January 24 Through February 4—TUCSON, ARIZONA: Annual show
Welcome to the GemologyOnline.com Forum
A non-profit Forum for the exchange of gemological ideas
It is currently Thu Mar 28, 2024 12:34 pm

All times are UTC - 4 hours




Post new topic Reply to topic  [ 16 posts ]  Go to page 1, 2  Next
Author Message
 Post subject: ALEXANDRITE
PostPosted: Tue Aug 29, 2017 4:32 am 
Offline
Established Member

Joined: Tue Nov 01, 2016 6:12 am
Posts: 18
alex or not


Attachments:
1afc6d1eff8b14c2bcaf96b947db4e6a1ae4b17b.jpg
1afc6d1eff8b14c2bcaf96b947db4e6a1ae4b17b.jpg [ 41.89 KiB | Viewed 2666 times ]
8482cfb5c82907dd0d095fd7a134f27e3505c6eb.jpg
8482cfb5c82907dd0d095fd7a134f27e3505c6eb.jpg [ 60.55 KiB | Viewed 2666 times ]
9d2b766c386a072ffe0b45bcd408253dee4469b7.jpg
9d2b766c386a072ffe0b45bcd408253dee4469b7.jpg [ 47.75 KiB | Viewed 2666 times ]
Top
 Profile  
Reply with quote  
 Post subject: Re: ALEXANDRITE
PostPosted: Tue Aug 29, 2017 10:59 pm 
Offline
Moderator
User avatar

Joined: Mon Apr 02, 2012 9:31 pm
Posts: 4015
Location: North Carolina
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.

_________________
Rough and cut classic and exotic synthetic gems:https://store.turtleshoard.com


Top
 Profile  
Reply with quote  
 Post subject: Re: ALEXANDRITE
PostPosted: Wed Aug 30, 2017 2:32 am 
Offline
Established Member

Joined: Tue Nov 01, 2016 6:12 am
Posts: 18
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?


Top
 Profile  
Reply with quote  
 Post subject: Re: ALEXANDRITE
PostPosted: Wed Aug 30, 2017 3:36 am 
Offline
Gemology Online Veteran
User avatar

Joined: Mon Jun 16, 2014 1:10 pm
Posts: 850
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.

_________________
http://www.gemstore-24.com/
gemstones, precision cuts and more...


Top
 Profile  
Reply with quote  
 Post subject: Re: ALEXANDRITE
PostPosted: Wed Aug 30, 2017 5:54 am 
Offline
Established Member

Joined: Tue Nov 01, 2016 6:12 am
Posts: 18
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.


Top
 Profile  
Reply with quote  
 Post subject: Re: ALEXANDRITE
PostPosted: Wed Aug 30, 2017 1:12 pm 
Offline
Platinum Member
User avatar

Joined: Fri Feb 24, 2006 1:20 am
Posts: 2756
Location: Southern California, U.S.A.
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?

_________________
Rick Martin

www.artcutgems.com


Top
 Profile  
Reply with quote  
 Post subject: Re: ALEXANDRITE
PostPosted: Wed Aug 30, 2017 1:41 pm 
Offline
Gemology Online Veteran
User avatar

Joined: Mon Jun 16, 2014 1:10 pm
Posts: 850
Rick, I am def. not a good fotographer.

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

Attachment:
IMG_665.jpg
IMG_665.jpg [ 47.09 KiB | Viewed 2626 times ]


Fresh batteries - light is white

Attachment:
IMG_666.jpg
IMG_666.jpg [ 35.06 KiB | Viewed 2626 times ]


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..)

Attachment:
IMG_667.jpg
IMG_667.jpg [ 44.89 KiB | Viewed 2626 times ]

_________________
http://www.gemstore-24.com/
gemstones, precision cuts and more...


Top
 Profile  
Reply with quote  
 Post subject: Re: ALEXANDRITE
PostPosted: Wed Aug 30, 2017 6:46 pm 
Offline
Moderator
User avatar

Joined: Mon Apr 02, 2012 9:31 pm
Posts: 4015
Location: North Carolina
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.

_________________
Rough and cut classic and exotic synthetic gems:https://store.turtleshoard.com


Top
 Profile  
Reply with quote  
 Post subject: Re: ALEXANDRITE
PostPosted: Wed Aug 30, 2017 7:05 pm 
Offline
Platinum Member
User avatar

Joined: Fri Feb 24, 2006 1:20 am
Posts: 2756
Location: Southern California, U.S.A.
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.


Attachments:
IMG_666.jpg
IMG_666.jpg [ 54.69 KiB | Viewed 2605 times ]

_________________
Rick Martin

www.artcutgems.com
Top
 Profile  
Reply with quote  
 Post subject: Re: ALEXANDRITE
PostPosted: Thu Aug 31, 2017 5:52 am 
Offline
Gemology Online Veteran
User avatar

Joined: Mon Jun 16, 2014 1:10 pm
Posts: 850
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....

_________________
http://www.gemstore-24.com/
gemstones, precision cuts and more...


Top
 Profile  
Reply with quote  
 Post subject: Re: ALEXANDRITE
PostPosted: Thu Aug 31, 2017 6:44 pm 
Offline
Site Admin
User avatar

Joined: Sun Oct 16, 2005 12:22 pm
Posts: 21602
Location: San Francisco
To circle around, if the stone you posted MADADIDIERITE is chrysoberyl, I'd call it alexandrite.


Top
 Profile  
Reply with quote  
 Post subject: Re: ALEXANDRITE
PostPosted: Thu Aug 31, 2017 9:40 pm 
Offline
Platinum Member
User avatar

Joined: Fri Feb 24, 2006 1:20 am
Posts: 2756
Location: Southern California, U.S.A.
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?

_________________
Rick Martin

www.artcutgems.com


Top
 Profile  
Reply with quote  
 Post subject: Re: ALEXANDRITE
PostPosted: Fri Sep 01, 2017 1:03 pm 
Offline
Gemology Online Veteran

Joined: Thu Jan 03, 2008 3:48 pm
Posts: 707
Location: Vancouver, Canada
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

_________________
Allan Aoyama
http://www.omnifaceter.net <- Omnifaceter is back online!


Top
 Profile  
Reply with quote  
 Post subject: Re: ALEXANDRITE
PostPosted: Fri Sep 01, 2017 1:44 pm 
Offline
Platinum Member
User avatar

Joined: Fri Feb 24, 2006 1:20 am
Posts: 2756
Location: Southern California, U.S.A.
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.

_________________
Rick Martin

www.artcutgems.com


Top
 Profile  
Reply with quote  
 Post subject: Re: ALEXANDRITE
PostPosted: Fri Sep 01, 2017 2:37 pm 
Offline
Gemology Online Veteran

Joined: Thu Jan 03, 2008 3:48 pm
Posts: 707
Location: Vancouver, Canada
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

_________________
Allan Aoyama
http://www.omnifaceter.net <- Omnifaceter is back online!


Top
 Profile  
Reply with quote  
Display posts from previous:  Sort by  
Post new topic Reply to topic  [ 16 posts ]  Go to page 1, 2  Next

All times are UTC - 4 hours


Who is online

Users browsing this forum: No registered users and 6 guests


You cannot post new topics in this forum
You cannot reply to topics in this forum
You cannot edit your posts in this forum
You cannot delete your posts in this forum
You cannot post attachments in this forum

Search for:
Jump to:  
Powered by phpBB © 2000, 2002, 2005, 2007 phpBB Group
Gemology Style ported to phpBB3 by Christian Bullock