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 Post subject: Re: Relatively low cost hand held Raman Spectrometers
PostPosted: Wed Mar 14, 2018 5:49 pm 
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dchallener wrote:
Well I *finally* have managed to port gem and mineral spectra *into* the Ahura Spectrometer. So now it is point and shoot (or put it in a bottle and shoot) and have it display the answer.

WooHoo!!


Wow! Great achievement and big move towards ease-of-use. Think that quite some people around here could make good use of it!


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 Post subject: Re: Relatively low cost hand held Raman Spectrometers
PostPosted: Sun Aug 12, 2018 1:27 pm 
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dchallener wrote:
Well I *finally* have managed to port gem and mineral spectra *into* the Ahura Spectrometer. So now it is point and shoot (or put it in a bottle and shoot) and have it display the answer.

WooHoo!!


I dont suppose you can offer any advice on how to do this? Most of the library file looks easy to produce using an Excel macro, but I am stuck on what the numbers used to represent the peaks correspod to and how to calculate them. e.g.

peaks begin
290.875122 1.686062 0.126444
510.795227 3.502348 0.344993
peaks end

The first number is obviously its position on the x-axis, and the second I suspect is the full width at half maximum, but after that im not sure.


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 Post subject: Re: Relatively low cost hand held Raman Spectrometers
PostPosted: Sun Aug 12, 2018 4:30 pm 
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I just wanted to share a particularly fun use case for this that came up last week. At the Spruce Pine gem show in North Carolina one of the dealers had a small pile of mixed Tanzania gem gravel. Just little stuff, but a nice mix of colors. I picked out a selection:
Image
I think it's fair to say that this could have been a pain to sort out using normal methods, and I know I wouldn't have bothered buying much or any. But sorting it ended up being pretty straightforward, though a couple spectra did need a little further analysis (ie, a few hessonites had peaks at higher inverse cm than usual for some reason, the zircons were variably metaminct). But it went pretty quickly:
Image
Wait, what was that last one?
Image
Image
Yup, it's a spinel, in golden-brown! I've never seen one like this before. I would have definitely written it off as a zircon or something.
(I actually scanned this one on the ride home from Spruce Pine along with a few others, which is also a lot of fun. No need to delay gratification!)

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 Post subject: Re: Relatively low cost hand held Raman Spectrometers
PostPosted: Wed Oct 10, 2018 7:17 am 
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Where can I buy one (including the software)?


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 Post subject: Re: Relatively low cost hand held Raman Spectrometers
PostPosted: Thu Oct 11, 2018 2:58 am 
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Hello. I sell them directly--you can't get PMs until you are at 10 posts, but I can shoot you an email if you wouldn't mind.

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 Post subject: Re: Relatively low cost hand held Raman Spectrometers
PostPosted: Fri Oct 12, 2018 7:57 am 
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PM is fine
knumo at hotmail.com


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 Post subject: Re: Relatively low cost hand held Raman Spectrometers
PostPosted: Mon Nov 19, 2018 8:37 pm 
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Wow! It turns out you can identify the chemistry of a garnet using a Raman. Who knew? Working on putting that into the software so I can figure out the percentage of various types of garnet present. Only supposed to be accurate within about 5%.


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 Post subject: Re: Relatively low cost hand held Raman Spectrometers
PostPosted: Mon Nov 19, 2018 10:54 pm 
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I’ve been following the updates on this, it’s certainly piqued my interest.
I don’t know a lot about Raman spectroscopy, just my good ol handheld.
What’s the cost attached to getting into something like this? How does it work (pardon my lack of knowledge)?


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 Post subject: Re: Relatively low cost hand held Raman Spectrometers
PostPosted: Mon Nov 19, 2018 11:04 pm 
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I have been experimenting with Stephen's RAMAN machine. This thing really has huge potential as both a desktop and field gem and mineral identification tool. Great progress has been made recently in areas of more convenient use. I am really enjoying experimenting and testing this tool.


Last edited by 1bwana1 on Mon Nov 19, 2018 11:25 pm, edited 1 time in total.

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 Post subject: Re: Relatively low cost hand held Raman Spectrometers
PostPosted: Mon Nov 19, 2018 11:21 pm 
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raeghan.s wrote:
I’ve been following the updates on this, it’s certainly piqued my interest.
I don’t know a lot about Raman spectroscopy, just my good ol handheld.
What’s the cost attached to getting into something like this? How does it work (pardon my lack of knowledge)?


A good lab should probably have both. Especially if you deal in rough stones because many of the other gemological tools cannot be used with rough.

The UV-Vis-NIR spectrometers are similar to your handheld diffraction, or prism spectroscope. They are useful for identifying chromophores such as copper, vanadium, iron, and chrome in stones. This is key to variety determination. For species identification you generally use pattern matching with these the same as you would with your optical one. Some of the newer digital spectrometers have databases and algorithms to assist in identification pattern matches.

The RAMAN spectrometers strong points are identification of species (no help with variety), and as Stephen has pointed out with chemical makeup as in separating the mix of species within stone such as garnet and tourmaline. It can also be indicative for location sometimes. The match algorithms often note that the closest match in the database was a sample from a specific location. This is far from determinative in my experience. The species identification is determinative. This from the latest issue of AGTA's Prisim magazines article on the state of spectroscopy in the gem industry.

"Raman spectroscopy is the only technique which can
provide for a fast, reliable and non destructive identification
of polished and rough gems, either loose or
mounted, without the need of further test (Figure 1
left). It is not by chance that a Raman spectrum is often
called “fingerprint”. Every single material has its own
and, if the spectrum is clearly readable and not noisy,
its 100% accurate. Still Raman spectroscopy provides
for very limited applications in case of synthetic gems.
Same is found with the refractometer, most of synthetic
and naturals are not distinguishable from each other. "


I hope this was helpful information.

Steve


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 Post subject: Re: Relatively low cost hand held Raman Spectrometers
PostPosted: Tue Nov 20, 2018 2:12 pm 
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dchallener wrote:
Wow! It turns out you can identify the chemistry of a garnet using a Raman. Who knew? Working on putting that into the software so I can figure out the percentage of various types of garnet present. Only supposed to be accurate within about 5%.

I have been playing around with a Master's Thesis our of U. of Arizona on this, but admit to getting bogged down. I have a very simple technique of finding peaks - I find the highest value in a region, and then use a quadratic fit to that value and the ones on the left and right, find the vertex of the parabola, and use that for the peak. Removing background doesn't seem to move the peak much if at all.
But the data in the paper seems to be doing something different. Unless I can figure it out, it won't be helpful, as they are using the actual location of peaks to determine chemistry, and their calculation of where the peaks are is apparently different from mine.
*sigh*. I suppose I can replicate their study with my peaks and calculate a different matrix than theirs, but it will take... a while... Their calculation does seem very sensitive to peak locations, too.


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 Post subject: Re: Relatively low cost hand held Raman Spectrometers
PostPosted: Tue Nov 27, 2018 6:15 pm 
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I have come to the conclusion that I cannot replicate the data in the master's thesis.
I could not replicate their peaks, and found out they were done on a Raman in the 532 range that was a little sensitive. As I result, I took the 780/785 spectra on the RRUFF database for the same garnets, and took their chemistry from the RRUFF database, and picked off the peaks from them programmatically. Then I used Excel to calculate the matrices for calcic and non-calcic garnets. The match wasn't too bad for calcic garnets. (Except for one out of 20 or so). I tried it out on the remaining calcic garnets in the RRUFF database for which the chemical information was available -- and it didn't match that well.
Unless I find an error (which is possible) I think I am going to give up on this. It would have been a nice addition to the program. Oh well.


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 Post subject: Re: Relatively low cost hand held Raman Spectrometers
PostPosted: Mon Dec 03, 2018 5:47 pm 
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Well, I have found I *can* give a pretty good estimate of the amount of magnesium present in a garnet that is calcic using a Raman Spectra. Next I have to check the non-calcic ones and see if that is also true for them.


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 Post subject: Re: Relatively low cost hand held Raman Spectrometers
PostPosted: Thu Sep 19, 2019 10:35 pm 
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Hi all; I'm new to this forum.

Sorry to revive an old thread, but I just picked up an Ahura First Defender on ebay and I'd love to know how to get spectra off of the device, as well as how to load new materials on to the device? Can you point me in the right direction? Happy to chat off-list if needed.

Thanks!
-Dan


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