I would like to comment on Mr. Galarneau’s recent tourmaline post.
First, I went to Mr. Girardeau’s website and inspected some of his
cutting, most impressive indeed!
Having been involved in cutting a couple of hundred thousand
Namibian tourmalines over the last 10 years I feel qualified to make
some comments on tourmaline in general and specifically about the
material from various mines in Namibia’s Erongo region where I live.
Over the years we noticed a tendency of Namibian material to grain
pick when preformed too aggressively. Ultimately by using worn 600
grit wheel to preform, most of the surface picking was eliminated.
By using this technique we also were able to grind out many of the
ubiquitous surface micro stress cracks that are perpendicular to the
c axis. The fact is most pleasantly colored gem tourmaline seems to
be stressed regardless of its origin.
Given that Mr. Galarneau is doing concave cutting I’m wondering if
by definition this cutting style requires aggressive abrasive use? If
so then that may be part of the problem.
Mr. Galarneau also suggests that the problems in the pink tourmaline
are directly attributable to heat-treating. I would respectfully
point out that pink tourmaline is frequently subjected to multiple
treatments, including exposure to hard radiation. The process
involves first heating sufficiently to remove all color, then
exposing it to a reactor to turn it lipstick pink. I would agree that
heat may contribute to a stones failure, but I would suggest that
radiation induced lattice structure damage might be a larger
contributor to the failure rate of pink tourmaline.
With regards to the failure in the bright green Namibian material
the only bright green material that has been produced in the last few
years was a notoriously stressed pocket from the Usakos mine. One
minor point, Namibian green tourmaline rarely improves with heating,
the notable exception to the rule is the best greens from Neu
Schwaben, consequently most dealers buy it as a WYSIWYG product
knowing that a stay in their Neycraft won’t improve it. This is
largely a function of the molecular iron content and its valence.
With the Namibian green tourmaline and green tourmaline in general
it is the degree of “greenness” that controls its response it heat,
if it is a pure green with yellow overtones and a black or very dark
c axis it won’t burn. If it’s got a bit of blue and the c axis will
at least pass some light then it will generally improve slightly,
normally becoming brighter rather then changing hue. If it has an
open c axis then it will definitely improve both in terms of
brightness and color.
If anyone is interested in seeing an excellent selection of Namibian
tourmaline including a very deep inventory in calibrated stones
please visit me at this year Tucson show, room 153 in the Pueblo Inn.
Kind regards,
Chris
Johnston-Namibia C.C.
Chris Johnston
PO Box 354 ~ Omaruru ~ Namibia
T/264-64-57-0303 F-264-64-57-0548