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MICROSCOPY

Mel Wachowiak


Image of Cross Section Image of Cross Section UV Light

Top Image: Cross-section of 19th century painting on canvas, 25x magnification, darkfield illumination. Linen canvas weave visible at the bottom of the image, red ground and paint layers above. Bottom Image: Same painting cross-section at 25x, illuminated with ultraviolet light. Linen canvas structure is easily seen in contrast to mainly inorganic pigments of ground and paint layers.

Compound Light Microscope

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°.



Reflected Light

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.


Transmitted Light

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.


Sample Preparation Videos: Embedding and Sample Preparation

These videos cover several procedures for embedding, mounting, and polishing samples for microscopy based on the above publication. Standard laboratory procedures were used to embed and polish samples for microscopy. Details published of the method and materials can be found in Wachowiak M. J. Efficient New Methods for Embedding Paint and Varnish Samples for Microscopy.



Imaging

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.



Photomacroscope

Image of Space Suits

Low-powered magnification of lunar dust on Apollo suit of astronaut Jack Schmitt, who walked on the moon in December 1972 (collection Smithsonian National Air and Space Museum). Image at right: front of suit worn by Jack Schmitt. Top left: sample location on right sleeve (scale bar=1 cm); center left: detail of area above (bar=1mm); lower left: area of image above in greater detail (bar=1mm). [Photo: Smithsonian National Air and Space Museum]

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.


Image of Space Suits

Detail of Apollo Teflon test fabric from the collection of the Smithsonian National Air and Space Museum.


Further Reading

Lunar Dust on Apollo Spacesuit Systems Summary

NASA's Lunar Dust Effects on Spacesuit Systems



Montage of African Beads

Left Image: A 4mm wide bead from collection of National Museum of African Art. Series of over 30 images were processed using multifocus technique to produce a single image of much greater depth of field. Note difference in focal plane from upper left to lower right. Right Image: A single composite image computed from only in-focus areas of over 30 images. Image can also be used for interactive measurement and 3D reconstruction.


Further Reading

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