[meteorite-list] Amgala vs. Zag

From: John K. Gwilliam <jkg_at_meteoritecentral.com>
Date: Thu Apr 22 10:31:14 2004
Message-ID: <6.0.3.0.2.20040416082742.0262d960_at_mail.theriver.com>

Good Morning All,
Bernd's second paragraph brings up another issue we all have to deal with,
the color temperature of the lighting we use when taking pictures of
specimens. The most accurate light to use is natural sunlight with light
cloud cover. The clouds are needed to reflect the white light onto your
subject while at the same time blocking the blue from the sky. If you are
taking pictures on a cloudless day, build yourself a light tent ( a
diffuser)out of very thin, translucent white cloth or paper. This
eliminates the blue color and give you a perfect white reflection on not
only stone meteorites, but on polished iron specimens as well.

Fluorescent lights will add a green tint to you pictures, and incandescent
bulbs (like standard household bulbs) turn everything yellow/orange.

If I must take pictures indoors, which is often the case, I use
professional lighting in the 3,200 Kelvin temperature range. This way, the
color of my specimens are as consistent as possible. Here is a simple
chart of the color temperature of various light sources.

Candle - 1,900 K
60-watt Household bulb - 2,800 K
Professional lamp - 3,200 K
Fluorescent light - 3,700*
Sunrise and sunset - 2,000 to 3,500 K
Cloudless midday sun - 5,600 K
Hazy day - 8,000 K

* Fluorescent light color temperature varies according to the age of the
lamp, coating, filtering and other factors.

If you're using a digital camera that has a white balance feature, learn
how to use it and your pictures will come out more color correct. If
you're using a 35mm camera with indoor lighting, use tungsten balanced film
to get rid of the yellow/orange tint.

With a good photo editing program, you can alter the colors of images in
your computer to make them match the original specimen pretty
closely. Remember though, all computer monitors don't show your images the
same as your monitor. A good practice is to include a photo color card and
a true white card in some test pictures. Then when it comes time to edit
the picture(s) you simply correct the color in the image to match the color
cards sitting on your desk. Use the same correction values to correct the
color in you pictures without the test cards showing and you have a
finished product that looks like the original object.


Have a great weekend,

John Gwilliam



At 07:18 AM 4/16/2004, bernd.pauli_at_paulinet.de wrote:
>Hello John D., Jeff K., and All,
>
>I agree with Jeff's remarks that the crust on Amgalas looks more
>"velvet-like".
>My cut Amgala slice (8.5 grams) which I got from the Hupes has brownish
>subangular clasts and dark, chondrule-rich material into which the light-brown
>clasts seem to be embedded. The dark matrix areas are more dominant and
>broader in my Amgala slice whereas they look more delicate and vein-like in
>my Zag pieces. The overall texture of the matrix is coarser in my Amgala than
>in my Zags and my Zags also have a bluish or grayish hue and, moreover, no
>light-brown clasts.
>
>I am attaching two JPEGs of the two pieces I am comparing with my private mail
>to John D. AMGZAG-01 was taken in daylight but not in the sun. AMGZAG-02
>was taken in the afternoon sun.
>
>Best wishes,
>
>Bernd
>
>
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Received on Fri 16 Apr 2004 11:50:39 AM PDT