Administered by Hale Sweeny (

This list digest contains the following message subjects:

1. LapDigest News for Issue #24, 7/13/97
2. NEW: Sugilite Rough
3. NEW: Storing Opal (Was- Change in Opal Colors over Time)
4. NEW: Carving Mexican Opal
5. RE: Carving Mexican Opal
6. RE: Tumble Finishing Cabs with a Vibrasonic Vibratory Tumbler.
7. RE: Bulk Slabbing of Nodules
8. RE: Sawing with a Fence
9. Re: How do I saw a base at an angle?
10. RE: Polishing Mother of Pearl
11. RE: Polishing Mother of Pearl


Subject: LapDigest News for Issue #24, 12:11 AM 7/13/97

Some personal news about our members:

If you have had trouble getting in touch with Mark Case <MarkCase@aol;.com> recently, here's the reason. Mark writes:

"My wife had an emergency c-section on Wednesday and delivered our son, Micah Lee Case. He was 5 weeks premature and will be in the Neonatal ICU for about two weeks. He is having some problems regulating his breathing (For all you statistics buffs: he was 6 pounds 4 ounces, 18 inches long, blond hair, blue eyes and feet wide enough to walk on water!)"

Congratulations to your wife and to you, Mark. And we hope and pray your son is doing well.

. and Ken Wetz <> writes: "

Yesterday my credit card company informed me my credit card had been
compromised. It seems a hacker broke into an online computer system in
California ..... and stole a number of credit card numbers. ..... he attempted to sell them to an FBI agent who arrested him. ..... and I will
get a new card shortly. Reason I bring this up is the company I did business with is one I'm sure many of you might also do business with if you buy rough ,...(snip)... Just thought I'd let folks know this type of thing happens. Ken

..and Saturday is (or was) Bll Figi's birthday! <>


Date: Sat, 12 Jul 1997 10:24:33 -0700

Subject: NEW: Sugilite Rough

At a recent rock show I was looking at a piece of sugilite rough. It had a
shiny appearance and the seller said he had rubbed it with olive oil. It
was the size of a large baking potato. Then he tells me it's a $200 piece
of rough and if I buy it I can cut $1000 worth of cabs from it. I'm new to
lapidary but this was too much blarney for me. I walked off. But it made me
think. Is rubbing rough with olive oil an acceptable practice or is
something being hidden? Is sugilite rough that expensive? And finally he
said this sugilite had some "rick....." (can't remember the specific name)
mineral in it that was a beautiful blue. What was that?



Date: Fri, 11 Jul 1997

Subject: NEW: Storing Opal (Was: Change in Opal Colors over Time)

One of the original questions was whether to store opals wet or dry. I
vote dry. (here in Arkansas some of us vote dry and drink wet, but that is
a different election). All opal has the capacity to hold a considerable
amount of water (not just hydrophanes).

Back when the Lapidary Journal contained lapidary articles, it carried a few on opal. As I remember it, opal is made up of zillions of microscopic spheres. Water is wicked up deep into the interstices between the spherules and is retained for a (long) time. The internal water affects both optical (color play) and mechanical characteristics of the opal. Some of us have had opal crack or craze when it is dried out. In my experience, this doesn't happen often.

I think a proclivity for breaking up is a function of opal type and origin.
Cracking may be due to internal stresses set up by areas of differential
moisture content. For this reason I have a theory that dry opal is less
heat sensitive for dopping. At any rate, it is better for problems to
happen before cutting than after. Perhaps opal is sold in water bottles
in the first place because (a) the colors look better, (b) the pieces look
much bigger than they really are, and (c) any drying damage will happen
long after the sale. Perhaps not. At any rate, one of the LJ articles
recommended that opal rough be stored dry. Made sense to me so I have done
it that way ever since. I never cut a piece until it has "seasoned" for
several months. Good results so far and besides, you can't keep it wet

A long time ago I bought a few Mexican fire opal preforms out of a wet tub.
They all seemed perfectly transparent. I still have one of them because
when it dried out, I noticed a paper-thin layer of something semi-opaque in
the interior making it unsuitable for cutting. When you hold the opal just
right you can see tiny points of color in this layer. The process is
reversible: the layer disappears when the stone is soaked long enough. It
takes weeks to go in either direction.

I remember seeing ads for some sort
of non-drying solution (oil? plastic? cement?) to treat opals. Does
anybody know what it is and what it's good for? Does it just fill cracks
or will it soak into sound material? Is Opticon used this way? How long
must the piece be soaked? I haven't had much experience with Opticon, and
have only used it once or twice on friable materials.

I think those old Lapidary Journals (*) from the 60's, 70's and 80's are worth their weight in gold. I lost mine moving around the country. They were heavy but I have regretted it ever since. I keep looking at flea markets.

Sorry to have bent your ear for so long, Bob

(*) [Ed. Note: While not as good as having the magazines, you may buy the Lapidary Journal Index, 1947 -1991, an index of all papers published from 1947 through 1991. It is organized in several ways for convenient searching. When you find a paper you want, you can order a reprint from LJ for $2 each and $0.50 postage for each 5 reprints. (I think this is right!) The toll free number for LapJour is 1-800-676-GEMS, and their e-mail address is They do accept major credit cards in payment. The last batch of reprints I ordered took 10 days to arrive. Not bad! hale]
Date: Fri, 11 Jul 1997

Subject: NEW: Carving Mexican Opal

<<In her post on the change in opal colors, in Issue #23, Carol Bova asked, almost as a by-the-way question: "In the meantime, any advice on free form carving Mexican opal?">>

Advice, well, I finished a small carving in mexican jelly a few weeks ago.
In my humble opinion opal carves more or less in the same fashion as most other stones, only a bit easier. The condensed version is: I use assorted diamond tools for the rough carving, proceed to finned grits, down thru diamond polishes, and finish with tin oxde. If anyone is interested in the long version I will post it.

Best Wishes

(Ed. Note: I asked him to post the long version. hale)

Email adresses

Date: Sat, 12 Jul 1997

Subject: RE: Carving Mexican Opal

I used to see quite a bit of this material, usually packed in jars with
water, but lately the supply seems to have dried up, so to speak. Are
Mexican cutters accounting for more of their production, or has the export
of rough been banned? The best of it, to my taste, was the orange
translucent type with mostly green fire, but I also got some very small but
intensely colored stones which were clear with blue/red/violet fire. The
problem for free-form carving is the small size of all the rough that I've
seen. While the Mexicans solve this problem by carving it matrix and all, I
found the effect unconvincing. The matrix, while it polishes to some
degree, is somewhat sandy, even crumbly, and I wouldn't like to have to set
it. I've never had any problems with delamination or crazing as the stones
dried out- they seem stable enough in our (California) climate, but maybe
I've just been lucky.

Andrew Werby - United Artworks
Sculpture, Jewelry, and Other Art Stuff

Date: Sat, 12 Jul 1997

Subject: RE: Tumble Finishing Cabs with a Vibrasonic Vibratory Tumbler.

(This is an answer to questions raised by Vince King <> in
LapDigest #23)

I have always gotten better results with 2/3 to 3/4 capacity loads - I
can control the rotation better with my tumbler at these levels. The
action controls the tumbling better.

Knobs Lapidary - Kentucky agate cabochons - designer cabochons in Kentucky
red and balck agate - other types of materials from all over the world.

Date: Fri, 11 Jul 1997 23:42:55 -0400

Subject: RE: Bulk Slabbing of Nodules

In Digest #18 (msg3), I outlined the gist of embedding a rock in High Early
Portland / Acrylic Latex using a Plexiglas (or Lexan) variable-sized mold to
produce a saw-friendly "cube". This technique is faster and stronger than
plaster of paris embedding.

In Digest#20 (msg 7), Vincent had some further questions:

>I'm assuming here that this additive will be found in the Paint section? One
>of the other difficulties with the process I use, is the losing of the end
>cuts, which more often than not are a little more than end cuts. The gist of
>your formula leaves me with the impression that the nodules to be cut will
>literally be "glued" into the matrix. Have you experienced a significant
>loss of end cuts during the cutting process, or do you find that these hold
>in place regardless of shape? Without exception, all of the Snake Skin
>nodules that I cut are very much smooth and rounded detracting from any
>adhesion properties that would normally exist in a surface that is uneven.

Acryl-60 is a professional level product and should be found where High
Early Portland cement is sold. We have a building supply yard where bulk
sand, brick etc is available where it is sold by the quart, gallon, 5gal (?
55gal drum). Sometimes a savvy DIY store will have it. The Thoro site
(mentioned by Hale) is excellent and has a
FULL data sheet (.PDF image) for Acryl-60 as a download option.

I leave 2" waste above the rock which is held in the saw jaws. I cut slabs
until the trace remaining is of no further interest. ALL of the rock is
available, encased in cement, extending beyond the carrier vise. The big
saw is an 18" Highland Park. I'm sorry I don't know the oil brand... it was
last purchased in a return deposit 55gal drum and was poured off into 5gal
pails which say "floor cleaner" or some such today.

I also cube out medium sized rock to be cut on a water cooled 10" Beacon
Star manually using a .040 diamond blade. For fine work, a 6" .012 LapCraft
Dia-Laser on a high speed Beacon Star will cut quite small stones embedded
in the same fashion... scaled down, of course, typically 1"x1"x3". Finer
blades work ok but I tend to be a fine motor klutz and too chicken to use
the .006 & .004 blades manually.

I suggest setting up a mold for just one of your nodules and giving it a try
with the formula I outlined. Be certain the nodule is absolutely free of
loose material as the Portland is moderately alkaline so tends to scour any
hard adherent clay or such. If adhesion is too low for you, step up the
ratio of Acryl/water to 1:2. If this is too low still, go back to 1:3 ratio
and after mixing the mortar and just before pouring make a "neat" mix of
pure Acryl and Portland which coat as a primer on the nodule. At 1:2, I
have some difficulty removing the cement "rind" from the slabbed piece and I
think you can get the bond "too good"!

Note that Acryl-60 is designed to interbond stone aggregate with portland.
For me, I just paint the rock with Acryl-60 when I place it in the mold. I
go on to mix the mortar so the coating is about tacky half-wet when I add
the mix.

>Opinion time. While building up the molds, what's the detraction from doing
>a dry stack inside the mold to evaluate quantity of material to be stacked
>and layout. Place the stones in the order to be fit inside mold. Mix brew,
>pour in enough to fill mold about 1/4. Dip future slabs into remaining
>solution to allow total coverage of material, then stack into mold as per
>laid out in dry run. Stack till stone pokes out of goo, pour more, stack
>more till container is full. This method would guarantee fewer air pockets,
>allowing better adhesion between forthcoming matrix and rock. What drawbacks
>do you see from this?

Sounds ok to me. But Portland firms up rapidly when not stirred and there
is an ultimate time of 10 to 20 minutes when the mix will stiffen too much
to handle.

A few further additions to my original post-

Fluid portion of 3-1/8 oz per cup of dry portland depends on packing... Have
extra Acryl/water mix available. A finished yield of 6-1/4 fl oz per cup of
dry portland used is also "ballpark" depending on packing.

I measure ingredients as well as the rock volume in fl oz. I measure the
mold in cubic inches and I use: fluid oz = (cubic inches)x(0.56) and cubic
inches=(1.8)x(fluid ounces) as conversion factors.

To determine the rock volume, I drop it into a can brim full with water. I
capture the spillage and measure the displaced volume.

To hold the plexiglass sheet sides in place while seaming with the hot melt
gun I use steel cubes and high strength magnetic buttons (rare earth
1"x1/8"...35Lb pull) pkg of 5 for $8.95 from Lee Valley Tools
1-800-871-8158, item 99k32.13.


Date: Fri, 11 Jul 1997

Subject: RE: Sawing with a Fence

>>From: (Msg4, Digest #20)
>>My question relates to the advisability of using a fence when slabbing
>>small agate nodules ( less than 2 inch on my 6 inch Rock Rascal) to
>>ensure a straight cut and constant thickness in the absence of a rock
>>I don't seem able to get constant thickness hand holding the stone and
>>have already dished one blade by allowing the stone to twist
>>inadvertently, I don't want to wreck another !

For the reasons you state, I embed small stones in a cubic matrix of
Portland/Acrylic for stability in sawing thin slices. Without further
comment here, I reference the ongoing thread- Re: Bulk Slabbing of Nodules

These two threads are intersecting with problems and good answers.

* George Butts, KC8T
* Laurie Butts, N8CKI

Date: Fri, 11 Jul 1997

Subject: Re: How do I saw a base at an angle?

>geri arms and hale sweeny
>This query is really about how to set up a piece to be cut in the vice
>Consider that I have a piece of stone say 4" x 4" x 6", from which I want
>to carve an object to sit on the 4 x 4 base, except that I want it to lean
>backwards at 15 degrees, say. What kind of jig or setup do I need to hold
>it in the vice of a slabbing saw to cut the base at the desired 15 degrees?

I do this by marking dots on the stone in three places to create a proposed
"sawing plane". These three marks will be parallel to the saw face. I mark
with bright fingernail polish for visibility.

At this point, please refer to the ongoing thread- Re: Bulk Slabbing of
Nodules ...with a new twist where a "pillar" of modeling clay is placed on
the plexiglas plate under the rock. For a stone of 4x4x6, I would suggest
about a 1-1/4" clay "blob" to support the rock. The rock is given a twist
to marry the clay to both the rock and the base plate.

Now, using a suitable measuring device such as outside calipers, the stone
is pressed and tilted such that each of the three marked dots become equally
spaced above the plate. The plate is de facto the plane of the saw. When
the three points are parallel with the base plate and all is stable, I fill
in as described in the other thread with Portland/Acrylic mix. I want the
Portland to fill the sides of the rock to the base plate but I generally
ignore any air under the stone and the supporting clay.

When the mold is taken apart, you will see the clay on the bottom of the
stone. Using a tool, remove the clay. You may have to chip away some of
the encroaching cured portland to do this. This isn't so important to the
saw since it will be in the waste zone anyway, but it's "crud" you really
don't want to add to the oil.

This is really easy to do but it gets tedious to try to describe. You're
just holding the stone in sawing position while encasing it in a "fixture"
made of Portland/Acrylic.

* George Butts, KC8T
* Laurie Butts, N8CKI

Date: Sat, 12 Jul 1997

Subject: RE: Polishing Mother of Pearl

In Issue 23, Hale Sweeny wrote:
<<A friend in Illinois wrote to me: "Do you know what will polish mother of pearl? I found some incredibly beautiful clam shells on the Mississippi
River .... (snip).... Someone told me there is a jeweler's polish of some sort that would make them really shine, but I don't know what it is. " Well, how about it, gang? Anyone want to help this lapidary neophyte by discussing any aspects of cutting and polishing shells?>>

It sounds like your correspondent found some of the Missisippi clam shells
that are used to make the beads which form the centers of cultured pearls.
I've worked with these myself, and found them a very attractive material in
their own right, with a color ranging from creamy white to a hot pink.
often arrayed in layers. It works readily with lapidary tools, either
diamond or silicon carbide, and I used Zam compound as a final polish,
achieving a high shine.

I found the hinge parts of particular interest, with an interesting sculptural form and a nacre rivaling that of most pearls, and have cut these out and polished the edges to make them usable in jewelry. Somewhere in Japan there must be some huge heaps of these, since this part wouldn't be useful for bead-making.

Does anybody know if these clams are still thriving there in the Big Muddy, in spite of all the exporting and pollution? Are the ones being used currently from live shells, or are they dredging up old deposits? Are they going to have to find a substitute soon in order to continue making pearls?

Andrew Werby - United Artworks
Sculpture, Jewelry, and Other Art Stuff

Date: Sat, 12 Jul 1997

Subject: RE: Polishing Mother of Pearl

Please be very careful when grinding and polishing shells. Most stones
give dust when ground, but shells can give tiny splinters (in some cases). Use lots of water in grinding and sanding and wear gloves (rubber dish type
are fine). Follow all the steps for stone polishing. You should have
some nice finished pieces.

Steve Ramsdell
+=+ +=+ +=+ +=+ +=+ +=+ +=+ +=+ +=+ +=+ +=+
Ed. Note: Sinkankas (Gem Cutting, 3rd Ed. p 338) notes that there are two kinds of shell: nacreous (Mother of Pearl or MoP) and porcellaneous. Porcellaneous shell is grown by the oyster and the common clam, among others, and is so much tougher and harder than nacreous material that it is treatred like a soft gemstone. Cut and preform with lapidary equipment; sands easily and polished with tin oxide, tripoli or Linde A on almost any kind of buff. For nacreous shell, typified by freshwater 'mussels' or 'clams' grown in almost every eastern state, use ordinary lapidary techniques but with care as the material is removed quickly. Do under wet conditions as dust may be poisonous to some people. Polish as with porcellaneous, but also use cerium oxide on leather. (It would seem to me that on this soft material, ZAM on a cotton buff would give a great polish.)
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