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 Post subject: ALEXANDRITE
PostPosted: Tue Aug 29, 2017 4:32 am 
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alex or not


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 Post subject: Re: ALEXANDRITE
PostPosted: Tue Aug 29, 2017 10:59 pm 
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As part of getting an account set up with them I sent a chrysoberyl with a very nominal color shift in to the GIA. It was still enough to get alexandrite on the lab report. So at least some people would call it alexandrite, since the shift is much better in yours than mine. Others take a slightly more restrictive approach, where mine absolutely wouldn't qualify, but yours might.

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 Post subject: Re: ALEXANDRITE
PostPosted: Wed Aug 30, 2017 2:32 am 
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This one comes from Madagascar, weight is 2.5367 grams.
Half very clear, half milky(matbe can get cat's eye), no damage
Is there anyone know the market value of this kind of stone?


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 Post subject: Re: ALEXANDRITE
PostPosted: Wed Aug 30, 2017 3:36 am 
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Why has the background on the first pic the same color like the rough stone?

We see so many pics with alexandrite in incandescent light with a reddish background. The gem should show a change - not the whole pic.

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 Post subject: Re: ALEXANDRITE
PostPosted: Wed Aug 30, 2017 5:54 am 
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Marlow wrote:
Why has the background on the first pic the same color like the rough stone?

We see so many pics with alexandrite in incandescent light with a reddish background. The gem should show a change - not the whole pic.


THE BACKGROUND IS WHITE A4 PAPER. I TOOK THE PHOTO UNDER A BULB FLASHLIGHT.


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 Post subject: Re: ALEXANDRITE
PostPosted: Wed Aug 30, 2017 1:12 pm 
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Marlow wrote:
Why has the background on the first pic the same color like the rough stone?

We see so many pics with alexandrite in incandescent light with a reddish background. The gem should show a change - not the whole pic.

Having struggled with alexandrite photography I'm wondering how that last suggestion is accomplished. Every method I've tried, and I've tried many, results in a change in the background color. Do you have any suggestions as to lighting methods or camera settings to avoid that issue?

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 Post subject: Re: ALEXANDRITE
PostPosted: Wed Aug 30, 2017 1:41 pm 
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Rick, I am def. not a good fotographer.

But both Alexandrite pics I made with an Ipad and the lamp of my refractometer.

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Fresh batteries - light is white

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lower energie - light is a bit yellow but not the whole background.

Both stones have a strong CC

Not an alexandrite but an UE Tourmaline ( so the same problem..)

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 Post subject: Re: ALEXANDRITE
PostPosted: Wed Aug 30, 2017 6:46 pm 
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Marlow wrote:
Why has the background on the first pic the same color like the rough stone?

We see so many pics with alexandrite in incandescent light with a reddish background. The gem should show a change - not the whole pic.

This is not a fair criticism. Just look at this comparison between his picture and your second one:
Image
Your background is way redder than his. The fact that the whole background isn't affected isn't particularly relevant.
Photographing some CC gems is very difficult. A lot of the high end sellers skip it entirely and just simulate the color change with photoshop.

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 Post subject: Re: ALEXANDRITE
PostPosted: Wed Aug 30, 2017 7:05 pm 
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Stephen beat me to it. After your image is cropped, as most images are, the background is very off-color as below.

I have used exactly the same camera/lighting set-up using incandescent light in one shot and substituting 3500K daylight fluorescent in the second with no changes other than exposure if needed and I always get a reddish background with incandescent.

I think Photoshop may be the only way to accomplish identical backgrounds but there's a knee-jerk reaction among some to the effect that using PhotoShop is somehow unethical. Catch 22.

But I'm always willing to learn and if someone has a more elegant solution I'm waiting to hear it.


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 Post subject: Re: ALEXANDRITE
PostPosted: Thu Aug 31, 2017 5:52 am 
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And why is my first and third pic without a red backgroud? But you see the CC.

I wrote that in the second one the batteries had a low energie - the light becomes more yellow....

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 Post subject: Re: ALEXANDRITE
PostPosted: Thu Aug 31, 2017 6:44 pm 
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To circle around, if the stone you posted MADADIDIERITE is chrysoberyl, I'd call it alexandrite.


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 Post subject: Re: ALEXANDRITE
PostPosted: Thu Aug 31, 2017 9:40 pm 
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Marlow wrote:
And why is my first and third pic without a red backgroud? But you see the CC.

I wrote that in the second one the batteries had a low energie - the light becomes more yellow....

I see some color change, but not from greenish to reddish. I'm not clear on what kind of lighting caused the change and am frankly confused.

You say both images were made with the lamp of your refractometer, which I'm assuming is incandescent. Was the light wavelength different between the first and third image? If so, how did you manage that with the same light source?

I'm also assuming you were illustrating that incandescent images can be made without creating a reddish background. If that's correct, then what camera and settings were used to accomplish it?

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 Post subject: Re: ALEXANDRITE
PostPosted: Fri Sep 01, 2017 1:03 pm 
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To avoid the background changing colour with the different lights, you need to be able to set the camera's colour balance. It depends on what type of camera you have but all DLSRs should be able to do this.

Set up an 18% grey card under the light source before you shoot your stone. Set the white balance and exposure with the grey card, then substitute your stone in with desired background and shoot the pic with the prior settings.

Swap out your light and repeat. This should result in the backgrounds staying more or less the same colour regardless of the light source, and show the true colour change of the stone.

I'll post a couple pics of some colour-shift tourmaline I have where I did this - first under 3000k LED, then 4500K CFL.

Hope this helps

-Allan

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 Post subject: Re: ALEXANDRITE
PostPosted: Fri Sep 01, 2017 1:44 pm 
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Allan, it's been a while since I did my last color-change shots, but that's the exact method I recall using. I still got a reddish background with incandescent lighting after white-balancing.

I look forward to seeing your images. It 's entirely possible I made some error with the color temperature of my lighting. I need to take another look at that.

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 Post subject: Re: ALEXANDRITE
PostPosted: Fri Sep 01, 2017 2:37 pm 
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Since this is much more entertaining that writing up status reports, this gets posted earlier than expected. And a little shout-out to TeamView for their great remote control software :)

As per above, these photos were taken under 3000K LED and 4500K CFL lighting. You can see some differences in the background colour (it's a sheet of 96 brightness printer paper) but not huge. This may be different if you're using radically different light sources, such as candle-light.

Under 3000K LED CRI>90:
Image

Under 4500K CFL (45W photo studio bulb):
Image

I followed the process I outlined in my previous post. I shot these with a Nikon D7000, Aperture mode F10 ISO200 on a tripod with a light tent. On the camera I used the Exposure Lock function with the 18% grey card in the tent to ensure consistent exposures between light sources. Actually now that I think about it, I may have shot the LED photo with -1/3 f-stop and the CFL with no exposure adjustment. That may account for the brightness difference of the background.

Hope this helps!

-Allan

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