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Techniques for Collectorshand spectroscope question

5th Mar 2013 16:45 UTCJako Schonken

Hello

While in a secondhand shop yesterday, I stumbled upon a "Kruss Hand Spektroskop" and consequently bought it as it was so cheap, well built and I knew it had something to do with gemology.

I do not collect gems, so my question is this; can I use it on crystals (eg emeralds) as well? Or does the stone have to be polished and reflect light in a certain way? Also, this particular model, the Kruss 1504, has a wavelength scale. Is this only used to measure the areas of absorbed light? Has birefringence or RI values got anything to do with hand spectroscopy?

Any information and tips will be much appreciated as I am still learning to use this device.

Thanks!

Jako

5th Mar 2013 16:47 UTCJako Schonken

-- moved topic --

5th Mar 2013 17:35 UTCMarc Maes

Yes, you can use it on crystals.

With the scale you can read the exact wavelength of the absorption features (lines, bands).

No, birefringence or RI values have nothing to do with the spectroscoop.

5th Mar 2013 17:44 UTCOwen Lewis

Hi!

Lucky you. Kruess use to make some lovely gemmological instruments. What you have is a spectroscope of the Amici prism design. This has both advantages and disadvantages, The scale you see will be marked off something like 400 - 700 on a non-linear scaling. These, in nanometres, are the wavelengths of visible light, Red at about 700nm and violet at about 400nm. The spectrum colour of light varies with the wavelength between these extremes of the visible electromagnetic spectrum.

What you use it for is to see parts of the spectrum where light of some wavelengths has been absorbed by being transmitted through some transparent substance, the absorption resulting being a characteristic of the material that caused the absorption. This is very useful in the identification of *some* minerals that will transmit light.The wavelengths of absorbed light show up as dark lines or bands in the observed spectrum, the wavelength or bandwidth of which can be read off the scale. Your instrument may or may not have lost its calibration.

A first check that will let you see something interesting and to focus the spectrum image properly, is to point your 'scope at a white flat panel LCD screen. If the unit is workling properly, you should see a full colour spectrum with quite a few lines visible, these being the wavelengths that the screen pixels either do not emit well or even emit at all.

Out of over 400 gem varieties, including synthetics, there are only about 95 that generally show an identifying spectrum (probably most synthetics show one. Of natural stones only a relatively few show patterns of absorption that are reliably diagnostic. These are the ones to learn with first. The rest that offer up an absorption pattern need that interpreted through experience and much practice, beginning with a set of reliable pictures of what you should be looking for.

In addition to a properly functioning scope, you need a good,strong, artificial light source to generate a full spectrum, strong and true, to pass through your test subjects. A halogen source with a collimated output via a fibre optic is probably the best general lighting solution but not only one. The best new students guide to gemmological spectroscopy in the English language, bar none. is written and published by Colin Winters. See http://www.oplspectra.com/index.php?option=com_virtuemart&page=shop.browse&category_id=1&Itemid=31

Good luck!

Owen

P.S if you decide to sell it I'd always be interested to hear from you:-) Not that I need another but it's a nice piece to have that Kruess ....

5th Mar 2013 18:00 UTCSpencer Ivan Mather

As a gemmologist I can say that the best way of doing this is to mount your spectroscope on a stand, with the eye-piece placed upwards at 45 degrees, then take a strong white light and place it opposite and level with the other end of the spectroscope, leaving a space of about one inch between them, this will now form a topside down triangle, and at it's apex place the mineral to be tested, when looking through the spectroscope you will see a full spectrum plus dark lines and bands, it is these dark lines and bands that tell you what other elements are in the specimen, other than what you would expect.

Spencer.

5th Mar 2013 18:30 UTCJako Schonken

Thanks for the quick feedback!

Owen imagine my surprise when I saw the price of a new one! I actually feel quite bad for the guy who sold it to me, he thought it was something to do with a Bunsen burner and didn't have much value. Luckily it got saved from a potential fiery death! :-D

I read that it is possible to re calibrate it by rubbing household salt in a candle wick and calibrating it according to the absorbed spectrum. Will that suffice or do I have to take it to a gemologist? I have to say, when I look at an emerald specimen from Zambia, it shows the right absorption pattern.

Another thing; when I adjust the external mirror shown here in the red circle so that light passes through the hole (red arrow), it shows another spectrum underneath the existing one. What is its function as it looks different than the top one?

I will be building a proper stand for it with a light source and a swivel so I can analyse reflected light off a mineral as well. If I finally decide to buy a proper microscope, will I be able to see the spectrum of smaller grains accurately if I fit the spectroscope to the eyepiece?

I will be having a look at that book Owen, do you know of any PDF documents I can download in the meantime that show the visible spectrum of some minerals?

Thanks for the help! And Owen you will be the first to know if I decide to sell it :)-D

Jako

5th Mar 2013 19:36 UTCOwen Lewis

You raise some some interesting points:-)

- If you already know and can find and identify the differentiatiing specrum of a Zambian emerald, then you are not quite the novice I took you for :)-D.

- AIUI, the second spectrum is to let you compare spectra from from your light source direct with the spectra from your specimen. Somewhere I've an out of print book on older gemmological instrumentation and will come back to you if that advises differently.

- Be advised that hand spectroscopes are best used to collect and examine light that has been transmitted through rather then reflected off specimen. The longer the transmission path of the light through the crystal the more definite and detailed the resulting spectrum is likely to be.

- I'd leave building a stand for a while. The great advantage of the hand spectroscope is its small size and portability. Experts learn to use one hand held and using a pen torch that has a Xenon bulb of similar as the light source. These will go anywhere with you. Remember that optical spectroscopy is best in low/nil ambient light conditions. Watch out for your fingers! Your nails have a spectrum of their own.

- Yes, a hand held spectroscope can be fitted in the ocular tube of microscope but there are few who manage to make this work well for them. My attempts at it were disheartening ; however, I recently acquired a Xenon arc lamp and that may give me the inspiration to try again:-)

- Salt and candles. This is an attempt to produce the special light that comes from Sodium atoms that is yellow and with two diagnostic lines that are close together the small separation of which is known exactly. A better way is to heat a large NaCl crystal (grow one!) in a gas flame and use the yellow glare emittedby it as your sodium light source. Less fuss to use the absorption lines in sunlight (hence the fact that sunlight cannot be used as your standard light source). There are net resources aplenty that will explain these Fraunhofer lines and list their wavelengths for you.

5th Mar 2013 19:36 UTCDavid Von Bargen Manager

Salt in a flame should get you the emission spectrum for sodium. There is a strong yellow doublet at about 589nm (you can compare that to the scale in the instrument.

http://physics.nist.gov/PhysRefData/Handbook/Tables/sodiumtable2.htm

http://en.wikipedia.org/wiki/File:Na-D-sodium_D-lines-589nm.jpg

6th Mar 2013 12:09 UTCOwen Lewis

Jako,

I read up the very little there is on the Kruess 1501/1504 in Peter Read's 'Gemmological Instruments' last night. It refers only to the 1504 having an arrangement to introduce light from an external source for the purpose of illuminating the scale. Details of that special light source and its positioning can be seen in the illustrations here http://www.kruess.de/shop/Spectroscopes:::10.html. You can see too that current production is without the external mirror and arm fitted to your older piece. If you can't work it out, an enquiry of Kruess should give you an authoritative answer. Looking at that KL14-1504 rig, I swear I was salivating :-)

Your comment re. Bunsen (yes he of the burner) being mentioned by the seller is interesting. Bunsen worked with Kirchoff in the mid-19th C on certain variations in spectroscope design that led towards the design of the 1501 and 1504 units from Kruess.

6th Mar 2013 16:35 UTCJako Schonken

Hi everyone

After successfully calibrating the scale on the spectroscope with some broken salt crystals from Cape Cross, Namibia (man, does it give off a bright orange spectrum!), I am playing around with some light sources. I find that CREE LED's work best as they are super bright and emit white light.

Speaking of light, why is it better to have a fiber optic light than a direct light source? Light dispersal and ease of use?

I also found that the mysterious ampules/test tubes that was in the box (visible in the second pic) fit through a hole in the spectroscope. I suppose it is to test liquids like blood or other organics like dyes?

I read up quite a lot on the subject of spectroscopes last night and it is interesting what you can do once your eyes get used to the small changes of light and you have enough experience! Especially to pick up REEs in gems since I am an avid collector of all the rare and ugly minerals!

Owen it is strange that there is so little written on the model, I found bits of info as well but nothing substantial. I would really like to know when my model was made. I know exactly why Kreuss stopped making the mirror attachment, it is near impossible to get light from one sample to all three openings at once!

I'm having so much fun reading up on all the gemological instruments that I might just start collecting gems! :-D

Thanks for all the feedback and tips!

6th Mar 2013 21:00 UTCOwen Lewis

Jako,

Jako Schonken Wrote:

-------------------------------------------------------

> Hi everyone

>

> After successfully calibrating the scale on the

> spectroscope with some broken salt crystals from

> Cape Cross, Namibia (man, does it give off a

> bright orange spectrum!),

First problem. Sodium light is bright *yellow*. Two bright lines separated by 0.6nm only. Unless your eyes and spectrosope are particularly fine, you are likely to see them as one fatter line with no separation. If you are seeing *orange* light something is wrong. as that can't be produced by pure sodium and is therefore useless for calibration. Get a Fraunhofer line chart and see if you can identify a couple of the stronger lines when you use the sun as your light source. Use these for calibration (use two, well spaced apart, and you are less likely to make a mistake). Before doing this, make sure that the slit is closed to an absolute minimum.

> I am playing around with

> some light sources. I find that CREE LED's work

> best as they are super bright and emit white

> light.

>

> Speaking of light, why is it better to have a

> fiber optic light than a direct light source?

> Light dispersal and ease of use?

Using a traditional incandescent light source, as much if not more energy is concentrated on your gemstone in the IR band (as heat) than is in the vis band. This is undestrable and (reputedly) can cause a stone with incipient cleavage or a major fracture to come apart. if exposure is prolonged, One way to reduce the heat reaching the specimens, is to use a goose-necked 'cold light' fibre optic feed. This also is a very valuable auxillary light source for use in microscopy and refractometry. LEDs may have bright white light now but are not known for the uniformity of their output right across the spectrum. Ask the manufacturer for a graph of something llke lumens against wavelength from 400 to 700nm. If there are any major dips or - even worse, notches, then however useful for other things, avoid using one such for spectroscopy. The very best lights are quite expensive - so you pay for perfection. Tungsten halogen bulbs are not the best but they are cheap and are what most people use: they are good enough. Whatever, don't use any light source for for spectroscopy until you *know* its output is notch-free.

> I also found that the mysterious ampules/test

> tubes that was in the box (visible in the second

> pic) fit through a hole in the spectroscope. I

> suppose it is to test liquids like blood or other

> organics like dyes?

I think not. I'm guessing but I think these have to be a way of filtering the light so you only see one colour (part) of the spectrum. This technique can make it easier to spot weak lines, especially at the blue end of the spectrum. CuSO4 solution has been used traditionally as a blue filter of known and useful properties. Again, don't try and use other solutions until you have read in thoroughly and are sure that their effect is entirely understood and predictable.

> I read up quite a lot on the subject of

> spectroscopes last night and it is interesting

> what you can do once your eyes get used to the

> small changes of light and you have enough

> experience! Especially to pick up REEs in gems

> since I am an avid collector of all the rare and

> ugly minerals!

>

> Owen it is strange that there is so little written

> on the model, I found bits of info as well but

> nothing substantial. I would really like to know

> when my model was made. I know exactly why Kreuss

> stopped making the mirror attachment, it is near

> impossible to get light from one sample to all

> three openings at once!

If you contact Kruess ar the URL given, I'm sure they will be happy to answer your questions.

> I'm having so much fun reading up on all the

> gemological instruments that I might just start

> collecting gems! :-D

I know very expert gemmologists who swear by their spectroscope and reach for it before anything else other then a loupe. That's not me. I use mine in a support role only, rather than in a primary role. Spectrometry, be it UV-vis-NIR, FTIR or Raman, is a different kettle of fish altogether - but so is the capital outlay - and none of these are 'plug 'n play' toys :-D

> Thanks for all the feedback and tips!

Ne nada.... But watch that calibration!

8th Mar 2013 16:56 UTCcascaillou

Some advice for beginers:

As a beginner, diffraction grating spectroscope is easier to start with than prism (the OPL pocket model is nice). But with some experience, prism spectroscope with graduated scale is best (although less portable). Of course the spectrum of a given stone will be exactly the same in both types.

Spectroscope can be used on any transparent to transluscent stone (cut, polished or rough, colored or colorless). Although many stones do not show any spectrum to be observed.

What a spectroscope is good for:

mostly for identification (some stones have a characteristic spectrum), and separating natural from a synthetic (some synthetics do not show the same spectrum than their natural counterpart)

Introduction:

Start by looking at incandescent light from an halogen bulb: not any absorption or emission to be seen (if any lines are seen that means your spectroscope has some dirt in it and needs to be cleaned). By the way, take great care of your spectroscope: avoid dust or humidity entering the slit.

Then look at skylight: you'll see the many Frauhofer absoprtion lines

Then look at different fluorescent light sources: neon tubes, energy saver bulbs, LEDs, computer or TV screens. You might see both emission lines and absorptions.

Lighting the stone:

You need light passing through the stone to be observed with the spectroscope.

For lighting the stone, use a powerful and focused incandescent lightsource from an halogen bulb (fiber optic light source is quite practical if you go for reflected light method, but you might get good results with the transmitted light method using a flashlight).

Whatever you choose just make sure that it does not use a fluorescent bulb (do not use a LED flashlight)

Observation:

Place the spectroscope slit close to the stone. Orientate it so to grab as much light as possible in order to get a bright spectrum. Rotate it so the red is on the left, and the purple is on the right (this is more convenient for comparison with reference spectrum illustrations which are usually represented in this way)

Proceed away from skylight or any fluorescent light source (because all these have a spectrum). That means do not use it in front of a window or in front of your computer screen, or under a neon tube (proceed in a shadowed corner of the room, turning your back to the window, turn off the neons).

Avoid blinding your eyes with the light source before using the spectroscope or you won't be able to notice faint lines.

If you go for the reflected light method, place the stone over a dull black surface.

If you're holding the stone with your fingers, make sure you're not looking at your finger spectrum or finger nail spectrum (which might be mistaken for an apatite spectrum!).

While some stones have a very pronounced spectrum, other have a very faint one that might not get immediately noticed unless watching carefully. Also note that some spectrums are characteristic, but some aren't (thus of no use for identification)

Description of the observed spectrum:

with a graduated spectroscope you can name precisely the wavelengths, but otherwise you might describe things approximatively.

I mean using words like absorption/emission, weak/stong, thin/wide, line, band, doublet-line, complete absorption, cut-off, left/midle/right of red/orange/yellow/green/blue/purple.

Training:

Using a spectroscope isn't all that easy at first, and you need both to practice with stones and learn the theory (so you can understand and interpret correctly what you see).

I would highly recommend a little book named "OPL a students' guide to spectroscopy", by Colin H Winter. It's a good introduction to spectroscope, it explains how to use the spectroscope and the theory behind it, and it also illustrates some of the most characteristic spectrums to be encountered. The website www.geminterest.com also illustrates many spectrums.

13th Jul 2014 10:14 UTCMO

Hi

I would like to know that could I test Spectroscope for rough gemstones?

Thanks

13th Jul 2014 14:08 UTCVandall Thomas King Manager

You can also do qualitative analysis of some major elements using your spectroscope. Mineral collectors, not just gemologists, would benefit from owning and using a spectroscope properly.

13th Jul 2014 19:16 UTCOwen Melfyn Lewis

Sad that as a matter of fashion, so few mineralogists seem to own and used a hand spectroscope. It's well suited to field use. It's limitation is that many minerals do not show a definitive spectrum. But for those that do.....

30th Jul 2014 00:51 UTCDana Morong

I always wanted an old time hand spectroscope. An old friend gave me a spectroscope, but it turned out to be an old large one, prism type on a stand, with 3 tubes (he had used it with some carbon-arc apparatus he had rigged up; he had the time and room to do this set-up). I had a hope that someday I might find someone who was interested in using the big one, and would trade a hand spectroscope for the big one, and use it. Alas, my old friend deceased some years ago; I really appreciated the correspondence we sent back and forth.

30th Jul 2014 10:18 UTCOwen Melfyn Lewis

Dana,

There is a small collectors' market for table spectroscopes. Your best bet is to find out what you can about the one you have (Maker's name, serial no, if any and is it complete?). Then take some decent photos, showing all this and put it up on e-Bay in the scientific instruments section. Watch that marketplace and you will see one sold there about every month or so and that will give you some ides as to what your might fetch in the condition that it's in. These instruments are commonly used for measuring refractive indices rather than recording absorption/emission lines in the optical spectrum.

There are two different small designs for optical spectrum examination. The best value and most frequently recommended is the OPL 'Teaching Model' spectroscope, available from here. http://www.oplspectra.com/index.php?option=com_virtuemart&page=shop.browse&category_id=5&Itemid=32 For a beginner it's recommendable to purchase the OPL stand for this model as well. You will also need a strong white light source (which can be hand held). Do *not* try to use any light source that is LED or fluorescent as the light they emit does not have a continuous spectrum - your light must come from an incandescent source. Also buy their 'Student's Guide to Spectroscopy'; that is both cheap and simply the best guide to the use of a spectroscope (which must be learned and practiced) that is written in English.

These small instruments are only really suitable for the spectrum characterisation of coloured, transparent crystals. For the characterisation of the spectra of opaque materials, you need special illuminating sources and a good spectrometer as opposed to a spectroscope - and will need a budget of several thousand dollars for these. This much more expensive approach opens the door also to examining the interaction of matter with radiating energy across a much wider spectrum of energy radiation (and at ever increasing cost), from X-ray to the far IR.

The modest hand-held spectroscope opens the door to observations and study of the interaction between crystals and energy in the form of light. This is, ultimately, the first door to understanding everything around us. Good luck!.

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