I’ve written some articles on tilt brightness, the brightness a stone shows when rocked, in one or more directions. You can review these articles on cutting for tilt brightness and using an apex crown to improve tilt brightness. I’ve emphasized how adding tilt brightness to gem designs involves making trade-offs. However, novice faceters, in particular, still ask, “Should I add tilt brightness if I can?”
Do You Need High Tilt Brightness and High Ray Trace Numbers for Good Gem Designs?
The simple answer to these questions? No, not really.
Should gem cutters look for these elements when choosing a design? Maybe. It depends on what you like and want from a design.
Let me explain. The first thing novice faceters need to know about gemstone designs is that they’re all compromises. None are perfect. You’ll have to give a little in one area to get a little in another. What does that mean? In our case, let’s look at tilt brightness. To get better tilt brightness, a designer may have used a different angle than the optimal one for a higher light return (or brilliance). Thus, in that design, less face-up brightness means more tilt brightness.
Remember, to achieve their overall gem design goals, designers will make compromises between various elements, such as refractive index (RI), cut, shape, size, color, face-up and tilt brightness, and so forth.
So, say you’re using the handy BOG program. This “Better Optimizer for GemRay” shows how gem designs will perform, given certain conditions, including tilt. Will using a computer program like this one affect how you consider tilt brightness?
First, let’s make a few clarifications.
Low Refractive Index Gems
There’s not a lot you can do to get a high degree of tilt brightness from low RI gems. In almost all gem designs, these stones just don’t work all that well when tilted. Sure, you can make some improvement, but it’s usually small. Furthermore, you’ll have to make other changes, which often impact the overall design objectives. Again, as with many things in life, you must make compromises.
Most natural gemstones available as rough for hobbyists and even professional faceters fall into the lower RI range, below 1.67. This covers such popular gemstones as:
- Quartz (1.54) – amethyst, citrine, rock crystal, smoky.
- Feldspar (1.518-1.526) – moonstone, sunstone.
- Beryl (1.562-1.602) – aquamarine, emerald, morganite, goshenite.
- Tourmaline (1.603-1.655) – all types.
- Topaz (1.609-1.643) – all types.
Of course, exceptions exist in the marketplace. You might acquire a zircon (1.79-2.011) or occasionally a nice sapphire (1.757-1.779). Except for garnets, there is generally not a lot of commercial rough available with higher RIs. I haven’t covered every type of gem material available, but you get the idea.
Basically, if you’re cutting a gem design intended for natural gemstones, the designer most likely factored lower RI rough into the overall goal for the finished gem.
Different Gem Rough May Have Different Design Priorities
Many factors may impact gem design choices for natural rough. For example, gem yield will likely play a major factor in a design for an expensive piece of rough. (Greater than tilt and probably face-up brightness, too). For other types of material, the rough shape, color orientation, dichroism, etc., may affect design choices and performance.
Real World Factors
Don’t forget to consider the obvious. Namely, what does the design look like? To get the most out of a piece of rough, and then set and sell it, you’ll need to consider many basic factors before high tilt brightness. A program can’t tell you what will sell well or even what “looks good.” You still must evaluate the virtual possibilities according to your real world needs. Speaking of the real world, when you actually cut a gem you might encounter unforeseen circumstances. Breaks and discoveries of unknown flaws will occur and affect your design choices. Experience and, sometimes, just luck will come into play.
How is a Violin Competition Like a Gem Design?
An experience I had years ago comes to mind. I had a girlfriend who played the violin. She once learned of a violin competition at a local college, so we went. (I had my doubts but hoped the music would be worth listening to).
Well, let’s just say the music (loosely speaking) sounded like fingernails across a chalkboard. I expected the musicians to jump up and smash their instruments against the stage like rock stars. Alas, I wasn’t so lucky. The violinists were some of the best around, or so I was told.
Later, my girlfriend told me that experts could recognize and appreciate what the musicians performed. I’m not sure I believed that. However, I’d wager not a single non-musician would even call it music. Furthermore, they would probably run away from it if they could, no matter how technically sound it was. (I wish I could’ve run away).
So, how does this relate to faceting and gem designs?
A few degrees (or even a fair amount) of tilt brightness one way or another may interest us faceters. However, only an expert could see a slight improvement. Even if the improvement were 15 or 20° with a high RI gem, non-faceters won’t know the difference. Most finished gem buyers couldn’t care less, even about face-up brightness (at least as far as a number on a ray trace is concerned). People choosing gem designs for their rough also won’t care much.
And I’m not sure they should.
What Makes a Good Gem Design?
What’s important to both a faceter cutting a gemstone and a customer buying one? The appearance of the finished gem. By this, I mean color, brightness to some extent, the reflected play of the facets, and the design’s shape and uniqueness.
If you’re choosing a gem design, ask yourself the following:
- Is the design attractive as well as a good optical performer?
- Does it suit the rough you will cut?
- Can you sell the combination of rough and design?
Most modern gem designs will meet these goals and cut nice stones. Few people can see a few degrees of tilt difference in a design. By the time you set the gem, I seriously doubt anybody could tell the difference. Remember, a jewelry setting can change a gem’s appearance substantially.
If you’re selling finished gemstones, price and ease of setting also constitute important factors when choosing a gem design. However, in my opinion, the most most important question to ask is: Is the gemstone pretty? Does it have that WOW or POP we all look for?
Consider the Overall Gem Design Goals Before Making Changes
If you can gain tilt brightness and stay true to the gem design goals, then, by all means, factor in tilt brightness. If you need to change the design significantly to gain a few degrees of tilt brightness, I don’t think it’s worthwhile. You’re sacrificing the finished gem’s appearance for a small change, at best, especially for low RI gems.
Most modern gem designs do well at striking a balance between the factors that affect a gem’s appearance and performance. So, choose a design that you think will work best for your rough and that you’ll enjoy cutting.