Gram Wagon Wheel Design


The answer is a qualified yes. But like everything else in life there are some trade offs Below is a design called “Gram Wagon Wheel”. This is basically a redo of an old design, it has been around a long time under different names, this is just my version of it.

Gram Wagon Wheel

Notice that the pavilion is just a straight bottom, single tier, so is the crown for that matter. I chose this design because of it’s simplicity, it is easy to make in Gemcad, and simple to cut. The single tier on the pavilion (and crown) offer the best optical performance for comparing tilt brightness, at least that I have found so far.

Gram Wagon Wheel 41 degree pavilion, 13 degree crown tilted 10 degrees

Above is is face up (zero tilt) 41 degree pavilion / 13 degree crown. As you can see there is good brightness and very little hole at the crown apex, it is really just about covered by the center point of the crown. Below is the same design tilted 10 degrees (on the “x” axis only), now you can see the small hole at the apex, and some tilt drop out around the edges. The design actually has a decent tilt brightness. Much better than the standard round brilliant I used in the first article in Quartz and other low refractive index materials. However I would not really call this good tilt brightness, and this is only tilted to 10 degrees, it will get worse with more tilt.

41 degree pavilion, 16 degree crown41 degree pavilion, 16 degree crown tilted 10 degrees

Above is 41 degree pavilion / 16 degree crown. As you can see the higher crown actually gives more reflection out around the girdle, and a more interesting reflection on the face up view. The hole at the apex is maybe a little larger, but not much. On the 10 degree tilt view the hole at the apex is slightly larger and the 1/2 moon fall out at the girdle is a little smaller. Basically a trade off…

42 degree pavilion, 13 degree crown42 degree pavilion, 13 degree crown tilted 10 degrees

Above is 42 degrees pavilion / 13 degree crown. The reflection is better out around the girdle, and the same in the center. Tilted the apex hole is similar, and the moon around the girdle is about the same. But notice at 12 o’clock two of the pavilion facets are starting to shadow and drop out, because of the tilt. You could just see it starting in the last design above, if you look closely.

42 degree pavilion, 16 degree crown42 degree pavilion, 16 degree crown tilted 10 degrees

Above is 42 degrees pavilion / 16 degree crown. The overall brightness, especially in the random light model is getting flatter/darker, but notice the band out around the girdle is gone. The apex hole in the center about the same. The tilt on this one is interesting, the moon out along the girdle, is a bit smaller, the apex hole is the same and the 12 o’clock facets that were in shadow, are not now. You can really begin to see the trade offs happening.

43 degree pavilion, 13 degree crown43 degree pavilion, 13 degree crown tilted 10 degrees

Above is 43 degree pavilion / 13 degrees crown. The face up is about the same as the last one, maybe a little less pattern. The tilt is about the same with the exception that there are two facets at 6 o’clock dropping out now, remember this is the same tilt on the “x” axis. It is funny that the two facets falling out have reversed.

43 degree pavilion, 16 degree crown43 degree pavilion, 16 degree crown tilted 10 degrees

Above is 43 degree pavilion / 16 degree crown. Notice that the Random light ray trace (left, in the set of three) is actually brighter and more interesting. The apex is about the same. On the tilt there are 4 facets dropping out at the bottom of the design and the moon shape at the top girdle is smaller.

What does this all add up to? Just like in physics class, there is an opposite and equal reaction for every action the designer takes while creating a new design. The trick is in having experience and maybe some luck in getting the proper balances. Some of this boils down to personal taste really. What do you like? Below, I think the best comprise of all these variations is 41 pavilion / 16 crown (I have tried higher crown angles, but the apex hole gets to large for me). I think that this one is the most interesting and has the best life and patterns (see the spokes of the wheel, you will in the cut stone). Patterns are a major part of what I personally look for in a design. But other people might like one of the others.

41 degree pavilion, 16 degree crown41 degree pavilion, 16 degree crown tilted 10 degrees

Wondering what a table would do? Below is the same design with a 41 degree pavilion / 16 degree crown and a small table, to cover the apex hole. As you can see the table takes care of the hole in the face up brightness, but when it’s tiled the same 10 degrees on the “x” axis, the drop out is there just like in the round brilliant in my other article. As you can see the apex crown does solve some of the drop out, but there is a price, both in appearance of the design and angles. Notice where the table is in the face up view, it is brighter, this will increase as the table is made bigger, unfortunately the drop out when the design is tilted will get larger as the table does.

41 degree pavilion, 16 degree crown

Below is the same design (no table) 41 degree pavilion / 16 crown in refractive index 1.76 (Sapphire). Notice that the apex hole is still there although a bit smaller, the higher refractive index of Sapphire does not get rid of it, but does help minimize it. The higher R.I. does not seem to make a lot of other differences, although I think the crown could be raised a bit without much loss.

R.I 1.76 - 41 degree pavilion, 16 degree crownR.I. 1.76 - 41 degree pavilion, 16 degree crown 10 degrees tilt

Below is the standard round brilliant (41 pavilion / 42 crown) with a table in sapphire for easy comparison from my other article. There is no question which one I would rather cut for brilliance. No hole in the center in the higher refractive index of Sapphire, interesting isn’t it?

41 degee pavilion 42 degree crown 1.76 R.I.41 degee pavilion 42 degree crown 1.76 R.I. tilted

Like I have said before, I do look at tilt brightness when I am designing. But as you can see there is often not going to be much you can do to improve it, especially in low refractive index designs. Interestingly enough I have come up with some checker board designs that get the best of both worlds, both tilt and face up brightness. But in most designs you are going to make some compromises, depending on what you are designing for.

This article is a follow up to my What is Face up Brightness and Tilt Brightness? Please read this article first, I will make some references to it, along the way in this one.

Gram Faceting Archive of Information
This edited version of an article by the late Jeff Graham is part of a special archived informational series from Gram Faceting. Used with permission.