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LAPIDARY ARTS and FACETERS DIGEST
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Issue No. 142 - Friday June 6, 2003
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Moderated by: Thurmond Moore III
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Committed to carrying on the fine works of
Hale Sweeny and Jerry Dewbre
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POST TO EITHER LINK BELOW:
lapidary@caprock-spur.com
faceters@caprock-spur.com
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From The Moderator:

Hi all,

Another week has come and gone. I had planned
to facet some this weekend but a 70 mph wind and
rainstorm has created a bit of tree cutting for me instead
since it destroyes several 40 year old cedars and poplars.
Everyone have a great weekend no matter what you
might do. See you Monday.

Thurmond
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Index to Today's Digest

01  RE: 1st rockhound memory
02  RE: Temperature, finger pressure and polishing.
03  RE: Worst rockhound locations
04  RE: Temperature, finger pressure and polishing.
05  RE: Scratching Problem?
06  WTB:  330 epoxy glue.

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Message:01

Subject: 1st rockhound memory
Date: Fri, 6 Jun 2003 01:13:45 +0100
To: lapidary@caprock-spur.com
From: Michael Hing <faceting2@maiko.demon.co.uk>

>Jon, this brings back memories of my first rock hound trip.

My first rockhound memory is when I saw a TV programme and suddenly
realised that the curved white streaks in the limestone wall of my
school were fossilised oyster shells.

Anyone else?

?8-)
-Michael.

__________________________________________________________
Message:02

Subject: Temperature, finger pressure and polishing.
Date: Thu, 05 Jun 2003 20:38:22 -0400
To: lapidary@caprock-spur.com (LapidaryArtsDigest)
From: "Jonathan L. Rolfe" <webmaster@gearloose.com>

At 07:20 PM 6/5/2003 -0500, you wrote:
>Concerning temperature change on a lens, it said with a Foucault test,
>if you touch a spot on the polished lens with a finger, that spot will
>create an enormous "hill" (possibly 10 or 20 millionths of an inch)
>where you touched it, from the heat of your finger.
>In faceting it is said
>you should "press the stone with your finger" to the lap, not press the
>dop or quill. Is it possible the heat change from your finger (in
>relation to the stone) creates some of the problems that cause
>scratching when polishing a stone that I read about?

Probably not as significant in gemcutting as in telescope mirrors for the
following reasons:
1) We are not working to 1/8 Wave deviation to a perfect parabolic figure
when we cut gems.  A well-met meet could be off by microns..a "mile" in
visible optics.
2) Pyrex and even Cer-Vit can flow under pressure, which is why mirrors
need a certain thickness-to-diameter ratio.  Crystals tend not to as much,
discredited polishing theories notwithstading.  I notice that quite a few
gemcutters are also astronomers, for some reason!  Two lonely hobbys?
(My turn to pack for a trip now..sadly, not to CA!)


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Message:03

Subject: Re: Issue No. 141 - Thursday June 5, 2003
Date: Fri, 6 Jun 2003 01:42:36 +0100
To: LapidaryArtsDigest <lapidary@caprock-spur.com>
From: Michael Hing <faceting2@maiko.demon.co.uk>

>No,no,no!  Southeastern New England!!!  We have the dullest minerology
>there is.  Unless the winner is some desert, somewhere.  Or maybe Antarctica.

I think the winner is probably South-Eastern England.  Unless you like
clay...
?8-)
-Michael.



__________________________________________________________
Message:04

Subject: Re: Issue No. 141 - Thursday June 5, 2003
Date: Thu, 05 Jun 2003 22:55:41 -0400
To: LapidaryArtsDigest <lapidary@caprock-spur.com>
From: Kreigh Tomaszewski <Kreigh@Tomaszewski.net>

LapidaryArtsDigest wrote:
> __________________________________________________________
> Message:05
>
> Subject: Scratching Problem?
> Date: Thu, 05 Jun 2003 01:53:47 -0500
> To: faceters@caprock-spur.com
> From: gembin <gembin@spiff.net>
>
>   Hi All,
>
> Yesterday I was reading how to grind and polish telescope lenses.
> Concerning temperature change on a lens, it said with a Foucault test,
> if you touch a spot on the polished lens with a finger, that spot will
> create an enormous "hill" (possibly 10 or 20 millionths of an inch)
> where you touched it, from the heat of your finger. It also said when
> they were polishing the 200 inch telescope mirror, they used talcum
> powder on their finger to "touch up" uneven areas on the lens.
>
> My question for the experts out there is this... In faceting it is said
> you should "press the stone with your finger" to the lap, not press the
> dop or quill. Is it possible the heat change from your finger (in
> relation to the stone) creates some of the problems that cause
> scratching when polishing a stone that I read about? Could it be that
> "creating a hill" (or an uneven area on the stone's edge, etc.),
> allowing swarf, grit or oxides to "ball up" between the facet and the
> lap that could be causing scratching when polishing?
>
> Just curious,
> Doug "Rhodolite" Smith
> Alton, Illinois, USA (on the north side of the Mississippi River)
>
> __________________________________________________________

Studying the production of (telescope) optical surfaces can be daunting
to the average lapidary. Measurements used are relative to the
wavelength of light and often given in angstroms, equal to  about
0.00000000394 inch.

To put this into perspective, a particle of 120 corundum grit is
typically 0.005 inch in size, and a particle of 600 grit is typically
0.001 inch. Typical aluminum oxide prepolish runs about 0.0002 inch
particle size. Typical polish grain sizes are on the order of 0.000002
inch. BTW, if anyone has size information on diamond grits I would
appreciate receiving an update with details.

Scratch depth is typically just over the diameter of the particle that
produced it. Grinding is repeated scratching with smaller and smaller
grit sizes to prepare a surface for polishing. Starting with a rough
ground flat surface, working thru the grit sequence and pre-polish
stages typically removes less than 0.05 inch of additional surface
material.

Polishing has been shown to be more of a butter spreading effect, where
the surface is smeared, filling in the very fine scratches, but removing
some surface material too. Polishing should remove less than 0.0015 inch
of material and still eliminate all scratches from pre-polish.

What we in lapidary think of as a polished surface is only the beginning
preparations for producing a high quality optical surface required for a
telescope. Our lapidary efforts are adequate for eyeglass lenses, but
optical flats, prisms, and telescope mirrors need to be perfect to
roughly a wavelength of light. That is where the heat expansion from
touching the surface becomes important, and where a little rouge polish
(more likely than talcum powder) on a fingertip is an excellent tool for
removing a high spot using gentle pressure.

Based on my experience and readings I would suggest that the occasional
scratching encountered in lapidary work is much more likely due to
accidental contamimation with grit, dirt, or removed surface material
from an earlier stage of work. The surface rise from thermal effects is
simply too small to provide space for building a particle large enough
to make a scratch that will be visible.

If you are having problems with scratches you probably need to do a
better job of keeping your work area and equipment clean.

And if you want to do some serious practical reading on how to make
telescopes and optical surfaces you probably will not find a better
source that the three volume set "Amateur Telescope Making" edited by
Albert G Ingalls and published by Scientific American.

Kreigh

__________________________________________________________
Message:05

Subject: Re: Scratching Problem and Fingers
Date: Fri, 6 Jun 2003 18:32:30 +0200
To: lapidary@caprock-spur.com (LapidaryArtsDigest)
From: Tom Herbst <herbst@mpia-hd.mpg.de>

Doug "Rhodolite" Smith wrote:

> Concerning temperature change on a lens, it said with a Foucault test,
> if you touch a spot on the polished lens with a finger, that spot will
> create an enormous "hill" (possibly 10 or 20 millionths of an inch)
> where you touched it, from the heat of your finger. It also said when
> they were polishing the 200 inch telescope mirror, they used talcum
> powder on their finger to "touch up" uneven areas on the lens.

There are a couple of effects going on here. The first one you
mentioned is the production of a (temporary) hill, due to local heating
of the glass. When you warm up glass, it expands. Touching a lens will
heat it locally, raising a small hill that is indeed detectable in
sensitive measurements. The hill disappears when the glass returns to
ambient temperature. I have personally experienced this effect while
polishing (and Foucault testing) a six inch telescope mirror. The
second point about using talcum powder to touch up the Palomar 200 inch
mirror refers to polishing away some of the glass - in other words, a
permanent change. (I am somewhat skeptical about the use of talcum
powder to polish glass, since I presume it is very soft?) Modern
telescope mirrors are polished with both rouge (iron oxide) and cerium
oxide - what else for a huge chunk of synthetic quartz?. They are also
made of glass that has low (or zero) expansion with temperature.
Fingertips are definitely out of fashion - you are more likely to find
a computer controlled polishing lap that can actively change its form
as it moves over the glass surface.

> Is it possible the heat change from your finger (in
> relation to the stone) creates...
>  a hill" (or an uneven area on the stone's edge, etc.),
> allowing swarf, grit or oxides to "ball up" between the facet and the
> lap that could be causing scratching when polishing?

I doubt it, but the materials experts out there might want to comment.
First of all, the warmth of your finger is on the top of the stone, not
where the grinding takes place. Also, I suspect that warming by your
finger pales in comparison to temperature changes induced by the
friction of polishing or, for that matter, by the amount of cooling
water splashing around. Also, something like quartz expands about one
part in 250,000 per degree Fahrenheit. Let's say you warm the upper
millimeter of quartz by ten degrees. This will produce a hill of about
0.04 microns (or about a millionth of an inch). This is ten times
smaller than 50k diamond particles. Other effects, such as producing
"turned edges" or rounded facet meets, will certainly be a far larger
effect in "ball up" of polishing agents.

Tom Herbst
Heidelberg Germany
tom@boghome.com

__________________________________________________________
Message:06

Subject: 330 epoxy glue.
Date: Fri, 6 Jun 2003 13:02:27 -0400 (EDT)
To: faceters@caprock-spur.com
From: dojac@webtv.net (Jack Denne)

Hi all.  I live in Markham, ON. Canada. Greater Toronto area. Does
anyone there know of a supplier of the Hughes co. 330 epoxy glue?  Would
appreciate any info.
      Thanks,    Jack Denne.


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TODAY'S FUNNYS ~

INTERESTING CONVERSIONS

     You may have heard about the following new units of measure and
conversions:

Ratio of an igloo's circumference to its diameter: Eskimo Pi

2.4 statute miles of intravenous surgical tubing at Yale University
     hospital:  1 I.V. League

Speed of a tortoise breaking the sound barrier:  Mach Turtle

Time it takes to sail 220 yards at 1 nautical mile per hour:
Knot-furlong

16.5 feet in the Twilight Zone:  1 Rod Sterling

Basic unit of laryngitis:  1 hoarsepower

Time between slipping on a peel and smacking the pavement:  bananosecond

1 million microphones = 1 megaphone

2000 mockingbirds = 2 kilomockingbirds

10 cards = 1 decacards (or is it 52 cards?)

1 millionth of a fish = 1 microfiche

453.6 graham crackers = 1 pound cake

3-1/3 tridents = 1 decadent

2 monograms = 1 diagram

8 nickels = 2 paradigms

1 millionth of a mouthwash = 1 microscope

Half of a large intestine = 1 semicolon

1000 aches = 1 megahurtz

1 trillion pins = 1 terrapin

2 wharves = 1 paradox

2000 pounds of Chinese soup = Won ton



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REFLECTIONS AND TIDBITS:

Do what you can with what you have where you are.

---Theodore Roosevelt---

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