Microscope

What Are The Primary Functions Of Microscope?

The primary function of microscope is to enlarge the image under view in order to help differentiate between natural and synthetic. Inclusions can indicate not only whether a material is natural or man-made, but also help identify the geographic origin of natural stones as well as the method of formation of those produced in a laboratory.

Natural: crystal, liquid and gaseous inclusions, or a combination of the aforementioned (e.g., two-phase (liquid + gas), three phase (mineral + liquid + gas), negative inclusions, straight color zoning, oriented silk (chatoyancy and asterism).

Man-made (synthetics and artificial stones): inclusions due to growth conditions which are for the most part dissimilar to those found in natural material. For example:
- Melt synthetics (flame fusion, pulling method, floating zone): curved color zoning; unmelted particles, gas bubbles like tadpole, dumb bell in shape or circular bomb-like, are common, but new specimens may be relatively clean.
- Solution synthetics (flux): primary and secondary flux inclusions, platinum platelets, twisted veils, phenakite crystals (emerald); paint splash-like, mesh-like flux, platinum platelets (corundum); (hydrothermal) nail-like, cuneate forms (phenakite crystal and growth tube), growth zoning patterns (chevron-like, wheat stalk-like) liquid and multiple phase inclusions in wispy or fingerprint patterns, metallic inclusions in the form of gold platelets or grains from gold-lined autoclaves or platinum crystals, seed crystals, if any.

Paste: air bubbles, swirl marks, incomplete color mix. Specialty glasses like aventurine glass, slocum stone, rhinestone, foilbacks,etc.,

Assembled (composite) stones (doublets + triplets): squashed bubbles in plane of join, difference in color, inclusions, luster in various sections.

Pearls (cultured and imitation): filled glass bead or coated bead (imitation), drill hole discontinuity layer.

Artificial treatment: heat treatment—strain halos around inclusions, double girdle (polished and fireskin sections: corundum); surface diffusion— revealed by immersion, dark rim, bleeding of color into pits, uneven color due to reploshing (magnification not essential: corundum); fracture filling—dispersion flashes, gas bubbles, color of the compound (emerald); glass filling—difference in luster, gas bubbles (corundum); beryllium treatment—color spots, cottony-like crystals, color rim, melted crystals; lead glass filling—dispersion flashes, melted crystals, color irregularities (corundum, diamond); staining—color build up in cracks and flaws; Irradiation—irradiation stains, cyclotron umbrella-like color in diamond, etc.,

General observations: The observation of external gem features such as luster, quality of cut (symmetry) and polish (condition of facets), detection of breakage (fracture and cleavage) or gem vulnerability to damage, detection of doubling in double refractive stones (indicating the amount of birefringence).

The microscope may be further adapted in conjunction with additional equipment to carry out the following functions:

Polariscope: with the aid of two suitably placed Polaroid sheets—SR/ADR and DR/Aggregate reactions may be noted. Interference figures—a convergent beam of polarized light along an optic axis may produce figures indicating uniaxial or biaxial nature of a DR stone. In addition, the optic sign may be deducted from these figures using accessory plates (e.g., mica plate or quartz wedge).

Pleochroism: using one polar (or two polars side by side with the vibration directions at right angles to one another) while the stone is rotated; it may be possible to note differences in color.

Refractive index: accurate and/or approximate R.I may be determined by the following methods. Real & Apparent Depth Method (R.I = real depth / apparent depth); Immersion Contrast; Becke Line Effect (simplified Becke).

Spectroscope: by fixing a spectroscope in place of an eye piece and observe absorption and emission patterns.

Plato Method: for distinguishing between pale colored natural and flame fusion synthetic corundum when characteristic inclusions are not noticeable (in di-iodomethane—methylene iodide), view along optic axis through crossed polars at 30x, dark lines intersecting at 60º indicate synthetic; in most cases, natural stones won’t show lines.

Photomicrography: fix camera adapter in place of an eye piece to record inclusions for further study or reference.

Other: measurement of stone using calibrated stage; measurement of interfacial angles using rotating stage.