LAPIDARY DIGEST
Administered by Hale Sweeny (hale2@mindspring.com)
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This list digest contains the following message subjects:

1. LapDigest News for Issue No. 78 - Wed 10/29/97
2. RE: How Thick is a Cab?
3. RE: How Thick is a Cab?
4. RE: How thick is a cab?
5. TIP: Cutting Cat's Eyes and Stars
6. RE: Clamping Rocks in a Saw Vise
7. RE: Saw for Cutting a 550 lb Geode
8. WTS: Tectite


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<MSG1>

Subject: LapDigest News for Issue No. 78 - Wed 10/29/97

Received a note from Andrew Werby, with a quotation from
(sci.bio.paleontology) newsgroup describing the amount of
radiation which may be present in fossil bones and the danger
from dry-cutting such fossils; he suggests that the quotation
should be added to the information in the thread 'Dangers of
Rock Dust', and I agree. I will do so and will include an
abstract of it in the Digest when permission to use that
material has been received. The implication of it is: please
do not cut fossil bones dry, or if you do, be sure to protect
your lungs with a very good filter.

Debra Najera <DMNajera@aol.com> said, in Issue 77, that she
was cutting a cat's eye Alexandrite, and asked for advice as
to dome height. As I expected, the advice given directly
about such gem cabochons has been sparse, as this is not the
sort of stone commonly cut. I did want to call attention to
an article in Rock & Gem (11/97) about cat's eye chrysoberyl.
Think you will enjoy reading it. They also have a story about
an Arizona form with a saw which could easily cut that 550
pound geode!

It is a beautiful fall day here in North Carolina. Hope it
is also where you are. Have a good week, stay safe, and above
all, hug someone you love. Have fun....

hale
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<MSG2>

Subject: RE: How Thick is a Cab?


Hi Hale,

As I have been cutting cabs for a living the last
twenty years, the question of thickness of cabs prompts
me to comment. A large cab with a high dome can be an
inch thick or more, but some cutters produce large cabs
that are nearly flat and only 3 or 4 mm thick. It's not
really a question of the right thickness for cabs, there
are many different right thicknesses. What is important
is to cut a slab that is the right thickness for the
project in hand, with a minumum over to work with and to
avoid erring on the 'too thin' side.

If you have a chunk of fine rough you might want to
mount it on a block, as has been discussed herein, and
slice the top off, so you can see just what the rock is
like inside. Then set it on the shelf. When you have a
project you can square up the block in your saw vise and
take off whatever thickness slab you need. I keep my
expensive rough, choice lapis and super morrisonite,
sugilite, stuff like that, on blocks as described.

I think for general slabbing, a quarter of an inch is
wastefully thick although slabs cut in the early days
(when fine agate was taken out of the ground by the ton)
were often thicker than that! 1/4 inch is 6mm, after
all, and most cabs used in jewelry are only 3-4 mm.
Make sense?

Thom
lanelap@shore.net
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<MSG3>

Subject: RE: How Thick is a Cab?


This is going to be a long answer...because everything
depends on everything! Is it some precious material that
you don't want half of it ground in the grinders? Is it
jade that can be cut quite thin? Is it agate or jasper
that looks funny with a high dome? Is it a cat's-eye or
transluscent material like chrysoprase or blue chalcedony
that needs a high dome to bring out the best color? And
these are just a few of the questions that one needs to
ask himself before cutting or buying the material.

Knife makers need a certain thickness and it varies.
Jewelers need a certain height. Intarsia workers another.
Lamp shade people something else. Specimen slab
collectors another size. Cabs? I will speak in
generalities:

1) Unless you need depth, always cut thin. 1/8" to 3/16"
is fine for nearly all material. Look at great cab
cutter's finished pieces. Measure them, and note how
thick the finished cab is. Several cab (not many) will
not buy slabs from me because I usually cut at a standard
3/16". Why? Why spend that extra time on a grinding
wheel to take off an 1/8" to a 1/16" that needs to go
anyway. If it is gem material, one of the criteria is
material that will stand up to a fair amount of abuse.
Even opal and turquoise do not need to be thick (and both
are rarely available to cut thick slabs anyway). Why
waste good material...it is called a precious stone for
that reason! Study the good cab makers in your area! They
do not take jaspers and put a lopsided high dome on them
because they look hokey. And besides, they don't balance
well in a setting. Even belt buckles can stand to be thin.
I wear an agate one that is 2" by 3" and less than 3/16"
thick (it started as 3/16") unset with just a loop glued
to the back that stands up very well (someday I will set
it in silver just to enrichen it). I wear this as an
experiment.

2) If the stone is going into a ring size, rarely does it
need to be over and 1/8" thick, unless it has to have
depth for color. Slightly curved or nearly flat tops look
fine for most stones. Imagine cutting open an old Priday
nodule and finding one of the rare plumes...wouldn't you
want to get as many slabs out of it as possible? That
stuff is rare, why grind in away and only get a couple of
great stones when you could salvage it and end up with
several instead. Even large 40x30mm cabs look better when
cut thin. Why do you think diamond blade makers get
excited when they make a thin blade for us cutters. "We"
ask for them for a reason, and it is not for just opal or
turquoise. Thick of stone cutting as looking at a sphere;
a sphere can be looked at 360 degrees TIMES 360 degrees.

And this paper could go on...I'm sure others will have
opinions, and will comment further if needed.

Brewster McShaad
brewster@pacbell.net

Non commercial publication granted
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<MSG4>

Subject: RE: How thick is a cab?


--Greetings all!

IMHO, a cab is 6 mm.thick. In most slab saws this equals 6
turns of the vise adjuster. Or, once you get the first cab
cut the proper thickness, you can measure off of it.

Now remember....this is just a basic cab thickness. Good for
40x30...Belt Buckle thickness or lesser for brooches. If you
want, for example, star stones or tiger eye, it will have to
be a little thicker to allow for the chatoyancy of the
stone to play properly. Yes :) I do realize that the term...a
little thicker.. is kinda vague..but at the last few dots :>,
I went and measured the star saphires that I have and they
are 6mm finished. I would have to assume...never had the
oppertunity to work one...that it must start as an 8mm thick
slab. I mostly work with Ammonite so this isn't a problem.
but I do a lot with Moss Agtate....beautiful flowering stuff.
Yeh, I know it's magnesium oxide....but it's still pretty
stuff :)

So basically Hale, it does depend on what you are working on,
as to how thick the cab should be. OH YEA...don't forget to
mark the bezel line after you have your cab shaped! Very
important foe beginners. (Jenna, are you payin attention??)

Hope this message finds you and yours well..............Dave

Dave Daigle, Edmonton, Alberta
rokhound@planet.eon.net

The Edmonton Tumblewood Lapidary Club
http://www.geocities.com/Colosseum/Track/6574/
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<MSG5>

Subject: TIP: Cutting Cat's Eyes and Stars

How do you cut a star stone from rough and how do you get
the cat's eye or star centered.?

Star material is cut across the crystal so that the finished
cab is oriented with the top facing in the same direction as
the xl itself, cats eyes depending on the ruff can be either
in the direction of the xl, or the length of the xls, what
you are trying to do is orient the fibers inside the xl, the
star is the fibers arranged in the shape of the xl, while the
cats eye is the fibers running the length of the xl.

A good brief description of the process for cutting stars
and cats eyes is found in "Van Nostrand's Standard Catalog
of Gems" by John Sinkankas, its a handy book if you can find
it.
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<MSG6>

Subject: RE: Clamping Rocks in a Saw Vise


Hale, you said you were trying to cut a thin slice of optical
quartz. If it was a fairly small piece, I may have a
solution.

A friend of mine wanted a very thin slice to use in intarsia
and dopped his material on a facet dop. He mounted it on the
45 degree attachment used to make facet tables. Next he put
an 8-inch diamond saw blade in place of the facet lap. Using
a lot of water drip he gently nudged the material through the
saw blade to get a smooth cut. He then used the vernier to
lower the piece the several millimeters he wanted and
proceeded to make the next cut and got an even piece that was
thin and uniform.

I thought that was a neat trick and could be used to make
thin slices of material that was small enough to fit in the
faceting area. Even a 6 inch blade might work.

David Tuttle
dtt@net-magic.net
non commercial use permitted
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<MSG7>

Subject: RE: Saw for Cutting a 550 lb Geode

I recall several years ago an article in Lapidary Journal
concerning a mud-saw used to cut a piece of Alaskan Jade in
the field. They had a ready source of water power and hooked
up a water wheel affair powering the saw in a reciprocating
manner. They used a 6 foot 2-man cross-cut saw upside down,
as Dave Millis suggested, but put file marks across the flat
to carry the grit across the bolder. I remember the piece
was about 3 feet across and used a drip method to deliver the
slurry which was caught and used again. The blade was held
vertical by a couple of 2x4 posts at both ends. The saw ran
continuously for 4 weeks before it cut the boulder and used
a couple of saws. They moved the whole rig over and made
another cut so the big slab when finished was used as a table
top. Good luck!!!

David Tuttle
dtt@net-magic.net
can be used for non-commercial reprint
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<MSG8>

Subject: WTS: Tectite


Greetings All!

A friend of mine is looking to get rid of a tectite...or
meteorite. If anyone is interested, please let me know
privately.

Thank you and take care................Dave

Dave Daigle, Edmonton, Alberta
rokhound@planet.eon.net

The Edmonton Tumblewood Lapidary Club
http://www.geocities.com/Colosseum/Track/6574/
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