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The fact that graptolites, and many other organic-walled fossils that are opaque to visible light, may be
transparent to infrared radiation has been known for many decades. However, infrared photomicrography has
not gained widespread use among graptolite specialists, presumably as a result of the difficulties in obtaining
satisfactory images that revealed structures of interests. The growing importance of fusellar growth bands and
internal structures as they relate to astogenetic patterns and colony growth has lead to the search for a new
way of using IR radiation that reveals these features non-destructively, in as wide a variety of specimens as
possible.
Infrared video microscopy (IVM) uses a relatively inexpensive video camera that is sensitive through the visible
and near IR range, up to wavelengths of 1300 nm. This camera can be connected to a normal biological or
petrographic microscope. The best results are obtained when visible light is filtered with a 1000 nm, longpass
filter, although the crossed polarizers on a petrographic microscope can serve a similar function. The images
obtained can be viewed on a video monitor, printed by direct connection to a video printer or else
electronically stored using a computer video image capture system. The stored images can then be analyzed
using image analyses software, printed or photographed through a slide-making system.
Provided the specimens are not of high thermal alteration or very thickly covered in cortical tissues and are
not covered or infilled with IR-opaque mineral material, the resulting images reveal surface morphology,
fusellar banding (and occasionally cortical bandages) as well as all internal walls and structures. Optimum
image quality requires that the specimens be immersed in a very high refractive index liquid, preferably 1.76,
the refractive index of the graptolite periderm material. The best visualization of internal structures can be
achieved using stereo-pairs of prints of the video images. These can be obtained by using a universal stage
and tilting the specimens ca. 8 degrees between prints.
transparent to infrared radiation has been known for many decades. However, infrared photomicrography has
not gained widespread use among graptolite specialists, presumably as a result of the difficulties in obtaining
satisfactory images that revealed structures of interests. The growing importance of fusellar growth bands and
internal structures as they relate to astogenetic patterns and colony growth has lead to the search for a new
way of using IR radiation that reveals these features non-destructively, in as wide a variety of specimens as
possible.
Infrared video microscopy (IVM) uses a relatively inexpensive video camera that is sensitive through the visible
and near IR range, up to wavelengths of 1300 nm. This camera can be connected to a normal biological or
petrographic microscope. The best results are obtained when visible light is filtered with a 1000 nm, longpass
filter, although the crossed polarizers on a petrographic microscope can serve a similar function. The images
obtained can be viewed on a video monitor, printed by direct connection to a video printer or else
electronically stored using a computer video image capture system. The stored images can then be analyzed
using image analyses software, printed or photographed through a slide-making system.
Provided the specimens are not of high thermal alteration or very thickly covered in cortical tissues and are
not covered or infilled with IR-opaque mineral material, the resulting images reveal surface morphology,
fusellar banding (and occasionally cortical bandages) as well as all internal walls and structures. Optimum
image quality requires that the specimens be immersed in a very high refractive index liquid, preferably 1.76,
the refractive index of the graptolite periderm material. The best visualization of internal structures can be
achieved using stereo-pairs of prints of the video images. These can be obtained by using a universal stage
and tilting the specimens ca. 8 degrees between prints.
| GRAPTOLITE NET is edited and periodically updated by Piotr Mierzejewski, Count of Calmont and Countess Maja Korwin-Kossakowska since 2002 |
| INFRARED VIDEO MICROSCOPY FOR THE STUDY OF ISOLATED GRAPTOLITES Michael J. Melchin, Peter Berridge and Alan J. Anderson Graptolite News 1995, 8, 49 |
