MCI Imaging specialists have been using a number of imaging techniques to document and help understand the nature of cultural heritage materials. These techniques record variations in scale from micro to macro, two- and three-dimensions, light interactions beyond human vision, and so open up new ways of seeing.
MCI is capable of supporting documentation and research using light microscopes that magnify from 3x to 1000x.
Reflected and Transmitted Darkfield, Brightfield, and Fluorescence Microscopy
The DMRX materials research microscope at MCI is capable of several reflected and transmitted light techniques, in sequence, or simultaneously in some cases. The frame is designed for materials science applications (metallurgy etc.) so large and heavy specimens can be placed on the stage. The translating stage can hold specimens several centimeters high, weighing more than one kilogram and can be rotated through 135°.
The range of magnification for the reflected light techniques is 50x to 500x, measured at the eyepieces. Objectives are 5, 10, 20, 40, and 50x. Through the use of a prism system, brightfield and darkfield illumination conditions can be alternated. The tungsten halogen lamp is the source of reflected light and it is corrected for daylight color temperature using a dichroic mirror. The fluorescence illuminator is either 100W mercury or 150W xenon lamp. The filters span the range from ultraviolet to the violet. The DMRX is also equipped for reflected differential interference contrast (DIC) microscopy.
The range of magnification for the transmitted light techniques is 25x to 1000x, measured at the eyepieces. Objectives are 2.5x, 5, 10, 20, 40, 50 and 1000x. The tungsten halogen lamp is normally the only source of transmitted light and it is corrected for daylight color temperature using a dichroic mirror. Qualitative polarized light can be used with transmitted light.
Standard laboratory procedures were used to embed and polish samples for microscopy (details of the method and materials can be found in Wachowiak M. J. Efficient New Methods for Embedding Paint and Varnish Samples for Microscopy.
A purpose-built digital camera is used for image acquisition. Camera chip dimensions, as well as pixel count, determine ultimate magnification of image. The camera systems used include Leica EC3 3.1 megapixel, or Leica 420C 7 megapixel 24-bit color systems. The systems are calibrated using a stage micrometer and scale, and x, y and z axis measurements can be made. Image information can be further processed with the Leica Application Suite, including extended depth of field imaging.
MCI uses a highly specialized photomacroscope to produce high quality images (from 3x-115x), including 3D reconstructions, anaglyphs, high dynamic range images, as well as digital movies. The Leica Z16APO also uses the 420C camera listed above. Leica Application Suite suite controls the movement of the camera and optics. The Montage software creates 3D reconstructions from images collected along the z-axis. The Leica 3D view Module allows viewing and exporting 3D images. The Mult-Time Module is used for creating streaming video and movie export.
The microscope is also equipped with a brightfield coaxial illuminator that produces a reflected brightfield effect similar to materials science microscopes. The unique arrangement of the optics allows projections of the light along the optical axis.
The microscope was purchased from funds provided by the Smithsonian Women’s Committee in 2008.
Efficient New Methods for Embedding Paint and Varnish Samples for Microscopy
by Melvin J. Wachowiak Jr.
The Application of X-ray Fluorescence (XRF) Spectrometry in the Characterization of Glass Degradation in Beaded African Art by Maria Fusco and Robert J. Speakman