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Diamonds, Spectroscope


#1

Francoise:

Thanks so much for all your recent posts, especially the one on
the diamond spectra. I learn so much from them. I have been
putting off buying a spectroscope, but with the garnet and
diamond ID uses, I think now is the time to buy. I wonder if you
have some recommendations — do I need a wavelength scale or
will something like the OPL (diffraction grating) scope do? I
have dark field and fiber optic light sources available, so only
need the instrumet itself. Thanks for your input and that from
others on this issue.

Roy (Jess)


#2

I have been putting off buying a spectroscope

Hello Roy,

For the majority of their colour is due to one or
more of 8 transition elements within their presence. These
elements are : chromium, cobalt, copper, iron, manganese, nickel,
titanium, vanadium. These elements are present as trace
impurities or also can be an integral part of the gem’s chemical
composition. In both cases, the resulting colour of the gem will
be due to the selective absorption of the wavelenghts in the
light illuminating the gemstone.

The spectroscope spreads out the light from the gemstone into
its spectral colours. In this way it is possible to see the
wavelenghts that have been absorbed as bands or dark lines and
what is missing from the full spectrum. This is called an
absorption spectrum and if distinctive enough will be
characteristic for a particular gem. Because there is no two gem
matyerials that do absorb the same wavelenght in the sane manner
it makes it possible to identify characteristic spectrum for
many gems.

There is two types of spectroscope commonly used : the prism
type spectroscope and the diffraction-grating spectroscope.

The prism type spectroscope : the violet to blue end will be
spread out comparing with the other colours and the orange to red
end will appear compressed, the spectrum seen is not evenly
spaced across the range. A calibrated wavelenght scale will show
number from 400 to 700, with this numerical reading it is easy to
quickly identify a stone by its characteristic spectrum. The
prism spectroscope comes with an adjustable slit which can be
appropriately set for the resolution of the spectrum being
analyzed. It is a costly instrument.

The diffraction-grating spectroscope : it is relatively
inexpensive (around $ 80.). The spectral colours are evenly
spaced out. The spectrum might not be as bright as in the prism
spectroscope. It might be difficult to control the amount of
light that enters the spectroscope.

For its low-price the diffraction-grating spectroscope, used in
conjunction with a fibre-optic light is a very good choice. And
it is extremely portable (I use it with a pinpoint light).

My opinion : I have used both for several years, however I have
an easier time finding my lines on the diffraction-grating
spectroscope (the OPL). A wavelenght scale is very useful as well
as a good book on spectrums to learn your lines, it is also good
to know the chemical composition of your stones.

The spectroscope will provide you with a quick way to identified
loose or set stones, uncut or unpolished materials, stones that
possess a refractive index above the refractometer or difficult
to read. It can identified treated stones and some synthetics.

Practice makes perfect.

Best regards,

Francoise.