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For most of the first half of this decade, Fate put me in Germany. The city was Dortmund, a former coal and steel hub of some 700,000 souls in the industrial Ruhr valley. While it has now moved with some success to a more high-tech information and
services based economy, the blue collar coal mining and blast furnace heritage still remains strong. Here, local people have mining and smelting in their blood, and thus a feeling for things that come from below ground which is quite different from what
you'd find in, say, a farming area.
 | The cab cutting workshop at the Dortmund Museum of Natural Science, seen from the outside. |
I soon ran into mineral collectors, and through them, the Dortmund Museum of Natural Science. The director was himself a geologist, and perhaps for that reason, in combination with the city's mining heritage, the museum boasted a showy mineral collection
including one immense Arkansas quartz aggregate as big as a table top sprouting arm-long crystals in all directions, ammonites as big as automobile tires, and slabs of petrified wood the diametre of a small tractor tire. The local mineral club gathered
here monthly for presentations and specimen shows. Moreover, just at about the time I arrived, the Museum was preparing to open a demonstration cabochon cutting workshop equipped exactly as you'd find a workshop in Idar-Oberstein itself, which is, in
fact, where the equipment was acquired.
If my memory serves it was in February of 1993 that the cutting facility became fully operational, housed in a ground level octagonal annex sheltered beneath the raised entryway patio to the main museum building.
Floor to ceiling glass on four sides afforded outside passersby an unrestricted view of the cabbing machines arranged inside around the rim of the room. And you could do more than just watch. You could also take
courses there.
This was an opportunity not to be missed. Nevertheless I managed to do just that. By the time I got around to actually going to register, there was a waiting list. The courses were booked up already for a full year and a half in advance. I swallowed hard
and put my name down. Just about a year later someone else cancelled. I was in.
 | The workshop interior. This shot is taken approximately from the coarse grinding station. |
We then worked our way through medium and fine grinding to arrive finally at the polishing station near the left side of the window wall. Note how low the machines are to the ground to permit working while seated. Visitors to the Museum could drop in and
watch from the cordoned off central area.
There were six of us in the group that gathered every Thursday morning at 9 o'clock for the next ten weeks to cut our cabochons under the watchful eye of our instructor Frau Kordon. She had studied and had been hired as a fossil preparator, and had then
become attracted to stone cutting. So it was a natural that she would be the one sent to train in Idar Oberstein, learning from professional cutters there so that she could teach in turn in Dortmund. Of the learners, five of us were male, all, except for
me, retired; the other, a lady from India who taught at the local university and had sufficient professional or family connection with the stone cutting business back at home that she thought the course might be useful as well as being pleasant.
It was clear that we were learning primarily for pleasure. But Frau Cordon did not let the burden of paedagogy rest lightly upon her shoulders for all that. At the grinding machines we all had to wear white vinyl chest-to-knees aprons with the grit size
of each grinding station written in large letters upon the corresponding apron. Before you changed stations, you also changed aprons. Imperatively. Always. The very first day, as she described their proper use and care, "I will often have to scold," was
almost her first introduction. If you ventured to approach the fine grit grinding station still wearing your coarse grit apron the wrath of Frau Cordon was thundered upon you.
"Hang the coarse aprons by the coarse grinding machines, the fine by the fine. Always wash between grit stations. Don't go from one machine to the next without washing; I'll show you a special way to wash your hands. I don't like to harp on this but I
have to. I've noticed that people say "Oh, we know that," and by the fifth or sixth session they will start to go from station to station without cleaning and then I have to yell." None of this slapdash North American "let's throw it in the air and see if
it flies" approach here. Here, I quickly gathered, there was Right Way, and a Wrong Way, born partly from a different mind set and partly from generations of industrial-scale cutting practise and a vocational system in which cabochon or agate cutter is a
recognized trade designation. I smiled at the difference in style. That, at least, was not unexpected.
But there were also surprising and significant differences in substance. Here the immediately noticeable one lay in the grinding machines themselves. Thus this part of the story will focus mainly on such differences in equipment, and a future installment
will look at some of the finer differences, notably in the sequence of operations we went through to arrive at a finished cab.
Floor mounted on a stout frameworks of welded angle iron, the grinding units at the Dortmund Museum workshop had been bought second hand from production shops in Idar-Oberstein and then refurbished. They were definitely industrial machinery and not at all
transportable. Their silicon carbide wheels were fully two feet in a diameter and about 2.5 inches wide on the periphery, two wheels per unit, spaced - I'll get into the significance of this later - about three feet apart, one at each end of a centrally
driven arbor supported on ball bearings in pillow blocks. In general, the larger the wheel, the smoother the cut, and these wheels, turning at a leisurely speed of between 200 and 300 rpm under heavy gauge sheet metal splash guards cut incomparably more
smoothly than the eight inch tabletop cab maker running silicon carbide at 1250 rpm that I was used to. A water connection to keep the wheel wet and a gooseneck lamp above and
to the side of each wheel completed the unit.
It would be difficult for a hobbyist to duplicate such a system, although not impossible if you wanted to throw enough money at it. As I recall it, the wheels themselves cost in the order of 400$ at that time and you'd need at least three of them, 100
grit, 240, and 500. Nor is it the kind of thing you'd want to do in a high-rise apartment.
However, it is little trouble to adopt another significant difference in working methods, namely the "triangle of stability" working posture. This is important and fundamental enough that it is worth trying just to get the feel of it. Sit in a chair
with your knees apart. Hold a dopstick in your right hand (if you're right-handed). Now rest one elbow firmly on each knee. Lean forward. Cup your left hand, palm upward, below the right and use it as a cradle for the right hand that holds the dopstick.
Then turn the dopstick while you picture a grinding wheel there in front of you. Don't just read this, but actually do it in your chair. Can you feel how easy it is to maintain complete and accurate control of the dopstick?
"With an elbow on each knee and your hands clasped together, what you have" - so Frau Cordon explained it, "is a triangle of stability. It's almost impossible in this position to make a false move or to slip. And for a
professional working with high value material like opal for instance, one small slip can be extremely costly, cut a nick in the stone which then has to be ground out again."
Now try taking the mental comparison a step further. Imagine yourself working standing at the grinder, as many hobbyists do, with the wheels about at chest height. You get a splash of water on the floor, your foot
slips, you make a lurch. From a standing position such a lurch will almost inevitably pitch you forward, since you'll likely be leaning a little toward the wheel as you work. So you may not only damage the stone but also propel your hand right into the
wheel when you lurch. Nor do you have the easy control of the stone that you could have, for standing is always a position of more or less discomfort in which, in a sense, you are constantly fine tuning to maintain control. Compare that with the tension
free feeling when you rest your elbows on your knees as you sit.
Indeed, this was Frau Cordon's most frequent intervention as she watched us grinding: "elbows down, elbows down." It happened to all of us. You'd be intently cutting away, all attention focused on the stone, and there she'd be: "elbows down, elbows
down." I found this stance to be so much more comfortable and conducive to better results that since learning about it I try to do all my own cutting from the elbows-on-the-knees position. In my case that entailed building a bench for my grinding unit
that put the centre of the wheel at 31 inches off the floor, which is about the height of my two hands clasped together when I sit in the "triangle" position.
As far as grit sizes went the progression from coarse to fine was pretty much standard. I think the first station was equipped with a sixty grit and a 100 grit wheel. Then we went to 180 or 250 - but only, needless to say, after first hanging up our
coarse station vinyl aprons, then washing and brushing stone, dopstick, and hands including fingernails and forearms, and then putting on the 250 apron hung near that station before finally sitting down to grind on the 250 wheel. Four hundred or 500 grit
was the next wheel, depending on the stone and whether it was going to be sanded or not, for in some cases we went directly to polishing from 500 grit. All these wheels of course were the big two foot diametre type. Due to their porosity and size, they
would soak up a large amount of water if you turned the tap on before the wheel was turning. Then as soon as the wheel picked up speed centrifugal force would fling the water out in torrents all over your feet and the floor, giving Frau Cordon occasion to
scold.
Up to 500 grit, all the wheels were of the standard soft bond lapidary variety. In this type, the abrasive is held loosely, wears off quickly, and thus constantly exposes new sharp grit which makes for faster cutting
of hard materials and doesn't glaze the wheel. One of the 500 grit wheels, however, was bakelite bonded. I don't recall whether this made it harder or softer, but it did tend to build up more heat than the standard wheel, and also gave a smoother, silky,
almost pre-polish finish.
The sanding stage, where applicable, was again quite unlike anything I'd ever seen before. The wheels here consisted of two sections of beechwood logs, each somewhat larger than a one gallon paint can with a shaft running through the middle. They turned
more slowly than the grinding wheels; 400 size silicon carbide grit was applied with a paint brush. The effect, even though the grit was 400, was as if the stone had been sanded at 1000. These log sections were NEVER (said Frau Cordon) to be touched with
the fingers. Moreover they had to be kept constantly wet, otherwise they'd split. Thus at the end of the day part of the cleanup process consisted in taking the shaft with the log sections at each end (the assembly looked like a weight lifter's dumbbell)
out of the sanding station housing, and wrapping the beechwood carefully with clean wet towels.
 | Retired toolmaker Joseph Volmari at the polishing station polishing on the cork wheel. Note the stance: elbows on knees,
both hands together. |
And then finally, polishing. Again, on approximately two foot diametre wheels. Here as I recall we had the choice of wheels faced with leather, with cork, with felt (runs hot and thus is not for heat sensitive stones),
and, the most unusual one, walrus hide. Walrus leather, it was explained to us, at about one and a half inches is the thickest hide there is. Two two-foot diametre disks of such leather glued together thus yield a disk 3 inches across its working face.
That is, you're polishing on what I guess would be called the periphery of the leather, not on its interior or exterior surface the way we usually do it. Perhaps you could get a similar effect by laminating a dozen disks of cowhide together. While the
wheel itself was a bit uneven, the feel of that walrus leather against the stone was incomparably smooth. Cerium oxide was the polishing agent for most of our stones, but one wheel, I think it was the cork one, was reserved for use with chromium oxide.
 | Our instructor, Frau Cordon, at the polishing station polishing a banded agate on the walrus leather wheel. Again, note the
working position.
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A final point to come back to in this installment is that the grinding wheel spacing mentioned earlier. All stations were two-wheel stations, with the left wheel and the right wheel separated by about three feet of clear space in the middle. That meant
two persons could work comfortably at the same station. But it also meant that you never had to worry about grinding your knuckles off against the neighboring wheel when you're trying to shape the bottom edge of a stone as is often the case on hobby
machines where a series of wheels of different grits is mounted close together on the shaft.
Essentially, the professional equipment does the same job, but being larger, is significantly easier to work with. While differences like sanding on beechwood log sections are interesting, it seems to me comparatively unimportant whether you sand on these
or on rubber backed sanding cloth held on with peel-em-off cement (although, in a production setting where you're doing hundreds of cabs a day the beechwood may be much less costly). At this stage of the game, the seated and braced cutting position was
by far the biggest lesson, amounting, indeed to something of a revelation. In the next installment, a more detailed look at the steps in preparing and cutting an individual stone.
 | A selection of stones cut in the museum's workshop. |
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Copyright, 1997 by Hans Durstling
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Hans Durstling is a freelance writer, jewellery maker and stone cutter living in Moncton, New Brunswick, Canada, near the zeolite, agate and amethyst collecting areas on the Bay of Fundy. His stories, reviews and commentaries have appeared
in Canadian Geographic Magazine, The European, Toronto Globe & Mail, Canadian Mineralogist, Mineralienwelt, Rock & Gem and many others. He now works primarily in corporate & industrial writing explaining complex scientific and
technical products and processes to layman readers, and writing & narrating corporate & technical videos. A considerable portion of his time is taken up with the constant battle to keep minerals and gems ("the hobby that got out of control") from taking
over entirely.
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