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1. LapDigest News for Issue No. 64 Fri 9/26/97
2. NEW: Streaking Minerals - Streak Testing!
3. NEW: Lapidary teacher needed
4. RE: Grinding Wheels
5. RE: Grinding Wheels
6. RE: Grinding Wheels
7. Re: TIP: Refurbishing Old Equipment
8. Re: Refurbishing Old Equipment
9. BIO: Andy Glenn


Subject: LapDigest News for Issue No. 64 Fri 9/26/97

We are pleased to have another article by Bill Cordua of
Univ. of Wisc..- River Falls. Bill wrote the three-part
paper on Hardness of minerals for us back a month of so
ago, and wrote the one on Luster which was published about
a month ago. Here is another one, on Streak Testing. I'm
sure you will enjoy it and will learn quite a bit from it!
Thanks, Bill!

The next issue should be published Sunday or Monday.


Subject: NEW: Streaking Minerals - Streak Testing!

Streak tests are easy tests helpful in mineral
identification. The streak is simply the color of the
powdered mineral. It doesn't matter how the mineral is
powdered - you can scrape off some with a nail or pound
the mineral to bits with a hammer. More commonly
mineralogists use a streak plate, a piece of unglazed
porcelain usually cut in a square or hexagon a few inches
across. Streak plates have a hardness of about 6.5, so if
you want to test the streak of anything harder, get out
the hammer! They can be bought from most mineral supply
houses. For example, the latest Ward's Natural Science
Establishment catalog lists them at 10 for $2.90. When they
get dirty they can be cleaned by scrubbing them off with an
old toothbrush. I often use some sand with the water to
scour off resistant streaks. If they get too dirty - heck,
toss them out - they cost less than 30 cents each. When I
was a kid, I used the back of old bathroom tiles to make
an even cheaper streak plate.

Why do a streak test instead of just looking at
the color of the bulk mineral? The color of a larger chunks
of mineral can really vary, depending on what trace element
impurities may be present. Calcite, for example, can be any
color of the rainbow ( and a few that aren't on any rainbow).
But calcite always has a white streak. So why don't the
impurities color the streak? They do, but only to a slight
extent. This is because light going through a small grain of
a mineral has less chance to interact with the impurities
than light going through a big chunk of the material.
Powdering the material thus minimizes the effect of the

Streaks are most useful in the oxides and sulfides.
Silicates and carbonates generally have white or light
colored streaks. The oxides are fun to streak. Hematite's
red streak is distinct from goethite's yellow-brown streak
and pyrolusite's coal black streak. Sphalerite is another
mineral that can be lots of colors, but gives a yellow

The streak of rocks is generally not distinctive. They
usually give a light streak that reflects their dominant
silicate or carbonate composition. If they give a red or
brown streak, it suggests the presence of iron oxides.
Of course, if the rock is coarse grained, you can try the
streak test on the individual mineral grains.

Mineral databases and texts sometimes list the
streak colors and some times don't. It depends on the
tastes of the author and the data available. All minerals
have streaks (you can powder anything if you put your mind
to it) but they may not be too distinctive (hundreds of
minerals have white streaks). I think that when a new
mineral is described, the streak should always be included.
After all, the material had to be powdered in order to do
its microprobe or x-ray analysis, so all some one needs to
do is remember to record the color. That would be a real
help to those of us who don't have well-equipped analytical
labs in our basements.

Dr. Bill Cordua

Dr. William S. Cordua Professor of Geology/Mineralogy
University of Wisconsin - River Falls
River Falls, WI 54022 715-425-3139
"Speak to the Earth and it shall teach thee" - Job 12:8

Non-commercial republish permission granted

Subject: NEW: Lapidary teacher needed

Hi all,

I have been taking jewelry classes at DeCordova Museum in
Lincoln, Mass. (just outside of Boston). There are pieces
of equipment there for lapidary work but there hasn't been
a class in years. We can get the students together for
workshops but we don't have a teacher. If there is anybody
in the area who would like to teach we can put a proposal
to the museum school.

Any takers?

Kathi Parker
(presently using pre-made cabs and prepunched bezels!)

Subject: RE: Grinding Wheels

I have an old Highland Park 8" 5 wheel machine with a flat
polisher on the end. It came with SiCarb wheels. I replaced
them after a couple of years with Galaxy Wheels from Diamond
Pacific via Bombay Bazaar. It cost me about $500 but was
well worth it. The wheels have bushings of standard sizes
that will fit just about any machine. It took me less than
2 hours to do the change out. I got an 80, 220, 360, 1200,
and 14000 wheels. Works for me.

Subject: RE: Grinding Wheels

<<Can I eventually put diamond wheels to replace the
carborundum "dinosaur" wheels and what are the advantages
and disadvantages.>>

You certainly can replace the SC wheels with diamond and
the pros far out weight the cons. The main negative to
purchasing diamond wheels is the initial cost. A pair of
SC wheels may run about $100. The same two wheels in
diamond will cost about $380 ( this includes our discount
for buying two or more! ). The pros are as follows:

....No wheel dressing - SC wheels need to be dressed flat
because they develop very annoying and damaging bumps with
use. Add $25 for a dressing tool!

....Cuts faster - Hard material will wear a SC wheel down
to the core in no time and take a long time to do the work

....Cuts cleaner - The only residue from a diamond wheel
is from the stone itself. SC wheels will develop a nasty
gray sludge that gets into everything.

....Cuts cooler using less coolant - Because you only need
to cool the diamond wheel and stone. SC wheels need more
water to cool because they do cut hotter and to flush away
not only stone waste but also SC grit from the wheel.

....Safety - Though it is rare, SC wheels have been known
to fly apart and you are less likely to cut yourself if you
slip a finger into a diamond wheel.

All these advantages adds up to a more enjoyable experience.
You get a finished gem in less time, with less cleanup,
less maintenance and a better end product because more time
was devoted to actually cutting a fine gem.

The above may sound biased but this bias is not based on
the fact that I sell diamond wheels. I sell SC wheels also.
I've personally worked with both and have the opportunity
to speak with thousands of hobbyists and pros alike and I
have not touched an SC wheel in 12 years!

Peter Erdo
Graves Company

non-commercial republish permitted
(Ed. Note: Just wanted to add three more: First, diamond
wheels are cheaper over the life of a diamond wheel. Peter
quoted prices above which showed a price ratio of 3.8:1.
If the diamond wheel lasts more than 3.8 times the life of
a SC wheel, its overall cost is less. And you can bet the
farm that it will last more than 3.8 times as long as a SC
wheel, even on cutting relatively soft materials!

With SC wheels, you start them spinning and then cut
water on - or so I was taught, to avoid having a wheel
with a water load off center and possibly vibrating and
exploding as it gets up to speed. You reverse procedure
at end, allowing some time to clear the water from the
wheel. I dislike all this fussing to start and stop, so
for me, that is another disadvantage of SC wheels.

But there are special shapes which may be most easily
formed on a SC wheel; beads, for example. You form a
groove in the SC wheel and use that to shape the beads.
The procedure will be described in LapDigest a little
later, when we focus on bead making. hale)

Subject: RE: Grinding Wheels

Hi Hale, et al...regarding silicon wheels vs.. diamond:
Currently I have six Poly arbors set up with 8" diamond
wheels of various types & grits, with the exception of one
wheel that is a 60 grit 6" x 3" (that's right,three inches
wide - special from Crystalite - cuts like crazy!!). One
of these days I will find another Poly arbor (used to be
manufactured in Pasadena/Monrovia, CA) as they were the
best to ever bless the art of lapidary for general work
that most of us do. And when I do, I will put a couple of
those old dinosaur carborundum wheels on it!!!

Carborundum wheels have only two major disadvantages. The
worst is that they go out of round (bump) too quickly
except for the hard wheels (which are good for only one
thing-sharpening metal!) and therefore require too much time
in dressing the wheel. This is not much of a problem if a
person carves a lot or does only minor amounts of cabbing.
Otherwise, this is a Major drawback.

The other problem is that the wheels wear down, and
therefore the cutting speed slows down (surface speed)
likewise. This too is not a problem, especially if a person
does a lot of carving (sometimes an advantage over a large
diameter wheel) or only minor amounts of cabbing. But in
both disadvantages, this is primarily a problem with the
220 wheel and not so much for the 100 wheel.

Now, you may wonder why, with such a huge investment in
diamond wheels, would I be looking for another arbor so
that I can set up a "dinosaur"? Simply put; because they
cut so nice! Especially on softer stones like opal,
turquoise, and such. Also, they are nice to flatten the
backside of cabs. As for cutting so slow, there is not
that much difference between the two mediums, and if the
"artist" is also a silversmith, there is the advantage of
using the wheels for metal. For sphere making, most of the
old timers still making spheres will use nothing else but
carborundum to do their preforms.

It's been many years since I switched to diamond, but one
thing that comes to mind is that after the first few hard
rocks, I was disappointed that the wheels didn't cut as
fast as all of the diamond makers were touting. But, they
didn't bump, wear down in size, contaminate other wheels,
or fill the splash pans. And diamond cuts consistently the
same, day after day, week after week. I also use diamond
belts on expando drums, although I got a lot of great
polishes off of old worn-out carborundum belts. But I
don't miss the old belts flying apart when you least
expect them to do so, though. And I used to hate the kind
you would have to "thread & lock". I gave those away.

I also don't miss the way S.C. grinds skin and nails so
quickly. I used to bleed a lot and always have odd looking
fingernails (I only dop stones in the later stages of
sanding, preferring to preform most cabs by hand). One nice
thing about S.C. is when you are making odd shapes like
hearts, crosses, free forms, grinding fire agates and such.
Also, the side of a S.C. wheel for the backs of cabs is far
superior than a diamond wheel and eliminates the need for a
diamond disc.

If you have all of your wheels on one shaft, then diamond
is the only way to go, as you may only have to puts wheels
on once in a lifetime. If you have the room and plenty of
arbors, then I would recommend keeping a couple of S.C.
wheels handy, as they do have a purpose/use. Especially
if you can find or get a good deal on 10 or 12 inch wheels.

Personally, if all I ever did was to cut cabs, I would use
just one arbor and have it set up with S.C. Unless, of
course, if I was doing commercial cutting or nothing but
very large cabs, then diamond would be the only choice.
Also, if I was doing much intarsia, I would have a S.C.
wheel or two around. Someday I may be able to afford to
have Crystalite custom make me some wheels that could cut
on the sides as well as the peripheral, but meanwhile, I
will continue to look for another Poly arbor and will buy
a couple of 12" S.C. wheels when I find the arbor


Subject: Re: TIP: Refurbishing Old Equipment

In writing about rust removal both Jeff <>
and Derek <> were using mechanical
methods of rust (corrosion) removal.

There is a chemical on the market that I have used often
with great results, after the mechanical methods, Naval
Jelly, available at almost any hardware or *-Mart (add
your favorite K or Wal) is a phosphoric acid treatment.
Just follow the precautions in the instructions, and I
would recommend using this stuff outside only. Then use
the paint.

Earl English

non-commercial republish permission granted

Subject: Re: Refurbishing Old Equipment

Now that we have given a little of the directions for
taking the machine apart, let me pose a question. How do
you loosen that last nut, bolt, or screw that is rusted
into position. I have been using transmission fluid to get
things loose. I let it soak overnight. Sometimes it
works very well, others no luck. Anyone have a better
way? (without buying half a hardware store)

Steve Ramsdell

Republish for non profit permission granted
(Ed. Note: Steve, I use penetrating oil. Still have an old
can, but haven't seen it on the store shelves for years.
But really haven't looked for it! It is very thin, works
beautifully and slips into tight places nicely. I think
Liquid Wrench is a branded version. hale)

Subject: BIO Andy Glenn

My name is Andy Glenn. I live on Johns Island, South
Carolina which is about 10 miles west of Charleston, SC.
I have been interested in gems and the lapidary field for
over twenty years. I have MS and retired from teaching
about six years ago. Needing something to occupy my time,
my wife, Joyce, and I decided to start a gemcutting

Being restricted to a wheelchair and the fact that my
field of study was physics, I became interested in the
technical aspect of faceting and cabbing. I have acted
as a consultant for Fac-ette Manufacturing testing new
ideas and designing a few of my own.

In the past couple of years my wife and I have traveled to
many different areas to see and learn as much as we could
about gems and cutting. We have been to Arkansas several
times looking for diamonds. Joyce actually found one on a
trip in 1996. We have visited the Woodward Ranch several
times and visited the copper mines in Arizona collecting
azurite and malachite.

My wife and I facet on a GemMasterII and we have a couple
of cabbing machines. I enjoy helping people with faceting
or cabbing problems and communicating over the internet.
My wife has recently become interested in intarsia. I have
started trying to incorporate some of our cabbing material
into making knife handles.

My e-mail address is:

Andy Glenn
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