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This list digest contains the following message subjects:

1. LapDigest Issue No. 128 - Friday 3/27/98
2. NEW: The Future of the Lapidary Hobby
3. NEW: How Do You Make Opal Doublets and Triplets
4. RE: Another Motor Question
5. RE: Another Motor Question
6. RE: How Do You Cab Obsidian?
7. RE: How Do You Cab Obsidian?
8. RE: How Do You Cab Obsidian?
9. RE: Saw Oil and PCBs
10. RE: Saw Oil and PCBs
11. FS: Used Tumbler and Diamond Saw


Subject: LapDigest Issue No. 128 - Friday 3/27/98

This Digest is being published early, as we have received so
many postings for it. Even so, I have saved back 4 postings
for the next issue. (If you don't see yours here, it will be
in the next one!) Hope you enjoy this one - I really learned
a lot from it!

Please remember to add the words "non-commercial republish
permission granted", so that clubs, etc. can pick up items
for their club newsletters. And why not sign your name?


Subject: NEW: The Future of the Lapidary Hobby

Thank you for this very professionally prepared list. I
anxiously wait for each issue, and enjoy gleaning from the
knowledge of these fine list members.

The letter by Mr. Houk in #126 has finally prompted me to ask
this question. It was also a topic in the most recent issue
of Rock & Gem magazine. I too am 36, and around here that is
considered young for this hobby. I started at the age of 14,
when a group of over 30 retired rockhounds, changed their
by-laws to allow me to join. I received an education from
these people, that kept a young teenager focused on something
more than the options kids have today. The sad part is that
all but 8 are gone.

There have only been two new members added since 1976. The
other members are concerned about the club they started in
the early 50's. I remember what they did for me, and I want
to help keep this club open and going on.

What is the impression of the other list members, about the
future? What can we do more than placing books in the library,
helping host a show, giving short talks to schools, or
advertising in the newspaper?

Sorry this was so long, but your help and suggestions would
be greatly appreciated. Thank you.

Timothy Hill (Iowa)

non-commercial republish permission granted

Subject: NEW: How Do You Make Opal Doublets and Triplets


I am looking for information on making opal doublets and
triplets. If anyone has done these and can give me some basic
information, I would appreciate. I have several books but
none mentions specifics. I have a lot of nice material that
is thin but with a lot of color.

Any help would be appreciated.


Tim Vogle

Non commercial reprint permission granted
(Ed. Note: Tim, two issues were totally devoted to this some
time ago in which detailed methods were given. Send a request
for Issues 91 and 92, and Index3.txt, which you should check
for other references to doublets and triplets. hale)

Subject: RE: Another Motor Question

Hello Dixie,

You said you weren't sure what to call the thing which is
attached to the motor and which causes the bowl to vibrate.
How about calling it a weight or an eccentric weight.

They are weighted off center so that a vibration is imparted
to the motor and anything that is attached to the motor.
Frequently the weight is adjustable so that you can change the
amount of vibration by moving the weight 'out' (increase
vibration) or 'in' (decrease vibration). The bowl is then
suspended by springs to allow the vibration to be used to do
the work, the springs are all used to absorb the vibration
energy to keep the machine from "walking" around the room.

Hope that helps.

(Ed. Note: Thanks, Lester, for the explanation. I wish the
springs did keep my Gemstone vibratory tumbler from walking
all over - and off the bench .. I use it with stainless steel
shot for finishing metalwork, and have to use a 'dam' around
it to keep it on the bench!!! Anyone have a better solution?

Subject: RE: Another Motor Question

Several people have recently asked about sources for
replacement motors. The Grainger company has about 190 pages
of various types of motors in their catalog. Do a search at
the online catalog at , but pack a
lunch first.

I find the paper catalog easier to use. You should be able to
find one at any well-run maintanance facility. The rest of
the catalog is full of everything you need to build anything.

I am not associated with Grainger other than as a happy

Chunk Kiesling

Subject: RE: How Do You Cab Obsidian?

The question asked was, "How do you Cab Obsidian?" whereas
the question Mr. Beaty really wanted answered was, "Why did
my Obsidian explode?"

A possible answer to the second question is "Internal
Pressure." We have all seen tempered glass windshields go
all to pieces after being mildly scratched, and some of us
are familiar wuth "Prince Rupert Drops" which are small
(usually 1/2" to 1") with a long 'tail,' and if you break off
the tail the whole thing goes to pieces. The phenomenon in
both cases is caused by ultra-rapid cooling of a viscous
liquid, (in this case molten glass), so that a "Skin" forms
on the outside, and inside you have, rather than a solid, a
supercooled liquid under tremendous pressure. Break the
integrity of the skin, and the contents undergo explosive
decompression; but unless that integrity is broken, the
glass has tremendous shock resistance. A Prince Rupert Drop,
for instance, can be struck with a hammer, and as long as you
don't break the tail, it will not shatter.

Obsidian is made in Nature, by rapid cooling of an acidic
(high silica) magma. It is part of the series
pumice-scoria-obsidian-rhyolite, the first two members of the
series cooling so rapidly they've not had time to outgas. In
any event, exploding obsidian is rare, but not at all
impossible; if you want to make sure that it doesn't happen
again, take the obsidian you want to cut, and try to knock a
chip off it with a hammer. (Be sure to wear both gloves and
eye - protection.) If you can't chip it to a nice conchoidal
fracture, take another piece. If it comes apart in your
hands, you've saved the problem of an explosion in your saw.

As for the exact mechanics of cabbing it, all I can suggest
is practice on a piece of glass you've knocked out of an old
bottle. Obsidian is glass; in fact, it was the first glass.
(You cannot make glass without some molten glass to melt the
chemicals into.)

Hope this helps.

Ted Robles

Non-commercial republication rights granted.

Subject: RE: How Do You Cab Obsidian?

Because of the way it is formed, obsidian often has very
high internal stresses and will shatter or explode when cut.
Wear gloves, long sleeves and safety glasses.


Subject: RE: How Do You Cab Obsidian?

Many rocks have internal presures that are released when you
saw or cut them. Obsidians like Apache Tears are noted for
this. If this is the problem you can treat the stone and end
the danger. I don't have the temperature for this. The
technique is to put the obsidian in a container of sand bake
it in the oven and let it cool slowly in the oven. This will
stop the shattering. I'm sorry I don't have the exact
formula. It has been published many times.

Steve Ramsdell

Permission for non profit republishing, ok

Subject: RE: Saw Oil and PCBs

LORTONE has been selling cutting oil specifically for
lapidary for many years now. Here's my two cents worth.

NEVER, NEVER use an oil with PCB's in it. If you don't know
what it is you're using, don't even consider it.

NEVER use kerosene, diesel or jet fuel as these are FUELS
and are designed to burn! I know they've been used for years
but there's no reason to take chances when there are good

Cutting oil is designed to lubricate the cutting edge,
transfer heat from the blade and rock, and wash the cut
clean. As such, a good cutting oil needs to have the
following characteristics:

1. High Flash Point - important for cutting safety. Best if
over 300 deg F.
2. Low viscosity - Higher viscosity oils generally transfer
heat slower. Best in the 6-12 centistoke range.
3. Thermally stable - Should resist breakdown at temperature.
4. Low Additive - to minimize reactions with minerals in the
5. Low specific gravity - to help the rock fines settle out.

Transformer oils - such as the mentioned Texaco code 600 -
and many others meet these requirements very well and are
excellent for rock cutting. They have a high heat ransfer
rate, are thermally stable, and have anti-oxidants which help
prolong their life in the sump. PCB's have not been used by
the major oil companies for many years and we have never sold
oils with PCB's. Again, If you don't know what you have,
don't even think about using it.

The only problem with transformer oils (and many other
metalworking oils as well) is that they are made from
Napthenic stock which gives them the customary Lapidary Oil
"smell". In addition, it's hard on the skin as it can cause
drying and defatting.

As a result, we have switched to a pure mineral oil that does
not have the napthenic base and is therefore much less
irritating to the skin and absent of any smell. It also cuts
as well as the other oils.

Finally, breating ANY oil mist is not a good idea and may
cause a form of Lypoid Pnuemonia. ALWAYS wear a respirator
and if you are allergic or sensitive to oils consider using
plain water if your saw can handle it.

Doug Guthrie

Subject: RE: Saw Oil and PCBs

Maybe (probably) this is an ignorant question, but what would
be wrong with using vegetable oil in your saw? Isn't that
what cutters used to use?


noncommercial publish permission granted

Subject: FS: Used Tumbler and Diamond Saw

The Lapidary equipment below is in excellent working order
with all bearings and motors like new:

Lapidary Table Saw: Highland Park Manufacturing Co., Model
E-5. Water Cooled 10 inch dia. x 0.04 inch Diamond Saw with
8 diamonds per inch; container lipped cast alloy table
12 inches x 18 inches; water/oil integral reservoir beneath
table; traveling adjustable vise; automatic feed, driven via
pully gravity weight system. $160.00

Ball Mill (Tumbler): with two drums (8 inches in diameter x
8 inches tall; 7-1/2 inches in diameter x 8 inches tall); on
caster mounted platform. Manufactured by Craftool. $95.00

Available only by pickup in So. California (nr Pasadena, CA)
If interested contact< >

B. Wallace>
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