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Light entering faceted stones


#1

Orchidians, In regards to the discussion we were having about how
to bring out the best in cab stones, there was mention about setting
faceted stones so light can enter the pavillion (bottom) to
supposedly enhance the brilliance of the stone.

I tried an experiment, I took a large  peridot, aquamarine, rose

quartz, and a small diamond into a dark room, used a penlight and
held it on the top of the stone and then behind the stone with me
viewing it from the top. I saw little or nothing I could see as
refraction or reflection from any of the stones when the light was
behind the stone.

I believe what I did made it pretty clear to me that the optic

principles that I understood were indeed true. Light entering from
the top of a stone, and if faceted to correct critical angles, light
returns back thru the table and crown facets to the observer. Light
entering from behind has virtually no effect.

 It also makes me aware that some of the misthe public

receives is coming from the people who make or sell jewelry and
gems. Stones are being set with an open back for the purpose of
having light enter from the back or side of the stone, and it isn’t
going to do anything to help. It will make it easier to clean, which
is a benefit.

There has been statements about the people who buy jewelry not

knowing enough or not caring enough to make wise choices. Based on
some of what I read on this board, they are being supported by
incorrect and personal prejudice to be the way they are.
When someone asks a question, do we tell them we don’t know or do we
make something up? Do we take the time to get educated for that next
person?

Most jewelry is sold through mass merchandisers and  salespersons 

who are just earning a living. There is no passion for what is being
done, it is just a money making machine. They advertise to tell the
public what to buy. They create the desire for what they sell. The
sales person doesn’t know anything more than what is written on the
price tag.

Being involved with jewelry, the making of it and the sales can

bring someone into areas that are very technical, and I experience a
lot of myth and old wives tales. There is a tremendous amount of
to learn and if you are self-taught, the truth for me is
that it takes a long time to get a resonable foundation of knowledge.
In Europe there are standards for making jewelry, technical
standards and design standards and titles that are earned based on
skill and knowledge. We don’t understand or value those standards.
Appentices there just file for two years and cannot do their own
designs. They follow a system. You have to be a part of the system to
get a job. You have to meet an established criteria.

If you are stringing beads, there is not that much technical

If you are making a custom wax, casting and setting it
and selling a natural unheated aquamarine in a ring with diamonds,
you better know what you are doing for when that piece is appraised
in the future, it better be what you said it is. Jewelry is probably
the most emotional object that our society values. The symbology of
wedding rings, whether the first marriage or the third. Ruin your
customers dead mothers ring, break a treasured stone,ect and you
will be acutely aware of what it means to your customer.

I have been obsessive compulsive about learning as much as I can so

I have credibility, and after 30 years I still learn something new
every week. I am overwhelmed at times, there is a tremendous amount
of liability we have when we work with the public in retail.

The level of knowledge we should aquire should be relational to the

amount of responsibility, and the consequences that we would suffer
from not knowing what we should.

How can we establish a criteria for how well made a piece of

jewelry is when we have no standard of training for goldsmiths, and
our system of quality control seems to be the length of time the
customer can wear it without damage.

I got that out of my system! What do you think?

Richard in Denver


#2

Hi Richard, I won’t discuss you considerations about business.
Concerning the light entering the stones, I bring your attention on
two points: - when photographing stones, I often noticed that the
facetted gemstones don’t look the same way whether there is a white
background or a black one. I may be wrong, but according to my
experiments, I am sure that, in the case of clear facetted
light entering from the cutlet enhances the appearence of
the stone (as long as the stone isn’t too weak in color). -
concerning the cabs, as only low end qualities are cut into cabs,
they very often are hardly translucent, and not transparent. The
reflexion of the light only occurs in the very first millimeters
under the surface, and the light coming from the cutlet doesn’t seem
to cross the cab. But i read that some big and thick cabs were cut
with a concavity in the cutlet to seem more vivid. Unfortunatly, I
never saw any. Yann www.webcarats.com


#3

Richard and others,

Richard reminds me of a problem we all have – faulty memories!
You think you remember something correctly, would perhaps even swear
to it, and are horrified to discover later – after you’ve told
others – that the is incorrect. We can probably all
think of some instances when we’ve done that – I know I can! (My
readers are usually kind enough to point them out!)

I’m lucky: I have editors. When I write something for a magazine,
there is at least one, and frequently two or three people between me
and the reading public. Heaven knows I do my best to keep incorrect
from sliping by me. But it does happen: perhaps I was
dead certain I was remembering it correctly and a deadline was
looming, so I forewent a fact-check, or perhaps I misunderstood what
I was told. Most of the time, one of my editors catches my error
before it makes print. (Boy, do I hate it when a mistake escapes all
of us and gets into print!)

The rest of you are going direct to your public, without the safety
net of editors that I have. That means sometimes you will make
mistakes, and relay incorrect Like me, you try to be
careful, and it doesn’t happen very often. This is different from
intentional deception, where you tell someone something you know
isn’t true, or something you made up because you didn’t know the
answer. In the cases I’m thinking of, you thought you knew the
correct answer.

It’s not that we’re ignorant or uncaring. We’re just human. We make
mistakes. So let’s cut each other a little slack, if only to the
extent of correcting gently!

Of course, when I screw up, I can let my readers know through a
published Correction in another issue. What do you guys do? Is there
a jewelry-selling equivalent of a Correction?

Suzanne

Suzanne Wade
writer/editor
Suzanne@rswade.net
Phone: (508) 339-7366
Fax: (928) 563-8255


#4
How can we establish a criteria for how well made a piece of
jewelry is when we have no standard of training for goldsmiths,
and ...

Indeed, Jewelers of Amarica (JA) has set such standards and
administers a series of tests to judge the skill levels of th e test
taker. All the people I’ve ever seen who attained Master are
awesome…just awesome. Now that doesn’t mean you have to be JA
Certfied Master to be awesome, but…those that have the
designation ARE.

Wayne Emery


#5

My experience is that when a stone is faceted to correct critical
angles, what is behind the stone does not have any effect. I have
shown this to my customers over and over. Think of a correctly
faceted stone as a mirror. Does a light behind the mirror have any
effect? There is a tilt angle that will allow light to pass thru
from the back. It does not appear to me to have the desired effect of
reflection or refraction that is what makes a stone attractive. If
you look at a windowed stone, it usually looks good around the edge
where the crown facets are, but washed out color and no brilliance
thru the table. On a windowed stone table horizontal to something
with printing on it, you can read the print. With a properly faceted
stone held with table horizontally to the paper, you can not read the
print. If a windowed stone is set with an open back, you can see
the skin of the person wearing it. With a properly faceted stone, you
cannot. At least this is what happens in my world. Richard in Denver


#6
    Indeed, Jewelers of Amarica (JA) has set such standards and
administers a series of tests to judge the skill levels of th e
test taker. Wayne Emery 

Hi Wayne; I agree that the JA’s bench certification program is a
welcome development for our industry. It provides three things, I
think;

  1. The public has a way to determine if the jeweler they are
    thinking of having work on their jewelry or make jewelry for them can
    do a good job.

  2. An employer has an idea of the skill level that he can expect in
    a certified jeweler.

  3. The certified jeweler has a way of representing and verifying his
    skill level, and he has a credential he can advertise.

What I’d like to see is JA develop some guidelines as to what level
of compensation a certified jeweler might be able to expect from an
employer. Employers feel very threatened by jewelers being aware of
what they can bargain for in the employment market. (I’ve been told
I would be fired for discussing wages with my fellow employees . . .
I wonder how that would go over in an unemployment compensation
hearing . . .). It’s taken me years to get an idea of what I can
expect to be paid, and I’m now very forthright about sharing that
with my fellow jewelers, just as employers certainly
discuss among themselves what they pay their jewelers. The secrecy
about wages among jewelers has contributed, in my opinion, to the pay
of jewelers being among the lowest of the skilled trades and
subsequently, we have a serious shortage of skilled jewelers. Of
course, the availability of inexpensive overseas labor markets has
helped, as have immigrant populations who can be exploited here. I
wonder if JA would be supportive of national or even international
unionization of jewelers.

David L. Huffman


#7

Howdy Orchidians, Here’s a little test some of may be able to
perform. We must begin by trying to define a ‘well cut stone’. If
the ‘main pavilion facets’ (on some cuts this is hard to define but
is almost always the collection of facets that form the culet point
or edge or line) are cut at angles that fall roughly between the CA
(critical angle) and .333333 times (180-CA) for the gem material in
question, very little light falling on the ‘backside’ of the stone
can be refracted out the front.

	In practice, most careful faceters will select/create/modify cut

designs to yield main angles which are 1-3 degrees above CA. When a
stone’s main pav. facets are cut ‘too shallow’(at or below the CA)
you get ‘windowing’ or ‘fish-eyed’ stones. Most folks consider that
a poorly cut stone (except perhaps for very dark garnets or some
other criteria REQUIRING an effort to bring light in from the rear).
The other extreme, too ‘high’ (steep,deep) angled main pav. facets
are often found on ‘belly cut’ stones. Remember that many (often
foreign) cutting houses will place a somewhat greater emphasis on
recovery (carat weight) and ‘calibrated size’ than brilliance and
,while sitting under bright lights in a case almost all stones look
dazzling, the human eye is ‘saturated’ with ‘dazzle’ and the true
performance of a well cut stone may only be noticed in
’office’/‘grocery store’/‘intimate’ lighting conditions. Nowadays
few folks are wearing their nice stones in full daylight.

	Back to the test. If you can get examples of the 3 categories just

mentioned, a belly cut stone, a fish-eyed stone and a well cut stone
proceed as follows.

	The fisheyed stone is easy. take a scribe or even your finger and

pass it back and forth behind the stone. You clearly notice large
images/shadows moving around directly under the table. There will
probably be smaller reflections distributed around the crown as well
but the main ‘problem’ is the too shallow pavilion angles. This is
often what happens to beryl/quartz and other low RI materials when
they get some skin oils on them. Look at a well cut quartz that is
very clean. Now rub a little ‘nose grease’ on the pavilion and note
the difference. Due to a narrow difference between the CA and
1/3(180-CA) low RI stones are most severely affected by oils or
other contaminants this way. CZ ,diamonds etc. can still look pretty
good when dirty.

	Now let's take a 'well cut' gem. Use a scribe or narrow probe and,

while looking at the right side of the crown, move the scribe up and
down while holding it just over the left side of the crown. You will
see the refracted image of the scribe’s shadow move around (mirror
image mostly) on the opposite side of the stone. This proves that
most (not all - more later) of the light entering the stone is
falling onto it’s crown. Now, if you get too close, there can be a
problem we call ‘head shadowing’ and some otherwise nice looking
stones do not ‘accept’ light from a very broad ‘cone’ around the
crown, but in general they still are better than the other 2
’categories’. If you extend the scribe all the way to the center of
the table, the refracted images should still be seen. If you perfrom
this test with the fisheyed stone you probably WILL see the scribe’s
image in the break/main/star facets (because they plus the
pavilion’s BREAK facets may be at ‘working’ angles) but you will not
see the image refracted by the facets under the table. The light is
’falling through’ or we could say only light entering from behind
the stone will enter the eye from the fisheyed table.

	Now, something just a little different is happening with the

‘belly cut’ stone. Light rays entering the pavilion facets from the
side but down at an angle (let’s call it 45 degrees, but it’s a wide
range in reality) are making one ‘bounce’ off the opposite pav.
facets and exiting the table to land in your eye. In a well cut
stone most rays enter the crown (top) are bent slightly, bounce off
2 facets and exit the crown (bent slightly again) hopefully headed
into the eye. So, move your scribe around the side (and perhaps down
a little) of the pav. of your ‘bellycut’ stone and notice
reflections of the scribe through the table. They will most like ly
be on the pav. facets OPPOSITE the side on which you are moving the
scribe.

	Here are some caveats (actually cover my a**<g>). There are 

many
types of cuts cut in many ways in many materials. Some cuts are
notoriously poor performers (optically) though they may sometimes be
chosen for reasons of tradition (‘emerald’ cuts) or style
(navette/marquis). Even many ovals perform poorly in low RI
materials. The best way to do the above tests would be with SRBs in
a medium RI low dispersion material - say - white sapphire. But,
some ovals may be OK to use. though, when we call a cut 'poor’
performing we mean it has low brilliance DUE TO EXACTLY THE REASONS
STATED ABOVE!. Too many ‘areas of extinction’ where a light ray
would HAVE TO enter the stone from the girdle or the back to arrive
at your eye! Most jewelry either has limited openeings in the back
or is worn such that the opportunity for significant amounts of
light to enter the back is nil.

	I alos apologize if using terms like up and dowm ,top, back etc.

are confusing. I really am using my hands to show you! I hope
someone will try some of the tests and see if they are helpful. Do
keep in mind that, considering their pay scale and equipment,
foreign cutters do a good job. And if the incentive were shifted a
little more to brilliance (which I believe it has in the last
decade) than recovery, it would be a noticeable improvement. The
more you educate your selves, the more they will respond to demnads
for better cutting. Carl 1 Lucky Texan


#8

All, Most of the knowledge available lays out in great detail the
physics and mathematics about what a “well cut gemstone” should look
like. There are definite physical limits to the way that light can
be bent. refracted, and perceived by the eye. Computers can readily
model the cuts and give you a good idea of what the finished stone
should look like. From this point on I have many disagreements with
what is called a “well cut gemstone”. I see many stones that are
award winners that have very little practical use in jewelry. To me
an award winning stone is an art and not always a well cut stone.
Gemstones do not come out of the ground in neat little preforms all
ready for someone to enter the dimensions into a computer, out pops
the perfect cut for that stone, and a person dops the stone and a
"well cut gemstone": Gemstones come out of the ground in irregular
shapes, with no color, clarity problems, dichroism problems and many
other variables. Each and every gemstone has many different ways in
which it can be cut, but only a very few that yield the best result
for that stone. My goal is to produce the best gemstone I can to be
fashioned into metal jewelry. That means that I have certain
restrictions about depth, clarity, color, girdle, and crown. I also
must fashion a gemstone out of the rough that has enough weight
retention to make the stone economically feasible to cut. It does me
no good to cut a $200 piece of rough into a $150 gemstone. If the
gemstone rough will not cut a perfect stone then I have to manipulate
the cut and cutting to produce the best economically feasible stone
that the rough can produce. That is where a cutter makes money. The
most important cut on the gemstone is the table. Where you place the
table will determine all the rest of what you see in the stone. A
stone with a properly orientated table will look many times better
than a stone that has an incorrect table orientation. Everything
else that is ground on the stone will be determined by how much stone
is under the table. Individual facets depth, placement of those
facets, and polish are not near as important as orientation.
Orientation can not be modeled in a computer. Knowledge, experience,
and skill determine the orientation of a well cut gemstone. My idea
of a well cut gemstone is not what everyone can make. Go by a
Gemcutters booth at your next gemshow. If they have 25 of their own
art stones and 500 stones cut in Asia you may be impressed by the 25
art stones. Go by a Gemcutters booth that has 1,500 of their own
stones all that, are bright, colorful, and easily set into metal and
you are looking at a Cutter that knows how to cut a “Well Cut
Gemstone”.

Gerry Galarneau
www.galarneausgems.com


#9

David Hoffman and All, I would support Unionization of all related
fields in the jewelry industry. That would include gemcutters,
casters, bench jewelers, sales persons, metal producers,and anyone
else associated with the jewelry industry that does not own a shop.
Unionization would insure that uniform standards of performance and
training apply, safety standards would be enforced, definitions
would be clarified, and illegal fringe activity would be diminished.
For the first time the workers in the industry would have a say in
how the industry dealers treat the workers. The jewelry dealers
(store owners and other sellers) and gemstone dealers would be forced
to deal uniformly with the group that makes their living.

Gerry Galarneau
www.galarneausgems.com


#10

Dear Fellow Orchidians, Concerning our discussion about light
entering a gemstone: JCK has an article in June 2002 on Diamond
cutting “Tolkowsky Revisited”, following is a paragraph directly
lifted from the article:

Cowing credits Bruce Harding as the first to determine “where each
point on the diamond gets its light and then researching and
mathematically determining pavillion and crowm angles which avoid
light’s being drawn from the observer’s head or from below the
gemstone’s girdle.” Harding’s work was published in an article
entitled “Faceting Limits” in the Fall 1975 issue of GIA’s Gems and
Gemology.“This work has had a significant impact on the design of
optimum angles for cutting colored gemstones,” says Cowing.

As to my prior postings I am grateful for support that was

serendipitious, gemstones can be cut that do not allow light to enter
from the pavillion for maximum enhansement of the qualities that make
a gemstone beautiful and desireable to the person viewing the stone,
assuming you set them right side up… Of course not all gems are cut
to this criteria. Hopefully this will help those that purchase gems
to learn to tell the difference. It will make a difference in selling
their work, theirs will stand out against the competition in my
opinion. Mine does.

Richard on a rainy day in a very dry Denver


#11

Unionization has about the same chance as a snowball in hell.
Unionization doesn’t insure performance or training or the other
aspects you mention. Sorry, but that’s my $.02.


#12

Dear Gary, Galarneau’s wrote:

    I would support Unionization of all related fields in the
jewelry industry. 

With all due respect, from just one person who spent nearly twenty
years of his life working on both sides of the mighty UAW, I’m
wondering what world you live on, because it’s not based on reality.
The very best thing that can be said for most unions is that they
were a necessary evil, and most union people will admit that the
majority of their efforts go to helping bad employees keep their
jobs. I have so many horror stories I could tell on this subject,
but this is not the time or place for that.

Jewelry mechanics have one thing always on their side, and that is
freedom of choice as to where they work. If an owner takes advantage
of you, pack up your tools and move on to the next job, and yes,
there are more jobs out there for the good worker. Incompetant
workers look for someone to protect them, to force management to
reward them for their lack of effort exactly the same as the good
worker. Always remember the 90/10 rule. 90% of your problems will
come from 10% of your work force, and without unions, that 10% would
never be able to keep a job.

Jon


#13
    Unionization has about the same chance as a snowball in hell.
Unionization doesn't insure performance or training or the other
aspects you mention.  Sorry, but that's my $.02. 

Hi KP and others; Unionization isn’t about performance or training.
. . that’s what certification is for. Unionization is for collective
bargaining. So JA could certify and the union negotiate wages and
agree to satisfactory standards of performance.

David L. Huffman


#14

I have only set 8 stones before and I have a question about
reflection/refraction. The first two stones I set were glued with
clear finish epoxy. The result was terrible. When the stones were
loose and I looked at them through the table there was plenty of nice
reflection. If all that reflection comes from light entering the
table why does the glue in the setting, which is below the table,
cause the stone to be dull?

I have since graduated to gypsy and prong setting. While the
reflection is improved, it still is no where near as brilliant as
when the stone is loose. Is that normal or what am I doing wrong? I
have seen toy jewellery out of vending machines with better
brilliance than what I am getting.

Thank you,
Jim Millius.


#15
   I have only set 8 stones before and I have a question about
reflection/refraction. The first two stones I set were glued with
clear finish epoxy. The result was terrible. When the stones were
loose and I looked at them through the table there was plenty of
nice reflection. If all that reflection comes from light entering
the table why does the glue in the setting, which is below the
table, cause the stone to be dull? 

Dear Jim, As one after another answers this, the same answer will
be, you have changed the pavillion of the stone by adding the glue
to the back. You changed the critical angle. Most all of the light
will now go right through the stone and not return to the eye of the
beholder. When you say you are setting the stone, my opinion is that
setting involves using some metal: prongs, bezel, channels, not
glue. Occasionally under special circumstances, glue is used, but
only a tiny bit at the girdle, to kep the stone from moving around
when hammer setting.

Richard in Denver


#16
     When the stones were loose and I looked at them through the
table there was plenty of nice reflection. If all that reflection
comes from light entering the table why does the glue in the
setting, which is below the table, 

Dear Jim And All, You have started to understand one of the most
complex problems in facetted Let me start to explain
what happens to light in a facetted gemstone. By our new standards
a perfectly cut gemstone is one which returns the most light that
enters the stone through the crown to the pavilion facets back
through the crown facets to the viewers eye. Sounds pretty simple.
Making this a very complex subject is the fact that all light that
enters the top of a gemstone does not enter a perfectly
perpendicular angle and that most gemstones are not very uniform in
structure. This means that when that light is bent inside the
gemstone (refracted) its angle upon which it strikes the facet is
often below or well above the angle at which reflection can be
maximized. What a mouthful. Light that does not enter the gemstone
at a perfect angle is partially reflected and partially escapes out
the back of the stone. Complicating all this is the fact that each
and every gemstone absorbs light. That is what produces the
perception your eye views as color. On one end of the visible
spectrum of light is the color white on the other end is the color
black. When you see white you are seeing almost a total reflection
of the light beam with very little absorption. When you see black
you are seeing almost total absorbed light and very little
reflection. The escaped light is the problem. Escaped light makes
for less than total reflection. When this happens anything behind
the facet is struck by the light. The same process above happens
again. Some of that light from the escaped light reenters the stone
from the back. Yes, light enters a stone from every angle,
including the back. That is why you can often see the mounting.
This new light has been absorbed and reflected by the new object
changing its wavelength. Thus your eye has quite a job analyzing
and presenting to your conscious this blend of wavelengths of light.
This is called perception and is a quality of anything that uses
light to visualize.

How do you get around this problem with facetted First
buy gemstones that have a uniform color and the most brilliance. If
you do not want the metal to change the color mount the stones in
white metal. Mount the stones with the table as close to
perpendicular to the viewing angle of the viewer as possible. For
cabachons I would always mount my stones in a closed back bezel of
white or silver metal that I had polished inside as brilliant as I
could polish it. I would never mount a crystal cabochon in an open
back mounting. In Kurt Nassau’s books on color he has a very
complex graph which shows the relationship of blending wavelengths
of light to the color perceived by the human eye.

This is a short discussion and I have left out many of the details.
Do not take my word for it. Read Kurt Nassau’s book he is the
expert I am just a stone cutter.

Gerry Galarneau
www.galarneausgenms.com