BY JERRY L. CAPPS

In Step-by-Step of Lapidary Journal January 2001, page 52, Jerry L. Capps explains how he used GemCad to improve one of his own designs, and then gives complete cutting instructions for his improved “Markova Interlochen.”

If your experience with gemstones is limited to admiring and wearing them, setting them, grinding cabochons, or only thinking about trying to facet, you might expect that only a very accomplished facetor would ever try to design a new cut. It’s a funny situation, though.

It’s true that most beginning facetors do not design their own cuts right at the start — at least not on purpose. But beginning facetors, like beginners of all kinds, tend to make mistakes. Maybe they set their faceting machine index wrong for the design they were trying to cut, essentially reorienting the design, and Wow! — a new design with their very first stone.

By accident or on purpose, once you get started on designing cuts, you’ll want to continue with some basics in mind. Simple designs, such as a round, are usually easy to compose directly on the faceting machine. It’s a matter of deciding how many facets will constitute the outline shape, or the girdle. Depending upon which index gear you installed on your machine, you’ll need to divide the gear by the number of facets desired, and use the appropriate resulting indexing — very basic stuff, and nothing too mathematical. But there are other considerations, too, especially those that pertain to your choice of material. For instance:

• Refractive index (R.I., a measure of the degree to which light is bent when it passes between media of different densities, such as going from air to a transparent gem material). The R.I. determines the critical angle needed for pavilion facets to reflect light back out to the viewer. It’s the job of the crown facets first to gather light into the stone, and then to chop the light up into pieces before it exits again, helping to give the stone “life.” In designing a gem, you need to pay special attention to the critical angle of your material and not exceed it on the pavilion.
• Cleavage: how readily does this material cleave, in how many directions, and which ones?
• Heat sensitivity: do you need to dop with wax, epoxy, or super glue?
• Singly or doubly refractive? If doubly, this increases the chances of better dispersion with a higher crown, as opposed to the best brightness of a lower crown.
• Proportion of crown height to pavilion depth: should you use the proportions set up many years ago for diamond? Ideal diamond proportions were determined for the dispersion capability of diamond and not necessarily maximum brightness, as well as for the looks of the stone when set protruding above the mount.

However, these proportions do not always apply to colored stones.
• c-axis (the “long” direction of a crystal): a dark c-axis dictates a rectangular design to maximize passage of light from limited directions.
• Hardness: do you have the appropriate polishing lap? Choices include ceramic, zinc, copper, tin, Corian, Plexiglas . . . and on and on.
• How light or dark the material is: do you cut it deep or shallow to maximize brightness or color?

All of these factors and more are important, and fortunately, a lot of the information you need is easy to find. Many facetors rely on Faceting for Amateurs, a hardcover book written and published by Glenn and Martha Vargas [the Vargases were recently inducted into the National Lapidary and Rockhound Hall of Fame for their contributions; see “2001 Hall of Fame,” November 2001]. For many years, Glenn and Martha were teachers of a faceting course at the University of Texas. Besides the all-important refractive index, other properties of various gem materials are given, alphabetized, in their book, including heat sensitivity, suggested laps for polishing, hardness, color variety in each material, main locations where these materials are apt to be found, and so on. This book is considered the bible for beginning facetors and a valuable resource for advanced cutters.

WHERE TO GET GEMCAD?

GemCad homepage www.gemcad.com

Larry Davis ldavis3@kscable.com

John and Barbara Franke jfranke@gemcutter.com

VIRTUAL VIRTUES.
If you are designing as you cut an actual stone, keeping track of your trials and errors with pencil and paper can be tedious at best. Instead of drawing a diagram by hand, perhaps with the aid of a calculator, you might try using GemCad, a computer program developed by Robert W. Strickland specifically for designing gem cuts, along with GemCad’s support programs GemPrint, GemRay, and GemFlick for analyzing, printing, and viewing GemCad designs. GemCad computes all the mathematics automatically, and you don’t have to write down or remember a thing: GemCad keeps track of it all for you.

If you’ve tried designing while faceting, you’ll recall the difficulty you had remembering the index you chose, the angle, and precisely how deep you finally decided to cut.

By the time you finished, the stone was probably much smaller than you expected or than it need have been. Using GemCad allows you to come up with the same initial design without the necessity of your memory or using up any materials. It further allows mistakes to be “undone,” which saves a lot of material from going down the drain.

Besides making designing so much easier, GemCad can also “tangent ratio” a series of facets to maintain the same look at a higher or lower set of angles. For example, upon completing the pavilion, have you ever run out of enough material to cut the crown? Unfortunately, you can’t just reduce all the angles by two or three degrees. It would destroy the look or configuration and proportion of the crown design. GemCad’s tangent-ratio function can revise the entire crown — all angles, lower or higher — and by doing so will maintain the look and proportions of the design. You could also do this with a calculator, but it requires more math than I choose to undertake. GemCad works it all out perfectly with a single keystroke and in just a few seconds.

Another feature of GemCad is its ability to change the indices from vertical to horizontal — by 90 degrees. If an oval is designed and drawn vertically, and your V-dopstick transfers in the opposite direction, you have a really big problem. Assuming you’re using a 96 gear, with GemCad, you simply assign the 96 to the right or left side instead of the top or bottom. This alters all indices so that while the drawing may be vertical, the indexing is horizontal. An alternative method is to use the “r” command and rotate the drawing, which leaves the index gear as originally specified, but turns the drawing by whatever amount you wish. Neat stuff, huh?

GemCad’s advantages should start being obvious by now, but there’s more. Besides automatically keeping track, calculating complex mathematics, and allowing you to correct mistakes without having to waste possibly valuable material, GemCad also saves you time, letting you figure out a version of a cut in a matter of minutes instead of what could be days.

How long does it take to facet a real stone? An experienced facetor using wax for dopping and transferring could finish a Standard Round Brilliant (SRB) in two hours. At the other end of the faceting spectrum are the Australian International competition facetors, who may require three months to finish one out of three competition stones. (Fortunately, competition facetors are not professional facetors — they’d starve, even if they did have a perfectly cut stone.) With GemCad, a facetor can cut a virtual gemstone in two minutes.

If I’ve managed to convince you that GemCad is the way to go for facet designing and you want to try it, read on. What follows are directions for obtaining the program, installing it on your PC, and very fundamental instructions for using the program to complete a simple diagram with your first GemCad design.

DOS DILEMMA.
Many facetors who also use computers have avoided getting involved with GemCad primarily because they don’t want to have to bother with any DOS commands, which are executed by typing on the keyboard. Since the introduction in the early 1990s of Windows, which relies on icons, menus, and the use of a mouse, few new pc users have been familiar with DOS, and even those who remember the DOS days before Windows tend to think back on DOS with dread. This is unfortunate, since GemCad requires very few DOS commands: the program can be controlled almost 99.5 percent with a mouse.

Notice, though, that I said “controlled” — not installed. DOS commands may be required to install, and initially to open the program, and sometimes to configure the program for compatibility with an assortment of printers. After this, everything can be controlled with the familiar mouse and by simply answering the dialogue box.

The GemCad author has ingeniously given the user a choice of operating methods, via a mouse or letter commands; even better, these can be used interchangeably. Although GemCad has an assortment of menus from which a mouse can control every operation, the menu-driven system seems slow to anyone who has a fundamental knowledge of the keyboard and can memorize 10 to 15 letter commands (of over 50), which speeds things up considerably. The letter commands were devised in a common-sense manner and are easy for a facetor to remember because they relate to using a faceting machine.

GETTING STARTED

Start with the GemCad manual at www.gemcad.com/gemcad.htm

Read up on the GemCad Frequently Asked Questions at www.gemcutter.com/download/gemcad.txt

• Faceting Patterns, from Rockhounds.com • Search Orchid for Gemcad Discussions

GETTING GEMCAD.
There are numerous sources for obtaining the latest version 4.51 of GemCad. These sources most often allow you to download a Zip file, which will require unzipping before the program can be used.

Larry Davis is one source. His e-mail address is ldavis3@kscable.com. Another source is John and Barbara Franke, whose e-mail address for downloading GemCad is jfranke@gemcutter.com. Both John and Larry are very personable, and most willing to help. Having met John recently at the Portland, Oregon, gem show, I must say he is the most gentlemanly person I’ve ever encountered, and that includes a lot of really great people.

There are other opinions on how to install the GemCad program, but this is my recommendation. It’s a really good idea to start by creating a folder for the program. In DOS terms, this is a directory. Note: I include quotation marks around the commands you need to type in, but you don’t type in the quotation marks themselves, only what’s inside them. The same is true for describing what appears on the screen: it’s in quotes here but not on the screen.

With the mouse, go to Programs and access the MS-DOS. You will see “c:\windows”; type “cd..” (that is, cd followed by two dots or periods, no spaces) to get to the root “c:\”; then give the DOS command “md gemcad” (make directory of GemCad). Now give the DOS command “cd gemcad” (change directory to GemCad).

From this directory, you can also create a subdirectory for GemFrame by giving the DOS command “md gemframe” (make directory for GemFrame). Again, give the DOS command “cd gemframe” to put your cursor into the subdirectory. You should see “c:\gemcad\gemframe” on your screen. These directories are required to keep your designs from getting mixed up with the designs for analysis, which you may want to delete after finishing the analysis. To go back one or more directories, simply give the command “cd..” as many times as you want to go back directories.

When you download GemCad, or GemPrint, be sure to specify placing it in the c:\gemcad directory (folder). If you have the option of downloading some of the other support programs, be sure to put GemRay and GemFlick in the c:\gemcad\gemframe directory. I believe there is a fee for GemFlick, but let me assure you, it is a bargain.

After downloading GemCad, you’ll want to start it up. From the “c:\gemcad” prompt, you must give the DOS execute command “gemcad” (type it in and hit Enter). Your monitor will show: “do you want to configure the program and if so type ‘c’”— at this moment, you don’t want to, since configuring the program is primarily for printing instructions or setting the screen proportions. You can come back to this at the next session and play with it if you wish. Use the Enter key or Space bar and the GemCad diagramming blue screen will be displayed.

Now, just as in setting up your faceting machine, you must set some parameters — like which gear tooth to install, the number of facets you want around the gemstone (symmetry), and which material you wish to design for (by setting the R.I.). All letter commands are case sensitive, so when it calls for a capital letter, be sure to use a capital letter.

To set the parameters desribed above, start with the command “g” and answer “96” to the query at the top of the screen. The second question will be what number you wish at the bottom. It’s advantageous to have the diagram correspond with most machines, so place the 96 at the bottom. Now you must give the symmetry, so give the command “y” and specify “8” (you can specify what you want; I’m just walking you through with an example). Then specify mirrored or not; answer “y” and then give the command “I” which stands for Refractive Index. Specify “1.54” for quartz. The upper left corner of your screen will confirm the R.I. and display the critical angle for material with this R.I. Most of these parameters are set in the configuration file as defaults, and can be changed when opening GemCad or at any time while designing. Ok, now all parameters are set and we can go forward with designing.

FIGURE A

FIGURE B

FIGURE C

The next command requires using the mouse or the arrow keys. Position the cursor on the vertical line of the drawing, and move it to near the bottom of the drawing (stay on the line). When you get within 1/4 inch of the bottom (of the drawing vertical line), give the command “e” (for edgepoint), and answer the question “y”es. You may turn off the target cross line with the Space bar. Next, give the command “a”ngle, then specify “90”; give the command “i”ndex and specify “3”: you should now have the 16 pavilion break facets and the 16 girdle facets on all four sections of the screen.

Let’s assume you don’t want any pavilion main facets, and proceed to the transfer. To transfer (so you can do your drawing in the upper left section), type the command “x” and the transfer will be completed. From here, place the cursor in the upper right (labeled “SIDE”) just to the left (about 1/16 inch) of the present girdle line, at the bottom of the drawing (see Figure A - right).

Specify “e” for edgepoint, answer “y”es, then give the command “i”ndex, specify “3”; then give the command “a”ngle specifying “40” (see Figure B). This will give you the 16 crown break facets with a level girdle.

From here you can continue using the letter commands or the menu commands with the mouse in the upper left diagram. For the crown mains, position the cursor at the intersection of the two bottom crown break facets and specify “m” for meetpoint. Answer “y”es, then give the command “a” for angle, specifying “36”; then “i” for index, specifying “96” (see Figure C).

Now you’re initiated into GemCad. For more detailed lessons, I suggest contacting Larry Davis (see the section on downloading), who has a Web site devoted to teaching GemCad.

MEETPOINTS & BUILDING BLOCKS.
GemCad allows changing angles and indices, replacing and overcutting facets, and an assortment of other features. It is particularly useful in establishing meetpoints.

While novices tend to feel that meetpoint faceting (in which tiers of facets meet precisely) is more accurate than they need, it is for their benefit. Meetpoints make it easier to follow facet sequencing and attach tiers together. Without the depth dimensions that meetpoints provide, a design is not precise enough to be truly repeatable. That is, while you could cut an attractive stone based on a design, you’re likely to have a difficult time cutting another stone just like the first one, as you’d want to do to cut matched stones for a pair of earrings. Instead of looking on meetpoints as obstacles, try to appreciate the ease and simplicity of the system.

The best GemCad designs use building blocks, by starting with the facets closest to the girdle and working toward the culet or toward the table/apex. These building blocks attach each tier to the previous tier. It is a predictable and easily followed system when applied to your faceting machine, and is the essence of meetpoint faceting. Many published diagrams don’t use the building blocks, and I find them to be nearly impossible to cut except by guessing at how deep a particular tier is supposed to be, or how far this facet or tier should extend.

GemCad can override the building block sequence, but I recommend against overriding, as this is poor methodology and could lead to the kind of problem described above. The normal sequencing of GemCad nearly mandates a building block (meetpoint) style. However, if the “G”lossary command is used for inserting precise directions as each tier is made, there can be little misunderstanding about the depth of a tier, even though abbreviated instruction may be necessary due to the limited line space allotted.

GemCad is a great tool, but use it with discretion, not haphazardly by adding some facets just because you can. Once you’ve tried this program, you’ll be hooked, especially if you can also use the analysis program GemRay or Gemflick, and GemFrame in conjunction with it. Join me and many others fishing at the ‘ol GemCad pond (“leaverite” rock skipping allowed, but no skinny dipping unless accompanied by the GemFlick movie maker!).

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Jerry L. Capps has won the Midwest Facetors Guild’s David B. Miller Award, the American Society of Gemcutters’ Pinnacle Award, and numerous other medals for his original designs and craftsmanship. He is ASG certified and a Supreme Master, and was on the U.S. team for the Australian International 2000 competition. He has taught GemCad for several years at an annual seminar in Michigan, and currently serves as President of the U.S. Facetor’s Guild (USFG).