I’m in a bit of a quandary about cutting some emeralds for a
geologist friend who brought them back from Brazil. They’re a very
nice deep green color and almost clean, save for a few fractures.
These I think (without having done it yet) should pretty much vanish
after the stones are oiled.
The problem lies in the shape of the rough. It would yield quite a
large stone if I cut it so as to make one of the large flat sides the
table. But it would not be deep enough to get the proper pavilion
angles.
Standing the stone up on its side and using a narrow side as the
table will yield a narrow but deep stone, plenty deep enough to get
the proper pavilion angles. Yet a great deal of nice clear emerald
would be ground away (from the bottom) in the process.
“A” would yield a larger but shallow stone; “B” a smaller, narrower
stone but with proper pavilion angles and much wastage at the bottom.
What say you, gem-savvy Orchideans? How important are proper
pavilion angles in a nice deep green emerald? Which way of cutting
will preserve the most value?
Hans - Unless you’re exceedingly lucky with “jardin” there won’t be
enough internal clarity to get good refraction even with proper
angles all the way around. I don’t routinely work with emerald, but
my acquaintances who do cut for size and color. Perhaps we have an
emerald specialist who can advise more fully.
It is hard to give specific advice on such a stone without seeing it
as it is very difficult to know ratios of thickness and size that can
drastically effect cutting angles, but here are my views in general.
The pavilian angles are what causes primary reflection/refraction in
a stone which manifests as brilliance. Few emeralds (beryl) give this
effect as RI is only in the 1.5-1.6 range. Therefore you are cutting
primarily for color (and weight)! A lot depends on the
hue…blue/green, green/yellow, etc, and color saturation of the
stone. If it is a good even and deep color …cutting proper pav
angles (assume you mean 43 deg) will preserve the deep color but do
little to increase brilliance anyway. Reducing the pav mains towards
the critical angle, somewhere around 41 deg, will tend to lighten the
stone, do little regarding brilliance but you run the risk of
windowing the stone.
If the stone is a good as you say, I would stay with the weight, but
keep the pav angles as high as you can. You might be able to make up
some depth by increasing the crown mains a bit. This will preserve
some of the color as well.
You are luck to have an opportunity to work with a good emerald!
Cheers from Don at The Charles Belle Studio in SOFL where the rains
have hopefully stopped for a breather and where simple elegance IS
fine jewelry! @coralnut1
Hans, I would cut for the largest stone possible. Your goal is to
get the best stone out of the rough. The best stone is the largest
stone with the most brilliance. Grind your table over the largest
and cleanest portion of the stone. Dop to the table. Cut two main
pavillion facets until they meet at 40.0 degrees which is .5 degrees
above the critical angle. Girdle the stone while estimating how much
stone you will need above the girdle for the crown. Design other
facet arrangements for the pavillion that are above 41.0 degrees. I
use several arrangements of scissors facets. These facets do not cut
deep into the stone and are 1.5 degrees above the critical angle for
beryl. You will find that at only .5 degrees above the critical
angle most light will be reflected at a perfect 90 degree viewing
angle. Move your head slightly off from 90 degrees and you will see
a window. Scissor facets at 41 degrees will reflect more light when
you move your head and decrease the light leakage. Keep the end
facets at a sharp angle and step cut them. I would use the steepest
angles possible for the rough. Using this design you can often get
20-30% yield on a poorly shaped piece of rough.
What say you, gem-savvy Orchideans? How important are proper
pavilion angles in a nice deep green emerald? Which way of cutting
will preserve the most value?
Depending on how much you stray from the critcal angle (39 deg 21
min) the stone’ll develope some windowing. The greater the windowing
the more the appearance of color will be adversly affected.
Which affects the value of a stone more is hard to determine. I’d
prefer a well cut stone to a big stone assuming the differences were
reasonable.
Howdy Hans, As you say, its difficult to make suggestions not
handling the rough. One issue to always consider is putting your
mind into avoiding the obvious ,like searching for the table first.
Try to consider where on the stone the closest shapes are for a
pavilion preform, then, among those possibilities, what is the best
girdle outline. I’ve found in the past that what looks like an odd
rectangular form will best make a pear, triangular or somewhat
freeform shape if I consider placing the table where a corner is
now. If you rotate your rough so that a corner ispointing down you
may see a pavilion suited for a pear with a girdle outline almost in
perfect position, all that is required is to ‘sacrifice’ a corner to
create the table (even that may not be so bad if one corner of the
rough is less well formed than others, or you’re willing to cut apex
facets).
Another possibility, if the saturation will alow it, would be to
use ‘barion’ style cutting for the ‘deep pavilion’ position. Even
still, rotating the rough to position the ‘edge’ towards the bottom
will give a nearly preformed pavilion and wider stone (frome one
edge across to just under the opposite edge/girdle position).
You may need to actually 'think outside the box' on this<g>. Get
some rectangles of wax, make some pieces that approximate the shape
of the rough, and test 3-4 approaches to preforming, then weigh the
results. If this is a ‘significant’ project, it may not be
unreasonable to test cut 2-3 pieces in Laser Gem or other synthetic
and share the possiblities with the client. In actuality the
expectations of the customer/market for a traditional 'emerald’
shape (cut corner rectangle) may force you to waste material. But
you could conserve weight AND give you’re client a truly unique gem
by searching for the culet first, then the girdle position
-depthwise- and letting the table fall where it may.