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Doc's Corner
HOME
On this page we want to answer your questions and
give you some information about opal. The topics will be up to you. If there
is something that you would like to see addressed here by all means ask. Send
us an email.
Weighing Opals
Many people seem to be confused about weighing
opal material. So we would like to give you a little bit of information that may
clear up this issue for you.
Opal is weighed by troy ounces not the avoir du
pois ounces that we commonly use in the United States. So, if you are buying an
ounce of opal from us, it is a troy ounce of opal which is 31.1 grams. Rough opal in
large volumes is sold by the kilogram (1000 grams). As the value of the rough
increases, the rough is sold by the individual gram or percentage of a gram.
Increasingly, here is the U.S., mostly because of the auctions, relatively inexpensive
rough opal is sold by the Carat. There are 5.0 Carats in one gram.
It is interesting to know that the
"fire" areas in opal are actually quite light in weight so that pieces with more
fire and less potch may weigh less for the same "volume" of rough.
As a summary we will list some of these
equivalents below:
1 kilogram = 1.000 grams
1 troy pound = 12 troy ounces
31.1 grams = 1 ounce troy
1.0 gram = 5.0 Carats
By way of comparison to the avoir du pois system
that we commonly use, we offer these comparisons:
1 kilogram = 2.2046 lbs. avoir
1 ounce avoir = 28.35 grams (notice this is LESS
than one troy ounce)
16 avoir du pois ounces = 1 avoir lb.
If you have trouble with the millimeters
and grams you can use a Java converter by going to the Liz's Corner Page of this web site.
There is a handy link that will load the converter for you instantly. Then use the length
or mass conversion requests and locate the millimeters or grams and the inches or ounces
and it will automatically do the conversion for you. Click the link below to try it for
yourself.
Cabochons
There is no doubt that the question that we get
asked most often is about various types of cabochons. We will answer those questions
below in a glossary form.
Glossary
CABOCHON - is a piece of any
material that has been cut to set into jewelry that is not a
faceted stone. Cabochons generally have a flat bottom, slightly slanted (10 to 15
degrees) sides and a flat or domed top. They can be freeform or calibrated in shape.
This cabochon is a freeform.
CALIBRATED - calibrated cabochons
are created to allow the use of manufactured settings ( i.e. 6 mm x 8 mm, 8 mm x 10 mm,
etc). A lot of really valuable opal is cut freeform to make use of every tiny
bit of available rough. Custom jewelers frequently prefer freeform cabochons for
their custom design work since freeforms are an earmark of a individually created piece of
jewelry. Appraisers give more value to the oval and calibrated shapes, however. And
calibrated cabochons fit manufactured jewelry settings.
CHIP INLAY - chip inlay involves
epoxying tiny chips of opal material (Or any other lapidary material) into a cell in the
jewelry piece and then smoothing the surface with ordinary polishing methods.
Gilson Opal Chips
DOUBLET - doublets are a thin layer
of opal epoxied or glued to a usually black opal base. Sometimes other materials
like ironstone are used for the backing, but opal purists believe that the only acceptable
thing to use and still call the creation an opal is black opal potch. The doublet
allows use of good opal material that is too thin to act as a stand alone solid
cabochon. A doublet can be more valuable than a solid opal depending on the quality
of the rough used for each.
This is a doublet.
Here is a side view of a doublet. Enlarge
the photo and you will be able to see the distinct two layers of the stone.
This is an ironstone backing for a doublet.
Other materials are also commonly used for backing materials including black potch, black
jade, and onyx. At the bottom of this page we show the steps involved in making a doublet.
FREEFORM - as the name implies, the
shape of a cabochon in any form or shape. It is up to the jewelry designer to decide
how to incorporate the freeform stone into a piece of jewelry.
This is one of an infinite number of shapes that a
freeform stone can take. Freeform stones are an earmark of custom made jewelry since
they will not fit calibrated settings.
GILSON - Gilson opal is man made
opal material and can be quite showy. There are other varieties of man made opal on
the market as well.
This is a photo of a Gilson black opal. As
you can see they can be quite dramatic.
INLAY - opal inlay involves
epoxying "cut-to-fit" pieces of solid opal material into chambers in the jewelry
piece. The ring below is a manufactured setting with four chambers to accept inlay.
Doc did the inlay work.
This is some of the jewelry of Lexi and Bern
Sundell who are quite skilled inlay artists.
Photo by Bern Sundell, it is used with permission.
INTARSIA - involves epoxying
"cut-to-fit" pieces into a patterned design on a backing material. The
intarsia example below was created by Tracy Smith, a talented intarsia artist.
Photo by Tracy and Lisa Smith and is used with permission.
MOSAIC - a mosaic cabochon is like
a triplet in construction except that the middle of the sandwich is composed of many tiny
pieces of opal allowing even the smallest piece of colorful opal material to be used.
This is a mosaic opal triplet.
TRIPLET - a triplet is an opal
sandwich with the opal material being the center material. Black opal potch is the
preferred backing and clear quartz the cap of choice. This is another way to use
colorful opal material that would otherwise be too thin for a solid cabochon.
Triplets can be more valuable than doublets or even solid opals depending on the quality
of the rough materials involved. This is one way for someone to have a very colorful
piece of opal that would otherwise be extremely expensive. The little triplets like
the more that we sell that were made in Australia are thin slices of opal that are
actually sliced by a machine. The machine can also be set a little thicker to slice
the backing material as well. The cap can be flat or domed, but if domed the cap
when viewed from the side is clear.
This is a photo of five little triplets.
These are one type of triplet where the clear covering actually encompasses all of the
opal with the black backing material fitting into the top cap. If you enlarge the
photo and look carefully at the stone on the lower right, you can see the clear covering
on the left side of that stone as it encircles the stone.
This is a view of a triplet of the type above from
the back side. Look for the clear edge encircling the black base for this type.
Another type of triplet is represented by these
photos. In this type the clear top sits on top of the opal layer and in this case it
is a high dome clear top. The top would not have to be so high.
This one has a high dome clear top, a black base
and a thin layer of opal material in between. The visible color in the high dome is
a reflection of the color below. The dome is actually clear. Like the clear
dome below.
This is a black base like the one used for the
triplet pictured above.
Doublet Construction
As an example for a contest for The Opal
List, we are going to show the construction of a doublet in a series of photos.
We are starting with the black backing
material and the opal layer.
We are using a piece of black opal potch
for our backing material. This piece has been ground flat on the flat lap, but has
been left with a 600 grit finish. The shape of the piece is just the shape that it
happened to be and has nothing to do with the anticipated finished piece.
Doublet tops
We chose a couple of pieces of Lightning
Ridge in thin pieces that we thought would yield a blue coloration over the black base.
One of the pieces, once ground off, had
too many sand inclusions to have to deal with for the amount of color that it would
yield. These little spots can be removed with a diamond bit with a Foredom, but
unless the opal material is really special it is not likely to be worth all of the
trouble.
The second piece proved to be more
promising.
There are some small inclusions that can
be avoided in the final cabochon. One side of the piece was left at 600 grit and the
other was polished to a high shine with 50,000 diamond compound.
The slice is set on top of the black
backing material to help locate potential problem areas.
Wetting the backing material makes the
problem areas even more evident.
The inclusions show up quite well when the
pieces are wet along with scratches on the 600 grit surface. We determine that
additional polishing of the bottom side of the opal material will be necessary and that
the inclusions may need to be worked on with a diamond bit. before continuing. It is
also evident that the black backing opal needs to be flatter so it will go back onto the
flat lap as well.
This is a view of the top and backing, both are
wet, after they have been "flattened." The two fit more closely together
now. We also worked on some scratches that remained on the top of opal piece.
The two photos above are two views of
the top with the back darkened with a Permanent marker to show me where the problems area
are located. I use this method because I can easily remove the marker.
I can also permanently color the back with paint (like Testor's enamel as Paul Downing
advises in his book). I was able to determine that I had plenty of clear area to
create the cab that I wanted. After this step I glued the two pieces together using
Epoxy darkened with soot from a candle flame collected on a metal lid. I mixed the
Epoxy in the black soot to color it black. The exposed black edge that you can see
in the photo below is of the black epoxy on the black base material.
This line shows the cab that I want to cut out of
the
assembly.
Here it is the finished doublet.
This view shows the side construction. It is
important the thin opal material not be the part of the assembly that sticks out the
furthest. Stress in setting can cause the thin opal slice to break if it catches the
brunt on the setting stress. Many doublets have both tops and bottom than are much
thinner than these two pieces. Since I am making this one to suit myself I made a
high cab which is the way that I like for them to look.
To Be Continued
SUGARING PROCESS
Please note that any treatment of this
kind to any lapidary material MUST be disclosed. If you employ this treatment to any
opal material or other lapidary material, you are required by Federal Law to tell any
potential purchaser that stones have been treated/stabilized.
Andamooka
Before
After
Canterras
Before
After
Honduran
Before
The after photo of the Honduran is not here, but
it does not look any different. I will post it at a later time.
Epoxy Treatment for Stabilization
Please note that any treatment of this
kind to any lapidary material MUST be disclosed. If you employ this treatment to any
opal material or other lapidary material, you are required by Federal Law to tell any
potential purchaser that stones have been treated/stabilized.
We are frequently asked questions about stabilizing opal.
It has also been a topic of discussion on The Opal List from time to time. We
have decided to work with Hxtal Nyl (which is a register trademark I am sure) because we
like what we are able to do it. We have included some photos below that will
hopefully show some of its potential uses.
The photos below are of some very friable opal matrix rough
from British Columbia. There are a few little flecks of play of color in this
material, but we were not worried about showing them in the photos. This material
was also first sugar/acid treated to blacken the matrix. The material after the
treatment is quite hard. We will also show the cut opals when that step has been
completed.
Before
After
This next set of photos is a piece of Mexican Cantera Opal
rough. The photo on the left shows a crack in the rough before treatment and the
photo on the right shows a photo of the rough after treatment. You can see that the
epoxy has actually been absorbed into the matrix because the rough actually looks wet in
the areas where the epoxy was applied. We get a lot of Mexican Opal rough that is
cracked because of their mining methods. Some of those pieces are quite colorful and
might well benefit from this type of treatment.
Before
After
The next few photos deal with some cut opal cabochons from
Mexican Opal rough. There are three different cabochons in the photos. The
first one shows before and after views. The second two show after views. In
all of these notice that it will be necessary to go back and smooth the top of the
cabochon. The epoxy "puddles" on the top of the stone, but in the case of
the lower two photos has completely filled voids that were in the top of the cabs.
All of these cabochons have been sugar/acid treated previously. Photos of all of
these appear above in the series of photos on the sugar/acid treatment.
Cabochon I
Before
After
After
Cabochon II and III
Notice the puddles of epoxy on the surface that will require
that you go back and repolish the surface of the cabochon.
The cabochon below is a piece of Quantum Quatro Silica (which
is also a registered trademark). This material is very prone to cracks and
fractures. Many of the blue, green lapidary materials need to be stabilized in some
manner. This particular piece has a quartz crystal on the surface and a
fracture that runs away from the that. You will probably need to enlarge these
photos to see exactly what I am talking about.
Before
After
We are also showing two cracked opals that are in a ring that
came in for repair that we treated with this material. The owner of the ring
is quite aware that the opals with ultimately need to be replaced, she was just interested
in prolonging the life of these as long as possible. Both of the opals are severely
broken. That is they are both cracked into two pieces. The only reason they
are in the ring at all is the tension of the mountings that is holding them together.
The lower one is in a better position to benefit from treatment than the upper one
because the upper one has actually shifted position and the two halves no longer exactly
meet. We also did not heat the opals as the manufacturer of Hxtal Nyl recommends for
fear of risking any of the other opals that are at this time intact. The cracks did
not disappear after treatment though the lower one was certainly considerably less visible
and the upper one slightly less visible. The true test of whether this was a worth
while effect will only come with time. If the stones falls apart next week, I would
say that it was not worth the trouble, but that remains to be seen. In time the
opals will need to be replaced and then the trick will be to find rough that will cut
opals that will "fit in" well enough with the ones that are already in the ring.
We are asked frequently about repolishing rings with opals in them that
have become scratched over time. We do this type of work, but we work at the
customer's risk. We cannot guarantee the results. We do not take the opal out of the
setting because of the great risk to the stone and/or the setting. The photos below
show two before and one after photo of a Mexican Opal ring that we recently reworked .
We considered the project a great success.
Be sure and look at the enlarged photos to get the full picture.
Gold Rush Jewelry, Bead and Art Company
P.O. Box 635
Fairplay, CO 80440
719-836-2143
719-836-0831
You are welcome to call us. These numbers ring at our home and studio which are
located in the same place. Just place your call at some reasonable hour for our time
zone which is Mountain Time in the United States. You may also contact us by email
at any of the addresses below.
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