"Grape Agate", Grape-Like Chalcedony

Images taken in a controlled environment or with a posed subject. All subject types.

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Macro_Cosmos
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"Grape Agate", Grape-Like Chalcedony

Post by Macro_Cosmos »

ImageGrape Chalcedony by Macro Cosmos (DH)
Bigger version on Flickr.

Taken with the Laowa 25mm. I'd love to hear some advice on lighting, this is my current setup:

Image

Diffusion provided by some plasticy-thingy bought at Ikea. DIY diffusion box made from those metal book holders.
Image

Any advice is greatly appreciated! I find this to be harder than 1:2 and 1:1 settings, a lot harder with lower tolerances of failure. :D

soldevilla
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Post by soldevilla »

Are you sure that this is chalcedony? They look balls of fluorite.
Chalcedony is microcrystalline, never shows crystals, and quartz is not cubic.

Macro_Cosmos
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Post by Macro_Cosmos »

soldevilla wrote:Are you sure that this is chalcedony? They look balls of fluorite.
Chalcedony is microcrystalline, never shows crystals, and quartz is not cubic.
It was called grape agate initially, which some people still call it that.
Most people on sites like mindat call it chalcedony now, I am not a mineralogist expert and I just go where the popular opinion goes.

https://www.mindat.org/min-51479.html

I do not think it is fluorite though. Fluorite has a very distinct look, these are actually individual clusters not attached to any kind of matrix.

Pau
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Post by Pau »

I agree with Soldevilla, quartz can't make cubic crystals, its internal structure doesn't allow it. Fluorite is of course a a possibility, or any other transparent mineral belonging to the cubic system.
Pau

rjlittlefield
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Re: "Grape Agate", Grape-Like Chalcedony

Post by rjlittlefield »

Macro_Cosmos wrote:I'd love to hear some advice on lighting, this is my current setup:
What you have looks pretty good, but I think you could do even better with a different diffusion material.

The reason is that I can discern your holding structure by looking in through the diffuser. That implies that your subject can discern your lights, which means that your diffuser really isn't diffusing very well, which leads to overly bright specular highlights.

I suggest substituting some thin paper in place of the plastic bubble sheets.

See http://www.photomacrography.net/forum/v ... 7343#37343 and the couple of posts after that for a quick comparison of plastic bubbles and paper for effectiveness of diffusion. Postings #1 and #3 of that thread, at http://www.photomacrography.net/forum/v ... php?t=6090, show the effect of photographing the same subject with two different qualities of diffusion.

--Rik

Lou Jost
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Post by Lou Jost »

There looks to be a high ratio of glare to surface. For such subjects, besides better diffusion, I would recommend cross-polarization (with the lamp's polarizer placed on the subject side of the diffuser). And I would try a bit of illumination coming from behind and through the crystals.

soldevilla
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Post by soldevilla »

Macro_Cosmos wrote: It was called grape agate initially, which some people still call it that.
Most people on sites like mindat call it chalcedony now, I am not a mineralogist expert and I just go where the popular opinion goes.

https://www.mindat.org/min-51479.html
I know the grape agate (I do not have a sample in my collection, but it will arrive soon, I hope)

I show a fluorite "ball" that really is a group of cubes. It was collected by me (yes, this piece is in my collection).

Fluorite has a very special diffraction index, which makes it difficult to illuminate. I think I used a disposable plastic cup of coffee, as a diffuser. If you try it, take a white balance because there are plastic cups that introduce a reddish dominant.

Image

JW
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Post by JW »

This material and its nature has been extensively discussed over at mindat.org

It is quartz, although chalcedony or some other variety may not be appropriate.

Its easy enough to test, fluorite is relatively soft and quartz is much harder.
It's not what you look at that matters, it's what you see - Henry David Thoreau

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