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dmillard
Joined: 24 Oct 2006
Posts: 456
Location: Austin, Texas
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 Posted: Thu Jan 01, 2009 7:05 pm Post subject: Fire agate |
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Approx. 5mm field width, 35mm Canon Macrophoto lens,, stacked in HF
I just photographed a piece of fire agate that I've had for the last 30 years. The iridescence is caused by interference colors from the thin layers of iron oxides deposited with the quartz during the formation of the stone. The surface of this piece was a little scratched, so I cut the end off of a glass shell vial to use as an immersion chamber, and submerged the stone below some oil of anise, which has a refractive index of about 1.5, close to that of quartz.
This image was therefore taken through both the oil and the clear quartz surface to record the interior colors. |
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augusthouse
Joined: 16 Sep 2006
Posts: 1197
Location: New South Wales Australia
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| Posted: Thu Jan 01, 2009 7:23 pm Post subject: |
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David,
Interesting subject and approach.
How 'thick' was the agate and how deep (approx.) was the oil of anise.
David wrote:
| Quote: | | This image was therefore taken through both the oil and the clear quartz surface to record the interior colors. |
This has me particularly interested.
I've heard of a similar approach being used with amber and immersion oil and I would like to lock the technique into memory for future recall.
The explanation regarding the iridescence is also fascinating.
Craig
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To use a classic quote from 'Antz' - "I almost know exactly what I'm doing!" |
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Charles Krebs
Joined: 01 Aug 2006
Posts: 4072
Location: Issaquah, WA USA
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| Posted: Fri Jan 02, 2009 12:02 am Post subject: |
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David,
Gorgeous.... just a beautiful picture! Great image to start 2009!
Craig... in the "old" forums (search for "amber") are a few shots I did exactly three years ago using immersion oil and a cover slip to "improve" the imperfect surface for photography. Made a huge difference.
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augusthouse
Joined: 16 Sep 2006
Posts: 1197
Location: New South Wales Australia
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| Posted: Fri Jan 02, 2009 12:16 am Post subject: |
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Thanks Charlie,
It just so happens, that it was to your posts I was referring to regarding "amber and immersion oil". 
Craig
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To use a classic quote from 'Antz' - "I almost know exactly what I'm doing!" |
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rjlittlefield
Site Admin
Joined: 01 Aug 2006
Posts: 12572
Location: Richland, Washington State, USA
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| Posted: Fri Jan 02, 2009 12:34 am Post subject: |
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David, this is lovely indeed! Can you explain a bit more about the big "cells" in the picture? Is each of those cells a single crystal of quartz?
Craig, about the oil, I used a similar concept HERE, for photographing the inner workings of an LED after sanding its surfaces more-or-less smooth. My oil job was, um, a bit less sophisticated, however. 
--Rik |
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Aynia
Joined: 01 May 2008
Posts: 724
Location: Europe somewhere
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| Posted: Fri Jan 02, 2009 2:38 am Post subject: |
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| Very lovely. |
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Cyclops
Joined: 05 Aug 2006
Posts: 2718
Location: North East of England
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| Posted: Fri Jan 02, 2009 4:06 am Post subject: |
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Not sure what fire agate is but its a great shot!
Rik I just checked out that flashing LED shot of yours in that link,very cool!
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Canon 30D | EOS Rebel 2000-film(aka EOS 300) | Panasonic FZ-7 EB | Vivitar/Cosina 100mm f3.5 macro lens | EF 75-300 f4.5-5.6 USM III | EF 50 f1.8 II | Vivitar Series 1 19-35 f3.5-4.5 | Slik 88 Tripod. | My new blog:
http://mybackyardsafari.blogspot.com/ |
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dmillard
Joined: 24 Oct 2006
Posts: 456
Location: Austin, Texas
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| Posted: Fri Jan 02, 2009 6:54 am Post subject: |
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| augusthouse wrote: | David,
Interesting subject and approach.
How 'thick' was the agate and how deep (approx.) was the oil of anise.
I've heard of a similar approach being used with amber and immersion oil and I would like to lock the technique into memory for future recall.
Craig |
Thanks Craig -
The piece of fire agate sat in a chamber about 10mm high and 20mm in diameter, covered with about 1-2mm of oil, varying in depth because of the irregular convex shape of the stone. There is only a thin layer of clear quartz over the hills of opaque reflective iron oxide, since the goal of the lapidary is to remove as much of this layer as possible without cutting through the "fire". I used a glass cell to contain the stone and oil because I was unsure whether the oil would dissolve plastic (a consideration also if you are working with amber or copal resin).
I worked as a bench jeweller for about 10 years (a long time ago), and also cut many faceted gemstones during that time. Immersing the rough material in liquids having a similar refractive index permits you to see the internal inclusions and fractures, and make better choices when you cut the stone. The more closely you can match the refractive index of the liquid to that of the stone, the greater the transparency you can achieve (like an ice cube in water). I liked to use oil of anise, because the high refractive index (1.55) is close to that of quartz, it is readily available (you can now find it at many grocery stores like Whole Foods, because of its use in aromatherapy), and because it makes the house smell like a candy store. The refractive indices of many essential oils can be found on the Internet. It is imperative that you use essential oils, and not the flavorings diluted with alcohol.
You may be interested in looking at The Internal World of Gemstones, by Edward Gubelin. It has some wonderful images. It was published in 1974, and sells for high prices used, but may be available through a library.
| Charles Krebs wrote: |
David,
Gorgeous.... just a beautiful picture! Great image to start 2009! |
Thanks Charlie,
Your amber insects are superb! I also like the idea of using a cover glass when possible, instead of an open immersion cell, to reduce the degree of evaporation of the volatile oil, to eliminate a reflective meniscus, and to protect the front element of the lens from potential contamination.
| rjlittlefield wrote: |
David, this is lovely indeed! Can you explain a bit more about the big "cells" in the picture? Is each of those cells a single crystal of quartz? |
Thanks Rik,
I liked the flashing LED! The cells are the mounds of the underlying iron oxide goethite (named after Goethe, who was an ardent mineralogist in addition to his other accomplishments) which frequently has a botyroidal, or globular, habit. Malachite (a copper carbonate) and hematite (another iron oxide) also often exhibit this form. |
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