Issue No. 104 - Wednesday April 9, 2003
Moderated by: Thurmond Moore III
Committed to carrying on the fine works of
Hale Sweeny and Jerry Dewbre
From the Moderator: 

Topical Focus for This Week: TOURMALINE CUTTING CLINIC

Lets get those post in for tomorrows digest.
Anyone have any favorite performance cuts?

Index to Today's Digest

01  RE:  Faceting crystal opal?
02  NEW: Depth guidelines
03  RE:  Faceting crystal opal?
04  RE:  Faceting crystal opal?
05  RE:  Tourmaline Cutting Clinic
06  RE:  Tourmaline and Opal
07  RE:  Cutting Fire agate
08  NEW: Appreciative Guru seeks GemCAD Wizard...
09  RE:  Tourmaline Cutting Clinic (stress in tourmaline)


Subject: Re:Faceting crystal opal?
Date: Tue, 8 Apr 2003 16:08:47 -0700
To: faceters@caprock-spur.com
From: Phillip L Stonebrook <plstonebrook@juno.com>

Greetings list and Dan...

Thanks for the kind words on my faceted blue crystal opals. For
convenience of the list members that wish to view them, use the link


Let me explain the rough selection and cutting process that produced
these 2 gems. A friend made a buying trip to Coober Pedy and returned
with several cases of quart canning jars full of opal rough. One day at
our club shop, we screened 72 quart jars and picked out approx 30 pieces
of rough that looked like good candidates for faceting. Of those 30, only
4 or 5 produced nice gems, with the 2 best shown in the above link - talk
about rarity!

The rough was basically the same as regular "jelly" opal, bluish orange
in body color, except they had a luscious blue opalescence mixed with
very small pin fire appearing out of the middle of the crystalline
material. After screening the mix of rough and working with the inferior
pieces first, it became apparent that the "best performance" that could
be obtained was for them to be cut so that the opalescent sheen would
flood the crown. The SRB in the link above exhibits this ideal, with the
Cardinal cut coming in as a close second. I BOG'd these designs to
maximize this inherently low optical performance material, with the PM's
coming in between 43.7 to 45 degrees; the CM's all came in at 41 degrees
(sorry Gustavo, I was in error earlier about PM/CM's of 43/35). I cut the
remaining pieces in a marquise and freeforms with the same angles - these
other finished gems and the rejects went back to my friend, since I cut
on rough "shares". The cuts were determined for best retention of rough
shape/weight. Cutting and polish was uneventful and straight forward. All
were cold dopped with CA to 5 minute epoxy.

In comparison to the fire opal I've cut, all characteristics were the
same, and all cutting and polish was again uneventful and straight
forward. So, if you've cut fire opal, give your mostly transparent
crystal opal a try with the same light handed cautious confidence you
would use with any precious brittle material.

Gustavo sent me some pix of a piece of crystal opal he has, and his
material has far more fire appearing in the rough, both broad and pin
fire. It was more translucent than my rough, but appeared to be more
transparent than "normal" white cabbing opal. For material like this with
more translucency and intricate internal fire, I suggested a cabochon
approach rather than faceting; possibly your suggestion of a simple
faceting approach might work Dan. Certainly, you would want something
that wouldn't interfere with it's play of color. I'm not sure about the
"tablet" approach, as rough this precious creates a certain amount of
"pucker factor" during experimentation. I recommended an expert opal
cutter's evaluation for the best outcome. I have seen rough like his
before, cabbed in a buff top antique square design and mounted in a deep
"sheltering" custom ring. It was majestic!

Best regards.....
Phil in Florida

<<Subject: Faceting crystal opal?
<<Date: Sun, 6 Apr 2003 20:42:27 -0400
<<To: Faceters and Lapidary Digest <faceters@caprock-spur.com>
<<From: Dan Clayton <dclayton@speakeasy.org>
<<Someone pointed out Phil Stonebrook's faceted crystal opal on the
<<www.qualitygemcutting.com site. The two I saw were beauts. Does
<<crystal opal cut any differently than fire opal. I would have assumed
<<fire opal would make a much better faceted stone than crystal opal
<<but these two are fantastic. I would have thought a tablet with two
<<opposing tables and a faceted girdle would be great for crystal
<<opal with it's play of color. It looks to me like you might want a
<<simple design that didn't overpower the play of color. Any comments
<<form our gurus?
<<Dan Clayton


Subject: Depth guidelines
Date: Tue, 8 Apr 2003 21:09:42 +0100
To: usfgfaceterslist@yahoogroups.com, faceters@caprock-spur.com
From: Michael Hing <post@maiko.demon.co.uk>

We all know there's a limit to how shallow you can cut a stone and still
keep acceptable performance (i.e. don't get too close to the critical
angle).  But how deep can you cut a stone?*  In other words, what's a
good guideline figure for how high the pavilion facets can go in
practice and yet still keep a "normal"-looking stone?

The reason I ask is that I've become increasingly aware that I've been
cutting to "textbook" angles all the time, and in some cases my rough
has been quite expensive and it would have been worth trying to salvage
some extra weight.  Previously I've only ever done this by cutting a
thick girdle, but I think it makes sense to cut to slightly deeper
angles on expensive rough, as long as I don't go so deep that the stone
starts to look bad.



* assuming that the rough is thick enough to allow it, and also assuming
that the stone is light in colour and isn't going to get too dark


Subject: An Opal by any other name, would surely smell as silicaceous...
Date: Tue, 08 Apr 2003 18:34:08 -0400
To: faceters@caprock-spur.com, tom@boghome.com
From: "Douglas Turet" <anotherbrightidea@hotmail.com>
Cc: herbst@mpia-hd.mpg.de

Tom Herbst wondered:
"Incidentally, I would have called this a Contra-Luz Opal, and Dan
Clayton / Phil Stonebrook refer to "Crystal Opal," while Greg Glenn
calls his a "Mexican Fire Opal." Anyone else confused?"

Hi Tom (and other mystified cutters),

     There seems to be a good deal of confusion on the various varieties of
Opal, so I'm-a just-a gonna have-ta add to it! (Or maybe diminish it,
depending upon what others have to offer, along the way.) The way I was
taught (by an Aussie Opal miner) was that "Jelly Opals" are those with
glassy clarity and relatively little (or no) play of color, such as the
smoky-yellowish materials from Lightning Ridge most of us have seen, with
the faint, smeary purple 'fire'. (Envision a congealed blob of apple jelly,
and you've pretty well got the idea.) At the other extreme, "Full Crystal
Opals" are those which have so much fire that you're all but blinded by
them, but which, when placed on top of a printed page, prove to be
transparent enough to seem "crystal clear". "Semi-Crystal" Opals are those
varieties whose bodies are slightly more cloudy than Crystals, yet not as
opaque (or faintly translucent) as White or Grey Bases.
     "Contra Luz" is another animal, altogether: it's a very specific type
of Jelly Opal which, though found primarily at the Queretaro field, in
Mexico, is found in other locations, as well. What makes "Contra Luz" so
special is what it does (or doesn't do, depending upon the perspective it's
viewed from) -- and the 'dead giveaway' about this is the English
translation of its name from  Spanish, "The Opposing Light". With a good
piece of Contra Luz, what appears to be a lifeless piece of Jelly Opal (when
viewed from above, with a light source above the viewer's head), can
suddenly explode with either the "Rolling Flash", "Rolling Straw" or "Rain"
patterns of fiery play-of-color, when lit from the side of the stone, 90*
away from the overhead direction. Again, hence the name.
     If I were asked to appraise these stones for insurance purposes, having
seen both Greg Glenn's site and Dan Clayton's, I'd call Dan's "a highly
translucent Semi-Crystal Opal with blue-green pinfire", and Greg's "a
colorless, transparent Jelly Opal with brightness level #5  Contra Luz
play-of-color in a red-green multicolor Rolling Straw pattern, very possibly
of Mexican origin". What's most impressive about Greg's piece is that it
appears to feature a complete lack of bodycolor, in the image at top right.
(Aside to Greg: am I correct in assuming that this shot was taken under
fluorescent lighting, which tends to deaden all things optically related?)
As for the nomenclature used, Greg's may very well be a Mexican stone, but
it is definitely *not* a true "Fire Opal". The reason that I can state this
with such absolute certainty is that the *sole* characteristic which earns
an Opal its designation as a "Fire" Opal is that it's coloring matches one
of those found in a fire: reds, oranges or yellows. Thus, just as a White
Opal cannot be a Black Opal, and an Aquamarine cannot be a Heliodor, a Fire
Opal cannot be colorless. So Tom, in the final analysis, you would have been
right-on-the-money to call this a Contra Luz Opal! (Woo-woo! Way to go,
Tom!!!) Okay, I think *somebody's* got too much time on his hands, today...
back to ye olde grinding wheel!

All the best,

Douglas Turet, GJ
Lapidary Artist, Designer & Goldsmith.
Turet Design
P. O. Box 162
Arlington, MA 02476, U.S.A.
Tel. (617) 325-5328
Fax: (928) 222-0815
Email: anotherbrightidea@hotmail.com


Subject: Re: Crystal Opal
Date: Tue, 8 Apr 2003 18:41:59 -0700
To: faceters@caprock-spur.com
From: Phillip L Stonebrook <plstonebrook@juno.com>

Greetings list...

Thanks Tom, for the link to Greg Glenn's faceted opal - it's very, very
nice! Go, look, see (one more time) at:

You also said: <<Incidentally, I would have called this a Contra-Luz
Opal, and Dan Clayton / Phil Stonebrook refer to "Crystal Opal," while
Greg Glenn calls his a "Mexican Fire Opal." Anyone else confused?>>

while Doug Turet also jumps in to sort out the confusion, and has
confused me even more with his wealth of experience, by mentioning things
like << .. especially one with #5 red-green multicolor .. If she's a
Semi-Crystal or Full Crystal .. cutting Contra Luz .. "Om me lapidary
hum..." As seriously twisted as ever ..>> Hahahaha!

Doug, since you obviously have the experiential expertise that makes your
recommendations worth listening to, why don't you think about
contributing to a "faceted opal clinic" after the tourmaline clinic, and
sort out our confusion! I know I would benefit! (I've thought about
complimenting you for your knowledgeable posts in the past but didn't
want to "pump up" your head .. too much {:>)!)

How about it Thurmond? (Yes, your header question on dark tourmaline is
the same "white paper limit" ((over 50-60% saturation)) test which we
discussed in the "dark garnet" clinic, with the same limitations, ie, cut
just above CA, or maybe below, with shallow crown, 2 bounce limit, and
large table to get light into/out of final gem. Cutting the table perp to
the "C" axis probably would be even worse).

Best regards...
Phil in Florida


Subject: tourmaline
Date: Tue, 08 Apr 2003 16:52:17 -0600
To: lapidary@caprock-spur.com
From: Steve and Nancy Attaway <attaway@highfiber.com>

Dear Faceters,

  About two and a half years ago, I purchased a wonderful 6.87-gram,
grass-green tourmaline crystal that was long and slim. I faceted it into
an emerald cut gem with step-cuts both pavilion and crown. In order to
maintain that fabulous color, the short sides of the emerald cut
pavilion, facets 24 and 72 on a 96 gear index, were cut at 80 degrees as
one pavilion facet each on those short sides. The resulting gem
exhibited great color. The finished tourmaline measured 34.5 x 8 mm and
weighed 18.58 carats; good recovery.

   For those lovely Nigerian tourmalines (liddicoatites), I have used
very shallow pavilion angles, like those used for sapphire, and even
shallower for those deeply saturated stones; culet angles at 40 degrees
or even 39 degrees. The shallower angles brightens the color and
enhances the sparkle. A good polish is rendered on a corian lap with
diamond and a ceramic lap with diamond, but other faceters have polished
this gem material with linde A on a tin lap with very good results.

   I am posing a question for you folks with a lot of chemical
knowledge. Does the presence of manganese and bismuth affect the
hardness of a gem? I ask this, because I have noticed how much harder it
is to polish morganite (versus aquamarine) and some of the Nigerian
liddicoatites (versus the tourmalines from Brazil).

  Nancy Attaway


Subject: Re: Issue No. 103 - Tuesday April 8, 2003
Date: Tue, 08 Apr 2003 16:02:23 -0700
To: LapidaryArtsDigest <lapidary@caprock-spur.com>
From: Noel Rowe <noel@roughtocut.com>

Hi Thurmond & list,

> Lets get some comments on cutting of both open and closed "C" axis
> tourmaline.

Open axis tourmaline can be treated like any other stone when cutting.
It can be oriented either on the AB or the C axis, which ever gives the
best color. One thing that can be nice is tourmaline's dichroism. Some
is stronger than others. If you have a piece which is fully open on the
C & strongly dichroic, it can yield a very nice stone. An example of
this can be seen at my site at
http://www.roughtocut.com/Cut/Tourmaline.htm ,Item#Trmsf01c. This was a
piece of seafoam tourmaline with a nice aqua/green color on the AB & a
yellow green on the C axis.

Closed axis tourmaline should be cut in emerald, rectangular bar cuts &
rectangular cushion cuts as long as the ends are cut at 68-70 degrees.
If you try to cut an oval, trilliant or round pattern in a closed axis
tourmaline you will end up with a very disappointing dark stone. Some
semi-closed axis stones will work well in trilliant & apex type cuts but
if it's fully closed don't try it. A good example of closed axis
tourmaline can be seen at http://www.roughtocut.com/Cut/Tourmaline.htm ,
Item#Trmi02c. This indicolite had a very dark C but was cut with the
ends at 70 degrees.

As far as the white paper test goes Jeff Graham has an excellent
explanation on his website at:
Generally if you are looking at the stone in good light (not spot lights
or halogen lights) the color you see is going to be close to what you
get. A good bright cut optimized for tourmaline like an apex cut or a
bar cut will sometimes brighten the stone a bit, but heavliy saturated
material is just not going to let much light through.( That's why with
closed axis tourmaline you cut the ends on the C at 68-70 degrees to get
them out of the line of site.)

> Incidentally, I would have called this a Contra-Luz Opal, and Dan 
> Clayton / Phil Stonebrook refer to "Crystal Opal," while Greg Glenn 
> calls his a "Mexican Fire Opal." Anyone else confused?
> Tom Herbst

Hi Tom, I'll weigh in on this one.

Mexican fire opal has a body color ranging from yellow/orange through
red. The classic Mexican fire opal is cherry red. The "fire" in the name
doesn't refer to the play of color (opal with a play of color used to be
referred to as "precious opal") rather the term "fire" refers to the
body color. And "Mexican" refers to the country of origin. So even
though opal from Oregon here in the USA or the Lambina fields in
Australia may share the same characteristics they are not Mexican fire opal.

Crystal opal is a bit more nebulas in it's definition. It depends on who
you ask. An opal dealer may try and sell translucent opal (sometimes
called "jelly opal") as crystal. True crystal as the name implies is
crystal clear. Usually (but not always) exhibiting a play of color. the
brighter & more distinct the color & the clearer the stone the more
valuable the opal. Mexican opal can be crystal opal or jelly or opaque.
Australian, American & Brazilian opal also can also fall into those

The term "Contra Luz" refers to the type of color play. In almost all
opal that exhibits a play of color the color usually only shows best in
reflected light. In contra-Luz opal the color shows best in transmitted
light (light coming from behind the stone). Often under normal lighting
the color will be faint & washed out if visible at all. But hold a good
piece of Contra-Luz up to the light & it will come alive with color.
Contra-Luz can be spectacular when faceted because the facets can take
the light & reflect it back through the stone.

If this isn't confusing enough there is also Black, semi-black, gray &
white base opal - all referring to body color, all can be either
crystal,  semi-crystal (jelly) or opaque. Then there is Hydrophane
(crystal when wet, opaque when dry). Boulder opal - thin coating on
non-opal matrix, Ironstone, Yowah nuts & koriot opal (all varieties of
Ironstone - opal veining or kernels in a rusty to black matrix). Matrix
opal - white to buff colored sandstone cemented with precious opal
usually treated with sugar & acid to turn the body color black.

Hope this clears it up.

Rough To Cut


Subject: Re: Fire agate
Date: Wed, 9 Apr 2003 01:41:54 -0700
To: lapidary@caprock-spur.com (LapidaryArtsDigest)
From: Tony <lightbender@thegemdoctor.com>

Hello Pauly,

I haven't cut much fire agate recently but I did work through a
few pounds in the 70's.  Good light is essential, I dragged my
Crystalite Ringleader into the garden and cut by sunlight, Yes
we do have sunny days in Vancouver. Following the humps and
curves should be kept to a minimum as deep clefts are hard to
polish. I used the edge of my diamond wheels to achieve a
curvature which could be easily polished with the edge of my
polishing pads. Remember to allow for sanding loss as the
colourful limonite (Hydrated Iron Oxide) is microscopically

As with Opal the brightness of colour play and the extent and
uniformity of coverage is the major portion of the value with
purple being the most desirable colour.

HTH. Tony.


Subject: Appreciative Guru seeks GemCAD Wizard...
Date: Wed, 09 Apr 2003 13:29:20 -0400
To: faceters@caprock-spur.com
From: "Douglas Turet" <anotherbrightidea@hotmail.com>

Hey gang,

     (No, that's not the opening line for a personals ad, it only *sounds*
that way!) I have a question/challenge for all of you GemCAD wizards, out
there... In the September, 2001 issue of the USFG newsletter (Vol.11, No.
3), on p.29, there's a revised of a cut by Ernie Hawes, called "The Winter
Queen". My question is whether one of you could possibly re-revise this cut
such that the side mains (P2) would also be SHM's, just as the end mains
(P6/P8) are. While that might require a shortening of the center (P7) mains'
height and a lengthening of the side breaks (P1), I'm thinking that it'd
both increase the finished stone's volume from 0.299 to about 0.34-35 (thus,
increasing weight retention), simultaneously boost overall brightness by
6-10% and improve the "implied coloration" (by increased retro-reflection)
of the finished gem.
     (Oh, yeah, and it'd sure improve the looks of this 11x14mm chunk of
Aqua that's sitting in front of me!) With that in mind, is there anyone on
the list who'd be willing to help me realize this goal? How's about this for
an incentive: I have a pastel peach Malaya Garnet rough here (that looks
like it'll cut about a 1 ct. finished gem) just waiting for the first person
who's able to accomplish that for me. For that matter, is Ernie Hawes a
member here, himself?

All the best,

Douglas Turet, GJ
Lapidary Artist, Designer & Goldsmith
Turet Design
P.O. Box 162
Arlington, MA 02476
Tel. (617) 325-5328
eFax (928) 222-0815


Subject: Stress in tourmaline?
Date: Wed, 9 Apr 2003 11:13:51 -0400
To: Faceters and Lapidary Digest <faceters@caprock-spur.com>
From: Dan Clayton <dclayton@speakeasy.org>

Hello faceters,

Since we are discussing tourmaline this week what "tricks" do you
use to identify stress in tourmaline. I have had a couple tourmaline
that appeared to be flawless or nearly so develop cracks during
cutting. I assumed it was stress in the crystal being released. Is
that the most likely possibility? What clues do you look for before
you start to cut tourmaline? I have thought about using my polariscope
to look for stress but haven't followed through. Suggestions? I bet
I am not the only one with this problem.

BTW Gustavo has a couple new designs posted under 77 index designs.


and I have two new designs under star designs at


Ray Gaetan posted a photo of a Bytownite he cut in Gustavo's First
Dawn design. First Dawn is on Gustavo's design page also the photo
is here:


Dan Clayton









PERSONALS: (General Lapidary and Faceting)




Lurking is fine, but participation is better for learning !
Post something from your experiences in gemcutting today!


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