Joined: Wed Apr 26, 2006 12:44 am Posts: 2056 Location: San Francisco
Here's a really nice (pick of the parcel) indicolite (no copper I know of) that measures 26mm x 8.9 mm. I am considering how to cut it and would like some advice on what the best cut should be on this to maximize the color/beauty and still have some flash.. any and all suggestions appreciated..
I shot it in sunlight and inside to get a good color range the bottom probably has the most accurate color.. the dark side to the right is an illumination artifact.. it's as clear all the way through as the top one.. one side does shade deeper (left on bottom two).
_________________ Custom Gemstone Cutting and various other activities!
Joined: Sun Oct 29, 2006 11:43 pm Posts: 514 Location: North Carolina
Jleb,
Blue tourmaline are STRANGE. For whatever reason, they have quirks that other tourmalines don't have.
When you cut the stone, try to skin off any 'rind' which shows cracks, however small. Many many people have problems with these cracks, that appear to be just surface cracks, propagating through the stone, usually hours to a day or two after you cut the pavilion.
I, among other folks, will cut the pavilion and then set the stone aside for a few days. Often enough that you do this, the stone splits into two or more pieces.
The most knowledgeably folks give the advice of cutting off the rind (including the crown side) and letting the stone rest for a day or so. There seems to be some kind of stress in blue tourmalines that wants to split the stones.
Next, what color is the C axis (down the length) These stones are most often dark/black on the C axis and you want to cut to minimize this.
Take a look at this cutting design (available for free):
Joined: Sun Dec 30, 2007 12:01 am Posts: 556 Location: Vancouver, Canada
Hello Jleb,
This is a copy of a post I made some time ago on another forum. Hope it helps;
Well tourmaline is undoubtedly the most 'magic'
gemstone we have, science has been slowly explaining some of it's
properties;
M. Louis Lemery, in 1717 concluded that tourmaline was magnetic and that
the magnetism could be induced.
Franz Ulrich Theodor Aepinus, concluded in 1756 "that not only friction
but heat also should develop the electric energy, both positive and
negative, of the tourmaline"(sic).
Since 1921 when piezoelectric minerals were first explored, tourmaline,
which is strongly piezoelectric has been used in gauges to measure
transient blast pressures.
We know that when piezoelectric material is distorted an electric and/or
magnetic charge is produced and vice versa piezoelectric material distorts
when an electrical and/or magnetic charge is applied or induced.
With tourmaline we know that distortion is not the only means of producing
a magnetic and electrical charge, temperature change, friction and
abrasion also do this. The effect however differs in strength and polarity
and of course will cause the crystal to distort according to that strength
and polarity. How much crystal oscillation we have going on at the same
time as cutting or more importantly, polishing will be a significant
factor in the failure rate.
Another source of failure is the rind. I find this term a bit of a misnomer
as we tend to think of a rind as the outer skin of something that is
growing inside. A crystal grows by deposition so the 'rind' is the newest
part of the stone, the core being the oldest. Now we know that the
crystal is formed over long periods of time and we know that it requires
heat and pressure, we also know that the tourmaline crystal will deform in
response to that heat and pressure whereas the new deposition will not be
so stressed.
As the crystal grows there will be unstressed growth covering stressed
growth until the heat and pressure changes and another cycle of growth
occurs. Flawless gems will only occur if the temperatures allow the
crystal to anneal as it grows. This does not necessarily mean that the
last growth was annealed when the stone was mined so there is every
possibility that just below the unstressed newest layer lies a crystal
core that needs to relax.
THE TOURMALINE PROCEDURE
Removal of the outer layer is universally recommended.
Using hand held dops to do this has been strongly suggested.
That all grinding and polishing should be along the length of the crystal
not across it, using fine grit freshly charged laps is universally
recommended.
The crystal has one end designated the head and the other the tail. All
cutting and polishing will be in the same direction. This means you need a
reversable motor to accomplish this. Many say you don't need to do this
but adherents claim 100 percent success rate.
Using prewarmed laps and warm water for cutting and polishing is strongly
recommended.
Heavy flushing during cutting and polishing is also strongly recommended
Accomplishing the entire cutting process as quickly as possible is highly
recommended. Leaving a half completed stone for another day's session is
warned against.
Annealing.
I don't know the source but I believe Farouq assigned it to Marc
Liccini. The suggestion is that brittle tourmaline can be annealed in a
toaster oven. 450F is the temperature that will change the colour or
saturation so it would probably be wise to stay below that. I have never
tried annealing tourmaline but the suggestion is that an annealed stone
has fewer untoward cutting characteristics and doesn't require as much
special care and attention. No experience, no comment.
Joined: Wed Apr 26, 2006 12:44 am Posts: 2056 Location: San Francisco
Ah really good stuff... I have all the JG books, so i'll look them up and report back..
Thx for the info on the rind.. I can see micro cracks in it.. and this makes sense.. I also have a rather large knowlege base on piezoelectric materials, mostly pzt ceramics ( I invented the "shockround" piezo bullet).
I will follow gemdr's advice rigorously, it looks very good, and knowing what I do about stress/relaxation in the materials, as well as fracture propagation, you do want all those gone asap..
I'll report back after it's 'skinned' I'll look at the designs now..
So the question is, should i use a cut that has a velvety smooth look to it, such as is used with emerald.. or something flashy.. If the stone is light the flashy might wash it out.. There is no gray mask on the stone.. so it has a beautiful sky to sunset blue gradation.. The c axis is open and a deeper blue than that end piece..
Still thinking..
_________________ Custom Gemstone Cutting and various other activities!
Joined: Sun Dec 30, 2007 12:01 am Posts: 556 Location: Vancouver, Canada
Hello Jleb,
Tourmaline with totally occluded C axis generally is an awful colour, olive drab being the most common. Other than Chrome which is the same colour in every direction, any that have desirable colours have the best colour down the C axis which of course produces the smallest stone possible.
Some say Mother Nature has a sense of humour but I believe she is laughing at us not with us.
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