important in faceting. Try to avoid letting any solutions run down the dop and into the collet while grinding. These surely may reappear during polishing and, Wow, unexplained, unwanted, and troublesome scratches can result. Also, clean the gem by wiping with a wet Kleenex or similar wipe when changing from one lap grit to another.
POLISHING
CZ with a hardness of 8 to 8.5 is best polished with diamond. I’ve had no luck with chemical polishing compound. I like to score my polishing laps, but only very lightly with a shape knife.
Now think about this–the diamond grit size one uses to polish CZ or anything else depends on the quality of polish you require and the LAP USED FOR POLISHING. It took me a long time to realize this.
You can rather quickly polish CZ gems 15 mm and smaller with 100,000 diamond on tin. For larger gems, the 100,000 on tin is very good but very slow. Lately, I have used 50,000 on tin and can’t see any difference. Also important, is what coolant is being used. Well, for many a year I used the old original standby, Kerosene. A very few drops at a time, just to keep the lap wet. I also use a slow speed. The last few years, many of us in the Northwest switched from Kerosene to SLIDE TROMBONE OIL. Strange, yes, but think about it a bit. Trombone oil is highly refined, a very light oil, and is essentially odorless–a big advantage if you facet near you living area. You can buy the trombone oil at most musical instrument stores. If one uses Kerosene, trombone oil, or even water, the next task is to wipe the facet CLEAN so that the surface can be examined. If you can’t see it, you cannot be sure it’s polished The best cleaner for this is chamois skin or split deer hide. A few square inches will go a long way, and it does a very thorough and fast job of cleaning a facet with next to no effort. You should really give it a try Liquid from a slightly damp facet will “fill” scratches and give a facet a polished appearance that won’t be there when dry.
A harder lap works a bit better for the 100,000 grit; try type-metal. There is an amazing difference in speed between tin and type-metal with 100,000 for CZ. Also, don’t forget that the quality of the diamond grading can make a huge difference in overall polishing quality.
There are many more polishing laps available and many faceters have good success with them. I’m not one of them. Seems to me, that when I find a system that works, I’ll stick with it. Now I have tried the others because one can always learn new things, and I sure recommend “new” but only when it has some advantage. It seems to me that a lot of new things are more properly called “different” and may be no better than “old”.
For CZ, I have tried many different polishing laps. I’ve had two different ceramic laps, but what a pain to make them work. I’ve also had two different LAST LAPS, but no great luck with them. The Corian laps did not work for me. I even have the bronze lap. I now use it with 1200 grit for grinding.
A lap I have used and like a lot is Kerksite, but I know of nowhere one can be purchased. Mine was specially made by a good friend. If you ever see a lap of this material, buy it. It will polish CZ in good order.
A new CZ polishing lap of interest is the Blue Casting wax lap. They are run at rather high speed and used with 3000-to 4000-grit diamond to produce a great polish. The soft lap makes it possible to polish with this grit.
The new BATT Lap is also interesting, but I need more experience with it to decide its overall value. Many have used and liked the BATT lap and recommend it.
I believe the best bet for a flawless and fast polish on CZ is to do a prepolish grinding with each finer grit to be sure to remove the damage from the previous lap. Finish off the grinding process with 3000-or 4000-grit diamond.
For polishing, one cannot beat the tin lap or the type-metal lap. You may have noticed I did not mention the diamond paste syringes for applying diamond grit or polishing compound. Well, I never had confidence in them. Seems some had adequate diamond and some did not. By using the pure diamond powder, one always knows just how much diamond is being applied.
Diamond powder is hard to beat in price and performance. Find a quality diamond powder supplier and stick with them. I have bought miscellaneous diamond powder from various dealers because of a low price, only to later discover the low price was due to poor quality size grading or contamination. There is a big difference in diamond powder quality. Diamond powders of a given grit size really contain a range of grit sizes. Some grade with a wider range of grits in a given size than others. It is always good to get a small range when looking for diamond grit for polishing. Of course, for the rougher diamond grits, this is usually not important.
SUMMARY
- CZ is great faceting material. Good diamond “look-a-like”.
- Choose the lighter colors for brilliant gems; for dark colors, facet small gems.
- Preform gems 15 mm or smaller with 260-grit laps. Final grind with 1200 grit.
- Preform large gems, 15 mm and more with 100-or 180-grit laps. Final grind with 3000 or 4000 grit.
- Always grind deep enough to remove the damage from the previous grit.
- Polish with 100,000 grit on type-metal or 50,000 on tin.
- Clean facets with chamois skin to better see facet surfaces.
- Remember the 3 “F’s”, Facet For Fun!
Great CZ Cuts
The next section features some great CZ designs. Although the diagrams say R.I. 1.54 or so, I have found the angles in the diagrams produce some very bright gems. Of course, feel free to change the angles to your liking. Have some faceting fun!
If you have Data View and GemCad, you can just run them directly from those programs. “Millennium” is the only one not yet in those programs.
MILLENNIUM
| GemCad Ray Traces for RI = 1.54 | ||
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| Random Model | Cosine Model | ISO Model |
| GemCad Ray Traces for RI = 2.16 | ||
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| Random Model | Cosine Model | ISO Model |
| Millennium Designed by Dick Glismann |
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| This gem design was made available for the first time at the Award Luncheon of the Intermountain Faceters Guild on March 11, 2000 in Ogden, UT. The Millennium cut was developed by Dick Glismann. It uses the pavilion of the Lace Cut with a diamond facet crown added in place of the simpler lace design crown. In light-colored material, it yields a very bright and attractive gem. Please give it a try! You will be pleased with the results. | |
| Angles for R.I. = 1.54 | 97 facets + 16 facets on girdle = 113 |
| 16-fold, mirror-image symmetry | 96 index |
| L/W = 1.000 T/W = 0.619 T/L = 0.619 P/W = 0.444 C/W = 0.150 | H/W = (P+C)/W+0.02 = 0.614 P/H = 0.722 C/H = 0.245 |
| Vol./W^3 = 0.215 | Brightness at 0° tilt RI = 1.54: COS = 65.3 ISO = 69.0 RI = 2.16: COS = 69.5 ISO = 86.1 |
| Pavilion | |||
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| 1 | 42.00 | 03-09-15-21-27-33-39-45-51-57-63-69-75-81-87-93 | |
| g2 | 90.00 | 03-09-15-21-27-33-39-45-51-57-63-69-75-81-87-93 | |
| 3 | 41.58 | 96-06-12-18-24-30-36-42-48-54-60-66-72-78-84-90 | |
| Note: Use 1200 lap for #3 facets. Best to rub by hand with stationary lap. Leave #3 facets unpolished. | |||
| Crown | |||
| a | 47.00 | 03-09-15-21-27-33-39-45-51-57-63-69-75-81-87-93 | |
| b | 40.00 | 96-06-12-18-24-30-36-42-48-54-60-66-72-78-84-90 | |
| c | 35.00 | 03-09-15-21-27-33-39-45-51-57-63-69-75-81-87-93 | |
| d | 30.00 | 03-09-15-21-27-33-39-45-51-57-63-69-75-81-87-93 | |
| t | 0.00 | Table | |
MILESTONE
| GemCad Ray Traces for RI = 1.54 | ||
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| Random Model | Cosine Model | ISO Model |
| GemCad Ray Traces for RI = 2.16 | ||
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| Random Model | Cosine Model | ISO Model |
| Milestone Designed by the Dare Devil Faceters |
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| The original citrine Milestone cut by the Dare Devil Faceters weighs 5280 carats | |
| Angles for R.I. = 1.54 | 313 facets + 24 facets on girdle = 337 |
| 24-fold, mirror-image symmetry | 96 index |
| L/W = 1.000 T/W = 0.563 T/L = 0.563 P/W = 0.579 C/W = 0.180 | H/W = (P+C)/W+0.02 = 0.779 P/H = 0.743 C/H = 0.231 |
| Vol./W^3 = 0.298 | Brightness at 0° tilt RI = 1.54: COS = 41.0 ISO = 45.1 RI = 2.16: COS = 55.6 ISO = 71.8 |
| Pavilion | |||
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| g | 90.00 | 96-04-08-12-16-20-24-28-32-36-40-44-48-52-56-60-64-68-72-76-80-84-88-92 | |
| h | 70.00 | 96-04-08-12-16-20-24-28-32-36-40-44-48-52-56-60-64-68-72-76-80-84-88-92 | |
| i | 64.00 | 02-06-10-14-18-22-26-30-34-38-42-46-50-54-58-62-66-70-74-78-82-86-90-94 | |
| j | 58.00 | 96-04-08-12-16-20-24-28-32-36-40-44-48-52-56-60-64-68-72-76-80-84-88-92 | |
| k | 52.00 | 02-06-10-14-18-22-26-30-34-38-42-46-50-54-58-62-66-70-74-78-82-86-90-94 | |
| l | 49.00 | 96-04-08-12-16-20-24-28-32-36-40-44-48-52-56-60-64-68-72-76-80-84-88-92 | |
| m | 46.00 | 02-06-10-14-18-22-26-30-34-38-42-46-50-54-58-62-66-70-74-78-82-86-90-94 | |
| n | 43.00 | 96-04-08-12-16-20-24-28-32-36-40-44-48-52-56-60-64-68-72-76-80-84-88-92 | |
| Crown | |||
| a | 52.00 | 96-04-08-12-16-20-24-28-32-36-40-44-48-52-56-60-64-68-72-76-80-84-88-92 | |
| b | 46.00 | 02-06-10-14-18-22-26-30-34-38-42-46-50-54-58-62-66-70-74-78-82-86-90-94 | |
| c | 40.00 | 96-04-08-12-16-20-24-28-32-36-40-44-48-52-56-60-64-68-72-76-80-84-88-92 | |
| d | 36.00 | 02-06-10-14-18-22-26-30-34-38-42-46-50-54-58-62-66-70-74-78-82-86-90-94 | |
| e | 33.00 | 96-04-08-12-16-20-24-28-32-36-40-44-48-52-56-60-64-68-72-76-80-84-88-92 | |
| f | 30.00 | 02-06-10-14-18-22-26-30-34-38-42-46-50-54-58-62-66-70-74-78-82-86-90-94 | |
| g | 0.00 | Table | |
GREAT MOGUL
| GemCad Ray Traces for RI = 1.54 | ||
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| Random Model | Cosine Model | ISO Model |
| GemCad Ray Traces for RI = 2.16 | ||
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| Random Model | Cosine Model | ISO Model |
| The Great Mogul PC01023.GEM Tom Barbour |
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| Angles for R.I. = 1.54 | 181 facets + 20 facets on girdle = 201 |
| 20-fold, mirror-image symmetry | 80 index |
| L/W = 1.000 P/W = 0.000 C/W = 0.831 | H/W = (P+C)/W+0.02 = 0.851 P/H = 0.000 C/H = 0.977 |
| Vol./W^3 = 0.359 | Brightness at 0° tilt RI = 1.54: COS = 15.2 ISO = 20.8 RI = 2.16: COS = 62.0 ISO = 77.3 |
| Crown | |||
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| 1 | 90.00 | 80-04-08-12-16-20-24-28-32-36-40-44-48-52-56-60-64-68-72-76 | |
| 2 | 84.00 | 80-04-08-12-16-20-24-28-32-36-40-44-48-52-56-60-64-68-72-76 | |
| 3 | 80.00 | 02-06-10-14-18-22-26-30-34-38-42-46-50-54-58-62-66-70-74-78 | |
| 4 | 69.50 | 02-06-10-14-18-22-26-30-34-38-42-46-50-54-58-62-66-70-74-78 | |
| 5 | 67.00 | 80-04-08-12-16-20-24-28-32-36-40-44-48-52-56-60-64-68-72-76 | |
| 6 | 59.50 | 80-04-08-12-16-20-24-28-32-36-40-44-48-52-56-60-64-68-72-76 | |
| 7 | 57.00 | 02-06-10-14-18-22-26-30-34-38-42-46-50-54-58-62-66-70-74-78 | |
| 8 | 51.50 | 02-06-10-14-18-22-26-30-34-38-42-46-50-54-58-62-66-70-74-78 | |
| 9 | 49.00 | 80-04-08-12-16-20-24-28-32-36-40-44-48-52-56-60-64-68-72-76 | |
| 10 | 43.00 | 80-04-08-12-16-20-24-28-32-36-40-44-48-52-56-60-64-68-72-76 | |
| t | 0.00 | Table | |
JULIANA
| GemCad Ray Traces for RI = 1.54 | ||
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| Random Model | Cosine Model | ISO Model |
| GemCad Ray Traces for RI = 2.16 | ||
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| Random Model | Cosine Model | ISO Model |
| Juliana PC21010.GEM Donald W. Hartley |
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| Angles for R.I. = 1.54 | 73 facets + 8 facets on girdle = 81 |
| 8-fold, mirror-image symmetry | 96 index |
| L/W = 1.000 T/W = 0.556 T/L = 0.556 P/W = 0.434 C/W = 0.156 | H/W = (P+C)/W+0.02 = 0.610 P/H = 0.711 C/H = 0.256 |
| Vol./W^3 = 0.194 | Brightness at 0° tilt RI = 1.54: COS = 75.4 ISO = 82.7 RI = 2.16: COS = 73.8 ISO = 91.0 |
| Pavilion | |||
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| g1 | 90.00 | 06-18-30-42-54-66-78-90 | |
| 2 | 47.50 | 06-18-30-42-54-66-78-90 | |
| 3 | 41.50 | 03-09-15-21-27-33-39-45-51-57-63-69-75-81-87-93 | |
| 4 | 42.00 | 06-18-30-42-54-66-78-90 | |
| Crown | |||
| a | 45.00 | 06-18-30-42-54-66-78-90 | |
| b | 35.50 | 03-09-15-21-27-33-39-45-51-57-63-69-75-81-87-93 | |
| c | 35.00 | 06-18-30-42-54-66-78-90 | |
| d | 30.00 | 06-18-30-42-54-66-78-90 | |
| t | 0.00 | Table | |
Here are a few pictures of some of these CZ gems from my collection.
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CLOSING REMARKS
In preparing these remarks, an author is presented with a problem with no easy solution that I know of. Namely, much of what needs saying and the suggestions to be presented have been covered in many ways before. How can one present a rather complete presentation that can be helpful to both new faceters and some of the more experienced faceters? To repeat everything each time can become boring to many; yet, left-out information may be just what a new faceter needs.
In this pamphlet, I have tried to find a middle ground–something for everyone. Now, I would like to make First-Year Faceters a deal. In 1996 I presented a talk at this symposium entitled “100 & 1 FACETING TIPS FOR FIRST YEAR FACETERS (AND OTHERS)” If you are a First-Year Faceter or a beginner of any skill level and would like a copy of the pamphlet given out at that meeting, send me a note with your name and Snail Mail address and I’ll mail you a copy. It may be a bit slow getting to you, as I travel a lot, but I will send them as my time permits. The price in right–they are free.
Carl M. Unruh
21 Shorecrest Place
Port Townsend, WA 98368