Physical properties of Gemstones

Physical properties of Gemstones
The physical properties of gemstones, their hardness, their specific gravity or density and the way they break or “cleave”, depend on the chemical bonding and the atomic structure of the stone.
1. Hardness
2. Cleavage
3. Fracture
4. Specific Gravity
5. Crystallography
1.Hardness
Hardness of stone is measured by moh’s scale. It is best defined as a property possessed by a substance to resist abrasions when a pointed fragment of another substance is drawn across it.
2.Cleavage
Cleavage is the tendency of a crystallized mineral to break in certain definite directions, giving more or less a smooth surface.
3.Fracture
When a gemstone breaks along a surface that is not related to its internal atomic structure, it is said as a fracture. Fractured surfaces are generally uneven, and each has its own descriptive name.
4.Specific Gravity
Specific Gravity (SG) of a gem stone is an indication of its density. It is calculated by comparing the stone’s weight of equal volume of water. The greater the stone’s specific gravity, the higher it will feel.
5.Crystallography
Crystallography is a science of crystals. The properties by which gemstones are identified are entirely based upon its basic crystal structure. Rough crystals themselves are very beautiful and well formed crystal. It displays characteristics features such as cleavage surface, marking forms etc.

Instrument used for gem identification

Instrument used for gem identification

1. Microscope and 10z loupe
2. Refractor meter is used for finding refactrative index of the stone.
3. Dichroscope is used for finding out the properties of trichroism, diachronic and pleochroism.
4. Spectroscope is used or finding out the wave.
5. Ultra violet lamp is to detect the fluorescence and phosphorescence.
6. Choelsea filter is a dichromatic filter, which transmits Z wave’s lengths.

Moth’s scale

The hardness of stones is measured by the scale is called Mohs’ scale, named after Friedrich Mohe, a German mineralogist (1773- 1839.)If is based on the ability of one stone to be scratched by another, or to itself be scratched.

Scale

Category Family name
1. Talc
2. Gypsum
3. Calcite
4. Fluorite
5. Apatite
6. Orthoclase
7. Quartz
8. Topaz
9. Corundum
10. Diamond

Gem Stones- Lusture & Dispersion

LUSTRE: The quality of light reflected off the surface of a stone .Use reflected light to judge.
- Metallic: Metal-like the highest possible luster .e.g. Hematite, Pyrite.
- Adamantine: The highest possible luster for gemstone .e.g. Diamond, Zircon, Dermatoid Garnet.
- Vitreous: Glass- like the most common luster for gemstone. E.g. Quartz, Beryl, Topaz.
- Greasy: An oily appearance; common for jade. Also seen in some garnets, peridot etc.
- Resinous: Similar to greasy; used to describe the luster of amber.
- Waxy: Little reflection; similar to the luster of a candle or a fingernail. E.g. Turquoise, Chalcedony.
- Dull: Very irregular, fine- grained surface; common on unpolished, opaque stones. E.g. rough Turquoise, Malachite.
- Silky: Reflection off fibrous structure (sheen), e.g. Tiger’s eye.
- Pearly:Due to structure (sheen); common to Pearl, rough moonstone, cleavage surfaces etc.

Dispersion: The breaking of white light into its component spectral colors.
- Observed as flashes of spectral colors, known as fire.
- A few stones have eye- visible dispersion which can be a useful identifying characteristic.
- The presence or absence of dispersion in diamond stimulants is important in their identification (e.g. strontium- titan ate – very high dispersion, YAG –barely visible dispersion).

Jewelry Designing - Parts of Gem Stone

Different Parts of stones-:
Crown
1.Table
2.Star facet
3.Bezel facet, crown main facet
4.Crown griddle facet
5.Griddle
Pavilion
1.Pavilion main facet
1.Culet
Entire form
1.Crown
2.Pavilion

Jewelry designing- Gem stones

Gemstones used in jewelry are given values based on their weight, size, luster, brilliance, transparency, and stones degree of perfection, durability, portability and availability. The relative rarity of stones possessing some or all these qualities has resulted in the classification of gemstones into precious and semi- precious groups.

Precious Stones
There are nine precious stones-:
1.Diamond
2.Ruby
3.Emerald
4.Blue Sapphire
5.Yellow Sapphire
6.Coral
7.Cinnamon
8.Cat’s eye
9.Pearl


Semi precious stones- All other stones believed to be sufficiently attractive when cut and polished to be usable in jewelry are considered semi precious.

Synthetic stones- Today science has devised ways of manufacturing many gemstones by artificially reproducing their crystal structure, and the results are termed synthetic stones.

Color:Color is considered by its hue, tone and saturation.
Hue- pure spectral colors.
Tone- That attribute by which a color is perceived as holding a position on a scale from light to dark.
Saturation- Measurement of the amount of hue in a color
• Color is also considered in terms of a primary and a secondary shade. E.g. bluish green.
• These factors depend essentially on the type of light used .The same stone may behave differently in different light sources.
• The light source should be daylight with a preference for north light (less U.V. radiations).
• The stone should be examined in reflected white light initially. And then in transmitted light.
• Over colored Stone tuned to give misleading idea of transparency. Due to the intensity stone would appear opaque in reflected light


Transparency: The quantity and quality of light transmitted by the stone. Use transmitted light to judge

Transparent(TP)- Transparent stone usually are cut with facets to allow maximal dispersion of light within the stone. The quantity and quality of light transmitted by the stone. Transmits light readily; can read through easily, even if colored. E.g. diamond, ruby emerald etc.

Opaque(OP)- Opaque stones are generally cut in cabochon. Transmits no light .E.g. Pyrite, Hematite, Laces Lazuli.

Translucent(TI)- Translucent stones may be cut either way. Transmits a very small amount of light. Primarily around the edges. E.g. star garnet.

Semi-Transparent(S-TP)- Transmits light somewhat less readily; can read through but with slight distortion (Somewhat hazy). E.g. Amber and moonstone.

Jewelry Designing - What is a Gem Stone?

• To identify a gemstone there are a number of very accurate tests which a jeweler-gemologist can make use of.
• Each gem species has characteristic physical and optical properties which are constant
Within narrow limits and to a certain extent can be objectively determined.
• However, a basic fact which must never be forgotten is the importance of a visual identification.
• An unknown stone can be classified by correctly perceiving its color, cut transparency,
Luster, dispersion, heft, as well as any phenomenal properties etc.
• The type of lighting in which each of the properties is observed is also important.

What is a gem stone?
Beauty, Rarity & Durability: B, R, D, is one of the basic concepts by which a
Material can be defined as a gemstone.

Beauty: This is a subjective property and is defined by the four C’s’, Color, Clarity,
Cut and Carat size. The presence of a phenomenon also enhances the beauty of a gemstone.
- Color: In colorless stones, the lesser the color the better the quality. In colored stones, the darker and purer the shade of color, the better the quality.

- Clarity: This is defined by the presence or absence of inclusions within a stone which indicates the transparency. This can be more objectively judged by.
- Number of inclusions
- Size of inclusions
- Position of inclusions
- Color of inclusions

- Cut: A stone which has been cut and polished keeping in mind the accurate angles and proportions of cutting, which bring out the full life, fire and brilliance of a gemstone. The beauty of a particular cut can be observed by examining the type of cut. And the summery and polish on the crown, pavilion and girdle portions of the stone.

- Carat size: This relates primarily to the weight of a stone.

1 carat = 100 cents / points =200mg.
The larger the size, with good color and clarity, the higher the value.
Weight of the gems, i.e. larger the stone with good color and clarity, higher the value.

Rarity : The is an important aspect and may either be due to natural resources or due to man made situations.
- If a gemstone is available in large quantities, it will not be much in demand.
- If a gemstone has all the four C’s’ and a phenomenon, it would be rare.
- Political and economic conditions in country can control the supply to demand ratio of rough and cut stones.
- If a stone has a limited geological and geographical occurrence i.e. from a single source e.g. red beryl from Utah (USA)

- Durability: A gemstone must be durable enough to withstand dally wear and tear. This includes the qualities of hardness, cleavage, brutality toughness resistance to heat pressure or chemicals.

- A softer stone will get scratched more easily.

- A stone with a number of internal cracks will be less durable.

- A stone with easy cleavage e.g. diamond topaz etc. may split into two if it suffers a hard knock.

- Perspiration, perfumes lime juice etc. may damage less resistant gem materials such as pearls.

Jewelry Desining- Working with Rotring Pen

Day9 to day 15-
As we are perfect with the basic patterns of jewelry, we take a step ahead and learn something more interesting. Before we start with the next chapter we need some stationery like Rotring pen, Black ink, Inject sheet, Mount board, A4 Tracing sheet, clips and mix template.
Another thing to keep in mind is how to use the rotring pen? As this pen is very delicate we need to take care of few things while using it.
• Before pouring the ink in cartridge, it should be well cleaned and dry.
• The cartridge bottle should be filled at ¼ level.
• Before using the pen it should be shake well, but very delicately.
• The tip of the pen should be well cleaned before and after working.
• If the pen is not being used for more than 5 days then the pen should cleaned well. The ink should be transferred back to the ink bottle and should be well cleaned with the water. Make sure the pen tip is also cleaned with water. It should be well dried in shade and on a soft base.
Now coming back to the learning part, on the inject sheet draw different shapes with the help of the mix template. Now using the rotring pen over these shapes. The movement of the pen should be in flow and no over lapping should be there. The movement of the pen should be very soft.
On the other side start using tracing sheet to trace some good design from any jewelry design book. This helps one person to have a good flow in designing part, along with the drawing part.
The very next step is to trace out the designs from tracing sheet to the inject sheet. The traced designs on the sheet need to be given a perfect, proportional shape with the pencil and then do the rotring pen on it. Along with this we need to draw symmetrical image in the inner side of the original image maintaining equal distance with rotring pen. The inner lines should not be wide at all. This chapter is the most important of all as this will help with designing and it will help you from scratch till the end of jewelry designing and this is the main base of jewelry designing.