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.

Diamond Cut: BAROCUT

The Barocut is considered rectangular modified cut with 77 facets-81 in cut corner style. The cut is also perceived as "The Two Heart Diamond" due to the look of two hearts meeting point to point deep into the culet of the diamond.

The Barocut diamond brand is the creation of Baroka Creations Inc.

Chemawinite

Garry Platt writes:

Amber from the Cretaceous is rare, but Canada has some remarkable deposits originating from this age. Cedar Lake in Manitoba is probably one of the most commonly written about sites. The Cedar Lake deposits were found on the South West lakeside shore as washed and tiny pieces ranging from .5cm to 2cm in diameter. Highly fossiliferous by all accounts containing many examples of both flora and fauna.

Various scientific expeditions have brought back several hundred pounds of amber from this site. In the 1950’s a project was set in place to begin commercial development of the site. The venture later failed. This site has now been lost to science because of the flooding of the area. The former lake side shore is now hidden beneath the new water level. Reports have been made of amber beginning to appear on the new higher shoreline. So far these reports have been unsubstantiated.

More info @ http://www.gplatt.demon.co.uk/typesof.htm

How The Spectroscope Works

The spectroscope splits visible light into its component colors (using either a set of prisms, or in the less expensive models, a diffraction grating) producing essentially the colors of the rainbow--red, orange, yellow, green, blue and violet. A diffraction grating spectroscope achieves this by using a finely ruled grating consisting of a series of photographically etched parallel lines (as many as 1000 per millimeter) on a sheet of glass. This produces a series of spectra by diffraction and interference, but only the strongest spectrum is used. For proper viewing of gemstone spectra a concentrated light source is required.

Lighting and Use
With an adjustable slit spectroscope, resist the temptation to open the slit wider than it necessary as it only tends to make matters worse by drowning the spectrum with too much light. Instead, try moving the stone to let more light through it, or use a lens to further concetrate light into the stone.

The difficulty in reading lines, bands or absorption in the blue violet end of the spectrum can be overcome, in some instances, by filtering the incident white light through a flask containing a solution of copper sulphate and distilled water (copper sulphate is toxic, so care is necessary when handling it). By filtering out the distracting longer wavelengths (red, orange, yellow, etc) the eyes adjust more readily to the subtle differences seen in the blue violet end.

Inability to see a spectrum may be due to the fact that only a small trace of the spectrum causing agent is present, or that insufficient light is reaching the spectroscope for analysis (e.g , in very dark stones or semi-translucent to opaque material). In very pale or shallow stones, try passing the light through the maximum amount of material in order to enhance the strength of the absorption pattern seen.

Keep in mind
Not every stone has a spectrum, and not every spectrum you see is helpful in gem identification. More important--don't expect all spectra to look as neat and tidy as those illustrated in books. In stones with different selective absorption (dichroic or trichroic) the spectrum may vary depending upon the direction in which the stone is viewed. Spectrum analysis is only one test leading to positive identification of a stone.

How To Judge Chatoyant Stones

There are many gemstones that can show chatoyant phenomena, but the cat’s eye of a fine chrysoberyl combined with the stone’s excellent hardness and durability designate it as the precious cat’s eye among gems.

In the trade, the term cat’s eye alone will always refer to chrysoberyl unless another species is mentioned as a qualifier such as quartz cat’s eye, tourmaline cat’s eye, diopside cat’s eye, kornerupine cat’s eye, etc.

Chatoyancy is a reflection effect from oriented parallel fibrous inclusions or cavities. Light reflects off these needles and if the stone is cut correctly, this results in a single sharp band of light running across the top of the stone similar to a cat’s eye. The domed surface of the cabochon acts like a lens to focus the eye. The grading of phenomenal stones involves the judging of the phenomenon itself as well as the other components that make up the accurate grading of a gemstone.

There are five factors to consider when judging the quality of a cat’s eye.

- The cat’s eye itself

Is it sharp and intense? Is it wavy or even and well-centered? Does it extend from girdle to girdle, and is it properly orientated? Does the eye run lengthwise? Does it open and close?

- Does the stone have good body color?

Is the body color desirable?

- Does the stone have good transparency?

Is there good transparency without sacrificing the sharpness of the eye? There is a very delicate balance in maintaining transparency, yet not being so transparent that the sharpness of the eye is weakened. The base of highly transparent cabochons is often left unpolished for this very reason.

- Does the stone have good clarity?

Are there imperfections, internal or on the surface that interfere with the eye? Do the imperfections distract the viewer from the eye, or decrease the transparency of the stone?

- Is the cutting good?

Is the cabochon shape pleasing to the eye? Are you paying for excessive weight below the girdle that will not be visible when viewed face-up?

Fracture, Cleavage, Parting

1. What is fracture?
Fracture is an uneven break in a gemstone.

2. What is cleavage?
Cleavage is an uneven break parallel to a crystal face due to weakness in molecular bonding.

3. What is parting?
Parting is a breakage due to structural weakness either caused by inclusions or areas of twinning.

Toughness

1. What is toughness?
Tenacity is defined as toughness. By definition it is a measure of resistance of a gem to breaking or fracturing.

2.What is the relation of hardness and tenacity?
They are not related. Hard stones are not necessarily tough. Diamond, the hardest, cleave while nephrite, which is not hard, is very tough.

Hardness

1. What is hardness?
Hardness is defined as resistance to scratching.

2. What scale do we use to judge it?
The Moh's scale.

3. List the order of increasing hardness on the scale with an example at each level.
Talc(1), gypsum(2), calcite(3), fluorite(4), apatite(5), orthoclase(6), quartz(7), topaz(8), corundum(9), diamond(10).

4. What is considered to be the minimum acceptable hardness for a gemstone?
7. Stones with a hardness less than 7 will scratch more easily so how they are fashioned into jewelry and how they are cared for is important.