Lapidary Techniques: Cutting & Faceting Tourmaline
by Bruce A. Fry
Considering Color & Weight Retention
When cutting rough tourmaline, as with any colored gemstone variety, the lapidary must consider both color and weight retention. The unique complexity of cutting tourmaline comes into play not only with the great variety of colors, but with the distribution of color.
Not all tourmalines have two or more colors, but when they do, the choice of cut can either blend or isolate the different colors. Tourmaline is the jester of gemstones - because it is so endlessly entertaining! The color down the c-axis (down the barrel of the pencil) is either the same color, a richer shade of the same color, or a completely different shade of the color than the a/b color. Note: the a and b-axis, which are 90 degrees to the c-axis, must always be identical because of the geometry of the crystal. You can cut the stone to blend the c axis color and the a/b-axis colors completely, but you can never eliminate the c-axis color in the face-up view of a practical gemstone.
Color Mixing in Cut Tourmaline
The shape of the tourmaline crystals also places limits on the mixing of color. This is particularly so when the tourmaline is in long, slender crystals with an optically dense c-axis (closed ends). For these crystals, the only practical cut has steep ends and a rectangular shape. Bi-colored tourmaline and stones with colors that don't mix well together also tend to have rectangular shapes with steep ends which minimize the mixing of the colors.
Other tourmaline color mixes such as "sea-foam tourmaline" from Afghanistan have yellowish green c-axis along with a bluer a/b-axis, which beg to be mixed into a swirling sea of color. I have also found that cutting a tourmaline with its table at 45 degrees to c-axis can produce a beautiful stone and retain weight.
The blue-spruce green specimen of dichroic elbaite (below, left) was cut so that the lighter a/b-axis forms a vertical line through the middle of the stone. The rest of the facets blend the richer c-axis into the a/b-axis to bring out the color. This faceting pattern is a Barion cushion-cut which was designed by Bill Graham.
Dichroic elbaite form Mozambique
Dravite tourmaline form Mozambique
The faceted orange-brown dravite in the photo above (right) is cut so that the c-axis, which is always as saturated, or more saturated than the a/b-axis, comes out of the stone perpendicular to the table. This way there is only one color face-up, but you will see more of the a/b-axis mixed with the c-axis as you tilt the stone. Cutting a tourmaline in this way gives you the richest color that the rough is capable of generating.
Tourmaline generally cuts and polishes easily, but its complex nature can show itself in stress-induced chipping, breaking and scratching while cutting and polishing. The facets perpendicular to the c-axis can cut very differently to the facets parallel to the c-axis. The speed of the polish, flatness of the facets, and scratching can all be affected.
Many cutters use one or more rounds of diamond of varying grades, while others used oxide polish such as alumina to polish tourmaline in one step. Either technique can produce an excellent polish, but some commercially cut tourmaline tends to have a mediocre polish. This is because of the time necessary to truly get tourmaline to polish well, and commercial cutters generally do not spend the necessary time due to financial considerations. A well polish tourmaline with the correct faceting angles on its pavilion and fine color can withstand a critical comparison with the beauty of any gemstone variety.
Cutting Indicolite Blue Tourmaline
Indicolite is typically cut in longer-ratio emerald cuts because of its crystal shape, and its overly saturated c-axis, but some indicolite has only one shade and intensity of blue, and these specimens are appropriately cut to retain weight, and produce the most beautiful gemstone possible.