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 Post subject: Raman Spectrometers
PostPosted: Mon Sep 25, 2017 8:23 am 
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I've been reading up on these and have a basic idea of what they are about now but have many
questions (no surprise there) as I can't find much info on using them for gemology.
Is there a "gemologists brief" or tutorial anywhere I may have missed?

Would one of these reduce the number of tools needed for accurate stone identification
(Is a refractometer still required for example?)
How is flourescence dealt with and so on.

I'm homing in on what I want to do with my web site but I'm looking
for a good way to do accurate work with as few tools as possible across a wide
range of gems and minerals.

Specific model suggestions would be nice. as would advice
on whether one built into a microsocope (and stereo?) would be a necessary
way to go.

Any suggestions or advice are welcome.


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 Post subject: Re: Raman Spectrometers
PostPosted: Tue Sep 26, 2017 12:58 am 
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Hi, with Raman very much depends on your budget, for identification you don't need to have microscope coupled Raman (confocal), there are couple systems dedicated to gemmology, for example, Gemmoraman-532 (http://www.gemmoraman.com). Price usually starts 10000 USD for new unite. Raman reduces a time for gem identification, but don't completely replace other tools. You will have still problems with stones problematic for Raman... for example, black spinel. Read articles at http://www.gemmoraman.com/Articles.aspx. It will give you the basic idea about Raman.


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 Post subject: Re: Raman Spectrometers
PostPosted: Wed Sep 27, 2017 6:12 am 
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Thank peters

The links were very useful.
while the prices aren't out of the question the functionality now seems to be limited
for my use judging by the info on the web pages.

If I'm understanding correctly the real benefit for these only appears
if you have large numbers of items you need to process quickly for
initial indications only.

They cannot tell artificial from natural
Coated from uncoated
Cannot identify most treatments
Some stones cannot be dealt with at all
Different types of spectrometers (multiple purchases) are needed for different tests
A supplied laptop system must be purchased as part of the deal
An experienced gemologist is still needed to interpret and confirm results with other
tools and experience at a cost that is not much more than the machine (for a year anyway).

I'm coming to the conclusion that this is a gadget that is only of use for large
batches initial sorting and not for the general gemologist - would this be correct
or am I still missing something?

It does however - suggest the robots aren't going to take over gemology any time soon!


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 Post subject: Re: Raman Spectrometers
PostPosted: Wed Sep 27, 2017 8:15 am 
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Hi, it is little more complex:
- I will say: Raman is must to have tool for everyday gemologist, there are so many applications for Raman than I could agree then it is a tool for preprocessing, in fact, is my workhorse of gem identification. 95% of all identification could be done by Raman... Yes, you need to be gemmologist and use a brain, you couldn't tell difference between many synthetics and naturals, but i will say:
- after microscope, Raman is second most important, after it:
- FTIR;
- UV-VIS;
- XRF;
-..... many others
Gemmoraman 532SG will help you in 99% of main gem identification+PL and UV transparency will be the main tool for diamonds, emeralds, spinels and corundums...

In fact, there are automatic sorting devices for diamonds, so partly robots have replaced gemmologists, but gemmology deals with so many different materials and problems then human brain is more effective tool...


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 Post subject: Re: Raman Spectrometers
PostPosted: Thu Nov 09, 2017 3:05 pm 
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Okay - I have a Raman Spectrometer that can use a fiber optic pipe to look at a gemstone that is otherwise inaccessible. I was wondering if anyone has an idea if such a thing can be made into a confocal Raman microscope?


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 Post subject: Re: Raman Spectrometers
PostPosted: Thu Nov 09, 2017 7:28 pm 
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I know how I would do it, but it would involve building the microscope from scratch. In fact, I built just such a microscope ten years ago. But now all the optics has been repurposed.

You need side access to a microscope’s optics train to insert a hot mirror between an infinity objective and its tube lens. You install the hot mirror in this space so that IR laser light coming in from the side is reflected toward the objective (and IR light coming through the objective from the target... i.e., the Raman signal... is reflected back toward the fiber optic). You mount your fiber optic on an xy translator aimed at the mirror. You’ll need to use some camera to monitor the microscope image, because there is too much invisible laser light banging around to view by eye.


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 Post subject: Re: Raman Spectrometers
PostPosted: Thu Nov 09, 2017 8:07 pm 
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Peters wrote:
Hi, it is little more complex:
- I will say: Raman is must to have tool for everyday gemologist, there are so many applications for Raman than I could agree then it is a tool for preprocessing, in fact, is my workhorse of gem identification. 95% of all identification could be done by Raman... Yes, you need to be gemmologist and use a brain, you couldn't tell difference between many synthetics and naturals, but i will say:
- after microscope, Raman is second most important, after it:
- FTIR;
- UV-VIS;
- XRF;
-..... many others
Gemmoraman 532SG will help you in 99% of main gem identification+PL and UV transparency will be the main tool for diamonds, emeralds, spinels and corundums...

In fact, there are automatic sorting devices for diamonds, so partly robots have replaced gemmologists, but gemmology deals with so many different materials and problems then human brain is more effective tool...


Agreed Peters. A trained gemologist should be able to microscopically determine and separate most things the GemmoRaman can't help you with. Positive identification of your unknown is certainly the best place to start.


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 Post subject: Re: Raman Spectrometers
PostPosted: Thu Nov 09, 2017 9:34 pm 
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I already can use the Raman for identification. The RRUFF datase was invaluable in that. But sometimes it would be nice to use the Raman to identify an inclusion, which I understand a confocal Raman microscope may be able to do. Since those cost more than I make in a year, and I have several Raman spectrometers, ....


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 Post subject: Re: Raman Spectrometers
PostPosted: Thu Nov 09, 2017 11:17 pm 
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Let's hope Nathan Renfro will weigh in.


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 Post subject: Re: Raman Spectrometers
PostPosted: Fri Nov 10, 2017 4:38 am 
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I even hope Nathan will weigh in, meanwhile i'd like to share some thoughts.
there is an actual reason why confocal MicroRamans are so complex and expensive. What Brian described above is something that can be built (he actually did it and, btw, i'd like to know more details about it! :-) ) BUT, you really need to know what you are doing AND the achievement, despite can work in some cases is far from being called a REAL confocal unit for inclusion identification. It's not a matter of focusing the optical path of the microscope and the laser beam on the same point only. a complicated synchronized system of micro-iris is necessary to focus both to the same depth.

this picture is more explicative about the concept

http://zeiss-campus.magnet.fsu.edu/arti ... igure6.jpg

the 2 pinhole apertures need to be synchronized in order to get the correct signal.
Modern confocal MicroRamans have the ability to effectively resolve distances of 3 microns... of course in gemology we do not need for such precise resolution, but anyway this is how the system works.
Besides that, what people usually miss is the fact that, even if you are able to focus the beam and get the raman signal from an inclusion, the resulting spectrum will be a combination of both inclusion and hosting material. At this point you either need to interpret the outcome by yourself (that is really something that need for a HUGE experience AND is not always possible due to overlapping of peaks) OR you need to have a sophisticated software which is able to made the job for you. All the Professional Confocal units are provided by this kind of software also and, as someone who have worked with one of them i can assure you the procedure is not "automatic" and manipulation of the data is more or less always needed.
We have been requested by many people to face the challenge of building such a unit, and we indeed took the challenge to different levels, i can assure you THAT is not an easy task to accomplish, it will need for a LOT of R&D time and the outcome will be far to be inexpensive.
that's my 2 cents only...

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 Post subject: Re: Raman Spectrometers
PostPosted: Fri Nov 10, 2017 4:05 pm 
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Alberto wrote:

...the 2 pinhole apertures need to be synchronized in order to get the correct signal.

Besides that, what people usually miss is the fact that, even if you are able to focus the beam and get the raman signal from an inclusion, the resulting spectrum will be a combination of both inclusion and hosting material.


Yes the pinholes would be more work, but possible. (I wonder if one can use just a single pinhole if you use a reflection/backscatter probe to collect the light.) And yes, learning how to separate inclusion Raman from host Raman would take a lot of time. And if you want to make more than one and have them be reliable... I can see why there is not yet a GemmoMicroRaman. :-D


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 Post subject: Re: Raman Spectrometers
PostPosted: Fri Nov 10, 2017 4:19 pm 
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Brian wrote:
. I can see why there is not yet a GemmoMicroRaman. :-D


At least not...yet!!! :wink: 8)

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 Post subject: Re: Raman Spectrometers
PostPosted: Sat Nov 11, 2017 8:17 pm 
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Alberto wrote:
I even hope Nathan will weigh in, meanwhile i'd like to share some thoughts.
there is an actual reason why confocal MicroRamans are so complex and expensive. What Brian described above is something that can be built (he actually did it and, btw, i'd like to know more details about it! :-) ) BUT, you really need to know what you are doing AND the achievement, despite can work in some cases is far from being called a REAL confocal unit for inclusion identification. It's not a matter of focusing the optical path of the microscope and the laser beam on the same point only. a complicated synchronized system of micro-iris is necessary to focus both to the same depth.

this picture is more explicative about the concept

http://zeiss-campus.magnet.fsu.edu/arti ... igure6.jpg

the 2 pinhole apertures need to be synchronized in order to get the correct signal.
Modern confocal MicroRamans have the ability to effectively resolve distances of 3 microns... of course in gemology we do not need for such precise resolution, but anyway this is how the system works.
Besides that, what people usually miss is the fact that, even if you are able to focus the beam and get the raman signal from an inclusion, the resulting spectrum will be a combination of both inclusion and hosting material. At this point you either need to interpret the outcome by yourself (that is really something that need for a HUGE experience AND is not always possible due to overlapping of peaks) OR you need to have a sophisticated software which is able to made the job for you. All the Professional Confocal units are provided by this kind of software also and, as someone who have worked with one of them i can assure you the procedure is not "automatic" and manipulation of the data is more or less always needed.
We have been requested by many people to face the challenge of building such a unit, and we indeed took the challenge to different levels, i can assure you THAT is not an easy task to accomplish, it will need for a LOT of R&D time and the outcome will be far to be inexpensive.
that's my 2 cents only...

Actually the software is pretty easy. You just have to consider the sample raman spectra to be a vector, v. Take the main stone to be a vector W, and take V-(v*w)W, and process that (where * is a dot product). This should be standard residual analysis.


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 Post subject: Re: Raman Spectrometers
PostPosted: Sat Nov 11, 2017 9:26 pm 
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Well of course, that's what I was going to say. :wink:


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 Post subject: Re: Raman Spectrometers
PostPosted: Sun Nov 12, 2017 5:32 am 
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dchallener wrote:
Actually the software is pretty easy. You just have to consider the sample raman spectra to be a vector, v. Take the main stone to be a vector W, and take V-(v*w)W, and process that (where * is a dot product). This should be standard residual analysis.


i am glad you find the thing "pretty easy". :D
have you worked on a confocal Raman software?
My experience is limited to the Thermo DXR which runs on the Omnic software. I find the feature not really easy to manage, and that is likely due to the different Raman signal strength of the hosting and inclusion. Of course its not a matter of peak position, but very often you have these 2 scatterings not easy to combine. I think, for this purpose the Onmic has a feature allowing the operator to manipulate the resulting spectrum by modifiyng its "virtual" exposure time. But the interpretation can be smetimes complicated, especially when you have a hosting material which reacts strongly while the inclusion signal is veeeery weak..... :wink:

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