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 Post subject: Elise Skalwold: Important Articles
PostPosted: Sun Dec 27, 2015 4:19 pm 
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Elise Skalwold, Accredited Senior Gemologist has been featured with two important papers currently published and now freely available on the Mineralogical Society of America website, both as a printable pdf and a reduced size pdf for onscreen viewing:

Double Trouble: Navigating Birefringence.
[pdfview]http://www.minsocam.org/msa/OpenAccess_publications/Skalwold/Double_Trouble_Navigating_Birefringence_reduced.pdf[/pdfview]

Quartz: a Bull’s Eye on Optical Activity.
[pdfview]http://www.minsocam.org/msa/OpenAccess_publications/Skalwold/Quartz_Bullseye_on_Optical_Activity_reduced.pdf[/pdfview]


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 Post subject: Re: Elise Skalwald: Important Articles
PostPosted: Sun Dec 27, 2015 10:58 pm 
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It is really great to see papers of this sort making their way into both the gemological and mineralogical literature. Wonderfully written and with high-quality illustrations, they bring esoteric subjects down to the level of us commoners in a way that is so rarely seen. For those who subscribe to Rocks & Minerals, she has also co-authored a superb paper on the various causes of blue color in minerals and gems:

"Blue Minerals: Exploring Cause and Effect."

I hope she will continue this series with other colors.

Fabulous work, Elise!

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 Post subject: Re: Elise Skalwald: Important Articles
PostPosted: Mon Dec 28, 2015 7:47 pm 
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I have just finished reading "Blue Minerals: Exploring Cause and Effect."
The article is astoundingly informative and quite a compelling read, reflecting both a reverence for science and a passion for beauty.

I really think everyone on this board would not only love this article but really benefit from the read. I certainly did.

Unfortunately, at this time, the article is not available for free download but can be purchased here:
Image
Rocks and Minerals


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 Post subject: Re: Elise Skalwold: Important Articles
PostPosted: Fri Jan 01, 2016 2:12 pm 
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I have read the articles and they both are of great interest.
Especially in the first one, the relations between birefringence, doubling images and pleochroism are thoroughly explored and well illustrated - and some old mistakes are clearly corrected.
Unfortunately my level in technical english and in optical physics make me miss some of the valuable information.
But it is good anyway to dive into these fundamentals.


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 Post subject: Re: Elise Skalwold: Important Articles
PostPosted: Fri Jan 01, 2016 2:39 pm 
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very good articles and it brought me back to our crystallography course at university,

after reading "Quartz: a Bull’s Eye on Optical Activity." i am sure Gene aka G4Lab (wish we could tag people in topics :D ) already got one or is making the quartz monochromator. its also very good to have 450 to 650 wavelengths for Refractometer,

i have studied about quartz crystal habits and the left- and right-hand forms,
Attachment:
2016-01-01_214838.png
2016-01-01_214838.png [ 46.92 KiB | Viewed 1909 times ]
(a) the trigonal pyramid's' is situated in the upper left-hand corner of the prism face 'm' beneath the positive rhombohedron 'r'. In the right-handed crystal (b) the opposite occurs

the Si04 tetrahedra are arranged helically on the three-fold axes of the space group with a right-handed helix resulting in left-handed crystals and vice versa.

this instruments internal cylinder of quartz and its polarizing filters is like a Dauphine twinning crystal which is sliced by polarized filters.

although handedness of the synthetic crystal is set by that of the seed crystal used to grow as it's been said most synthetic quartz are optically right-handed, so understanding left- and right-hand quartz is also helpful to separate natural from man made quartz or identifying those (unknown to me, probably Japanese company "TOKYO DENPA CO., LTD" ) companies are specialized in left-handed crystals,

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 Post subject: Re: Elise Skalwold: Important Articles
PostPosted: Fri Jan 01, 2016 4:45 pm 
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re: Double Trouble.
Filled with excellent info and several "I didn't know that." moments.

-I was erroneously taught that the maximum doubling of a stone was at 90º to the optic axis. Skalwold's article explains why this is misinformation and clearly illustrates that maximum doubling is actually seen at 45º. Very useful info. Max birefringence is at 90º.....birefringence is a measured feature (refractometer). Max doubling is a visual observation.

-"Taking advantage of calcite’s optical properties is not limited to artisans and scientists. Nature has also found a unique use: the eyes of many species of long extinct trilobites employed calcite prisms as corneal lenses! And it seems Nature knew the directions of zero doubling: each part of the animal’s complex eye contained a single calcite crystal with its c-axis/optic axis oriented perpendicular to the curve of the outer surface, thus eliminating any doubling of images except those viewed off-axis while also providing a large depth of field."( p.10-11.) WOW! Seriously? That's huge! A point definitely worthy of additional reading. :smt112

-I have always maintained a healthy skepticism regarding claims that Vikings used iolite and calcite as navigational tools. Is it possible? Empirically, yes. Historically? Not 100% convinced yet but getting a wee bit closer. :wink:


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 Post subject: Re: Elise Skalwold: Important Articles
PostPosted: Sat Jan 02, 2016 1:46 am 
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A very interesting article - I would have to add that this is a better written article on the subject than any other I have read - it is actually read to be understood as opposed to impress!


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 Post subject: Re: Elise Skalwold: Important Articles
PostPosted: Sat Jan 02, 2016 12:19 pm 
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Very nice papers!!! (as usual when coming from Elise!! 8) 8) )
still need to find time to read the "Double Trouble: Navigating Birefringence." i particularly enjoyed the "Quartz: a Bull’s Eye on Optical Activity." the explanation about difference between maximum doubling and max birefringence is just awesome and should be published as is in every gemological book. =D> =D> =D> =D> =D> =D> =D>
Needless to say, being an insturment nerd i found particularly COOL the part about the Quartx monochromator, definitely a must have.... :mrgreen: :mrgreen: :mrgreen: :mrgreen: :mrgreen: :mrgreen: :mrgreen: :mrgreen:
brava ELISE!!!! =D> =D> =D> =D> =D> =D> =D> =D> =D> =D> =D> =D> =D> =D> =D> =D> =D>

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 Post subject: Re: Elise Skalwold: Important Articles
PostPosted: Sat Jan 02, 2016 12:59 pm 
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very rich article described the pleochroism & polarization at very simple way, best for those who want to learn about mineral chemical composition affect on selective absorption and in other minerals Physical Optics is cause of the color also for those who are interested in cause of color this article gives useful information about how minerals or their free electron move about more absorbing wavelength of light for more energy

how cool is that colorless quartz can be used to separate any wavelength of color (quartz monochromator)

Barbra Voltaire wrote:
I was erroneously taught that the maximum doubling of a stone was at 90º to the optic axis. Skalwold's article explains why this is misinformation and clearly illustrates that maximum doubling is actually seen at 45º. Very useful info. Max birefringence is at 90º.....birefringence is a measured feature (refractometer). Max doubling is a visual observation


maybe you got confused it with pleochroism which is strongest for light traveling at 90 degrees to the optic axes


One of the interesting topics which was missing in "Blue Minerals Exploring Cause and Effect" article was photochromism and there are interesting examples like Scapolite. exposing gemstome to higher energy light part could include this topic.

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Last edited by roshanravan on Sun Jan 03, 2016 1:47 pm, edited 1 time in total.

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 Post subject: Re: Elise Skalwold: Important Articles
PostPosted: Sun Jan 03, 2016 1:34 pm 
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I suspect that there may be more articles coming.

Although the Blue article is very comprehensive, it knocks on the doors of several topics many gemologists do not fully understand.

And sidebar, picking up on Farshid's comments earlier in the thread:
Maximum birefringence at 90º to the optic axis :!:
Maximum doubling at 45º to the optic axis :!:

Maximum dichroism ? Is it really at 90º? Elise? Dick? Farshid?


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 Post subject: Re: Elise Skalwold: Important Articles
PostPosted: Sun Jan 03, 2016 2:48 pm 
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Barbra Voltaire wrote:
I suspect that there may be more articles coming.

Although the Blue article is very comprehensive, it knocks on the doors of several topics many gemologists do not fully understand.

And sidebar, picking up on Farshid's comments earlier in the thread:
Maximum birefringence at 90º to the optic axis :!:
Maximum doubling at 45º to the optic axis :!:

Maximum dichroism ? Is it really at 90º? Elise? Dick? Farshid?



somehow i have accidentally deleted that post! no worries i've edited again my previous post

the maximum birefringence is @ 45 degree (β), The optical axis in quartz corresponds to the c-axis so there is no birefringence when light passes the crystal from tip to tip. The maximum birefringence occurs when the light passes perpendicular to the optical axis, If a stone is cut with the optic axis perpendicular to the table maximum doubling will be seen only on those facet junctions observed through the stone in a direction approximately parallel to the girdle, but doubling is easily visible to within a few degrees of the optic axis.
In other word maximum doubling occurs when the exiting light travels at an angle of about 45° to the optic axis.

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 Post subject: Re: Elise Skalwold: Important Articles
PostPosted: Sun Jan 03, 2016 2:57 pm 
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Great...OK...now for maximum pleochroism...in this case, dichroism :?:


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 Post subject: Re: Elise Skalwold: Important Articles
PostPosted: Sun Jan 03, 2016 3:11 pm 
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Barbra Voltaire wrote:
Great...OK...now for maximum pleochroism...in this case, dichroism :?:

well according to "Elise A. Skalwold and Dr. Allen M. Bassett" article, Often the maximum strength of pleochroism in a colored transparent mineral occurs perpendicular to the optic axis, but The axes of strongest pleochroism may not be the same as the crystallographic axes in the monoclinic and triclinic systems.



i'd wish if Elise could participate in this discussion.

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 Post subject: Re: Elise Skalwold: Important Articles
PostPosted: Mon Jan 04, 2016 12:07 pm 
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I too was very intrigued by the monochromater. I've not seen these available but wonder if it couldn't offer an interesting means of color dialogue. Elise has a wonderful way of covering so many aspects of color in this article as well as making the science clear. I hope other colors are in the works.


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 Post subject: Re: Elise Skalwold: Important Articles
PostPosted: Wed Jan 06, 2016 7:36 pm 
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The quartz monochromator is a curiosity. It never achieved feasibility for production, because it was probably very difficult to make.
Very soon after it was invented, interference filter monochromators came about. Even though these were, and are expensive to buy, they probably cost much less than the quartz unit described.
It is interesting that it was built in Massachusetts, where the first USA technical corridor was, WAY before Silicon Valley. Anchored by MIT and all the classic USA tech companies.
If you look at the wavelength adjusting knob of the Quartz Monochromator it comes from an American Optical/Spencer microscope , circa 1950s vintage. This suggests that AO in Buffalo had a hand in building the unit. Those companies did do all sorts of OEM work, back in the day.

Here is an explanation of the technology that displaced the quartz mono. This is late model (current production) but they started appearing in the 1970s. They were what you needed for a "microscope spectrophotometer"
http://www.bmglabtech.com/en/technology ... 1-934.html

Bausch and Lomb came out with this series of instruments that functioned the same way. (ie. dial a wavelength)
http://www.bmisurplus.com/products/1310 ... 25-grating this one has a potentiometer (not a motor) mounted on it to readout to some data collection system what the wavelength is set to.
The Bausch systm had multiple accessories including light sources (tungsten and deuterium available. I think I have one of those somewhere.) and different grating and prism dispersers and a variety of accessories. It was a modular system.

When Elise told me about the article and mentioned quartz monochromators I pictured THIS:
http://www.bmisurplus.com/products/3902 ... uznach-com
Which is a dual prism, wide field monochromator. Notice the two UltraSil prisms. (Probably fused quartz and amorphous and not birefringent but these were made with quartz too.) I almost snagged one of those once but it escaped. Even though quartz is birefringent it also transmits UV very well so it was handy for building UV monos before gratings became available for free.

Here is a link to a module for the similar Bausch product and the auction has suggestions for others which show the modularity of the system.
http://www.ebay.com/itm/Bausch-Lomb-Mon ... _82wt_1147 The above auction shows an interchangeable grating module in its storage case.

http://www.ebay.com/itm/Bausch-Lomb-Mon ... 2772wt_910
It fits into one of these (above)

Which can connect like this to a lights source which were available for UV VIS or IR
http://www.ebay.com/itm/BAUSCH-LOMB-MON ... 2652wt_910

I hope we shall continue to see articles from Elise. Very nice work!


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