Microscope Slide — The Glass Substrate Beneath the Coverslip
Microscope Slide — The Glass Substrate Beneath the Coverslip
Standardised 75 × 25 mm glass for mounting gem fragments and thin sections
A microscope slide is a flat rectangular glass plate, standardised at 75 × 25 mm with a thickness of 1.0 to 1.2 mm, used as the substrate for mounting specimens for transmitted-light microscopy. In gemmology, slides are encountered when extracted inclusions, surface fragments, or thin sections of gem material are prepared for high-magnification examination and photomicrography.
Standards and variants
The 75 × 25 mm format is universal for biological and gemmological work; 75 × 50 mm is sometimes encountered for larger specimens. Slides are sold plain or with one frosted end, the frosted area providing a writing surface for specimen labelling in pencil. Edges may be ground and bevelled (the higher-quality option) or simply cut. Pre-cleaned slides come dust-free and ready to use; bulk slides require cleaning before mounting any specimen for archival photography.
Use in gemmology
The most common gemmological application is mounting an inclusion fragment that has been extracted from a stone — typically from a fragment lost during cutting or from a damaged stone where the inclusion can be released by fracture. The fragment is placed on the slide with a drop of immersion oil or appropriate mounting medium, covered with a coverslip, and examined under a compound microscope at magnifications well above the 80× ceiling of a typical gemmological stereo microscope. Element analysis, Raman spectroscopy, and microprobe work often follow.
Thin-section work is less common in commercial gemmology than in research mineralogy but does appear, particularly for opaque or near-opaque materials whose internal structure can only be observed in transmitted light through a section of approximately 30 microns thickness.
Handling
Slides must be free of dust and oil before specimen mounting; any contamination will appear in photomicrography and may obscure diagnostic features. Cleaning with isopropanol on a lint-free cloth before use, and storage in a dust-free slide box, are standard practice. After examination, slides with valuable specimens are sealed and archived for future reference.