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Cabochon Backs: Polished or Unpolished


#1

I have a question I would like addressed by jewelers who use
cabochons in their work.

Under what circumstances should the backs of the cabochons be
polished?

I can think of two which are when the cab is used in an open back
piece of jewelry and when the stone in clear enough so that saw
marks are visible from the top.

Are there other reasons for the backs of the cabs to be polished?

Larry E. Whittington Lapidary
http://www.jewelrycabs.com


#2
I have a question I would like addressed by jewelers who use
cabochons in their work. 

I think you have set with some certain opinions. I don’t set many
reasons why you would clean up the back. Etching it a question of
rocks. If it is see through then choose what you do. I don’t see
many choices where a grubby background is good.

I hope this helps,
Philip


#3

Hi Larry

The backs of cabs may be polished if the pattern is really nice, as
on a well banded or patterned agate or jasper. Then we also would
have an open backed setting so as to show it off.

Regards
Karen Bahr - Karen’s Artworx
Calgary, Alberta, Canada


#4
Are there other reasons for the backs of the cabs to be polished? 

There is one other reason that I can think of, and that is pride of
craftsmanship.

A cutter who pays attention to every detail of a piece is taking
care to do his best, even if he has to charge slightly more. For the
same reason, I may, myself, decorate the back of a brooch or the
inside of a ring.

A cab that incompletely polished limits the design possibilities for
its use, and signals that the cutter was cutting for speed, not
quality.

Noel


#5

Larry, your comments of when to polish a cab back are very on point.

My thought is that a polished back shows a greater pride of
workmanship. when I cut a cab I will almost always polish the back.

the main exceptions are when I know I will be glueing a cab into a
setting for a customer I want that roughness to help the glue grip
the stone. the only other time that I can think of for not polishing
the back is when I am cutting a replacment stone to match others in a
repair when the backs are exposed and not polished.

well that’s my 2 cents, I hope it’s worth it.

Jerry


#6

From a rockhead. Yes it is more pleasing and I always will buy the
polished then the unpolished.

Eric
www.ericsfinejewelry.com


#7

I have been cutting cabochons for 40+ years and teaching lapidary
for 12 years and I always polish the back and bevel the back edge of
the girdle regardless of the material. It is a reflection of my
standards for craftsmanship. If the girdle isn’t beveled on the back
edge, the cabochon is always susceptible to chipping, especially
during the jewelry fabrication and setting steps. If the stone is to
be set in any level of quality jewelry, I would think polishing the
back and beveling the girdle would be the standard of acceptable
quality.

The run of the mill, standard cut ovals of average quality are
finished by tumbling them in a rock tumbler. If you look at the back
and it has an inward dish, it has been tumble polished.

If you are purchasing higher cost and quality stones they should
have a pleasing shape, have no fractures or pits, have no visible
scratches, have no mini flat spots and have the featured pattern to
be prominent and colorful.

To check for the absence of mini flat spots (or a flat top) stand
under a flourescent light with the stone’s long axis going right to
left and the flourescent light bulbs going the same direction. Rock
the stone towards and away from you and look at the reflection of
the individual bulbs on the surface of the stone. If they flutter or
open and close as you rock the stone then it is poorly cut.

To check the quality of polish, hold the stone under a 100 watt
clear (not frosted) incandescent light. Again look at the
reflection. It should reveal any scratches present.

If you see any then again it is poorly cut and polished.

If you spend considerable time crafting your jewelry piece you
wouldn’t want a poor quality stone to represent the overall quality
of the piece.

Bob Rush


#8

Hi Larry,

Are there other reasons for the backs of the cabs to be polished? 

I’ve heard it said that matrix opals are best with polished backs
(reduces the porosity of the ironstone or sandstone matrix; increases
stability). Otherwise, no reasons I can think of (as long as the
sitting edges of the cabs are beveled). Oh, one other possibility:
they look better polished, which may make them easier for the stone
cutter to sell.

Beth


#9

When talking about polishing the back of the stone and beveling, it
depends. I should amend that. I can think of no exceptions to the
need to bevel the bottom edge to prevent chipping.

As far as polishing though, while many stones lend themselves to a
relatively easy polish, others don’t. The most obvious and
consistent exception would be opal because of the highly variable
nature of how it grew in it’s matrix. Of course standard white opal
of relatively cheap and uniform rough will be relatively easy to
polish and finish off on the bottom, but many many opals will simply
not allow for an easy finish to the back. Obviously, if the stone
will be set with prongs, then it does need to be smoothed on the
bottom but a large number of opals will not allow for a smoothly
finished bottom. This is certainly true with most boulders as well
as many blacks. I’ve been cutting lightning ridge for days now and I
can say that I consider it far better to leave a thicker more stable
stone than try and completely even and smooth the bottom. Often
these stones are nearly as much carved as they are cabbed.

As far as other stones are concerned, there may be reasons not to
polish the bottom completely. Jadeite for instance is difficult to
polish especially on a flat so it becomes very time consuming to
polish and it can also be irregular because of chips or etc.

The final reason not to finish the bottom completely is cost. Some
people would prefer to pay less rather than have a polish on an area
of the stone they never intend to show after it’s bezeled. I think
we should always work with people on this sort of thing.

Derek Levin
www.gemmaker.com


#10

Hello all, this is my first post,

in response to Derek’s post I would say that another exception to
polishing the back of a stone is in the case of turquoise.

I collect and sell rare, natural turquoise and find that leaving the
back of a stone unpolished helps to identify the stone as natural,
untreated material.

Thanks very much!
Mary


#11
I collect and sell rare, natural turquoise and find that leaving
the back of a stone unpolished helps to identify the stone as
natural, untreated material. 

How does it do that? Treated material can be left unpolished too…

Noel


#12

Hi Noel!

I wrote,

I collect and sell rare, natural turquoise and find that leaving
the back of a stone unpolished helps to identify the stone as
natural, untreated material.

And you asked,

How does it do that? Treated material can be left unpolished too...

When a turquoise stone is left unpolished, or uncut, you can see
into the “vugs”, or crevices in the stone, (if there are any). If the
stone is untreated these vugs will not be filled in with epoxy, or
with whatever treatment is used. Also if the stone is untreated
whatever “motherstone”, or “matrix”, is showing, (if any), may be
seen as being a different texture than the turquoise, for instance
the
motherstone will frequently be softer than the turquoise around it.

This is one way of helping to detect natural from unnatural
turquoise, a lot of it is from experience though. I have looked at
thousands and thousands of pieces of turquoise by now and have a
pretty good idea of what to look for.

Thanks for asking.

By the way, I have a LOT of incredible, natural material for sale,
both High-Grade turquoise and High-Grade coral. I would post pictures
if I knew how, maybe I’ll try and figure that out soon. Please feel
free to ask questions or to ask for pictures, my email address is
@M_G

I have what is referred to as “fossil” turquoise as well. It’s not
true fossil stone but actually a “fossil replacement” of fossilized
clams that were replaced by the minerals that make turquoise, thus
making “fossilized turquoise clams”. This turquoise is from the
Carico Lake turquoise mine. They are also know as "Pseudomorph clams"
and are EXTREMELY RARE.

If anyone has any advice on where I could sell this material please
let me know, I have too much of it to ever use.

Thanks all!
Mary


#13
I collect and sell rare, natural turquoise and find that leaving
the back of a stone unpolished helps to identify the stone as
natural, untreated material. 

There’s a much simpler way to detect treated turquoise: use a sewing
needle or straight pin; heat it and touch it to the suspect stone in
an inconspicuous spot. If you smell resin you’ll know. Whether to
polish the back or not is a matter of aesthetics. A well cut stone
will have the edge chamfered, as someone has already pointed out, to
prevent chips. Polishing the back indicates attention to detail and,
this is purely personal, makes for a more attractive stone.

I’ve bought many stones, finished and rough, and much of it is
slipshod. I buy cut stones. I look at them as preforms. I’ve rarely
bought one that I didn’t recut. I don’t know how jewelers who aren’t
lapidarys deal with the problem of poorly cut stones. Most cutters
don’t have a clue about setting stones. Well cut stones are difficult
to sell since most consider the price as the most important factor.
So it’s a more limited market.

KPK