Inorganic Gemstones

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Chelsea Filter

The Chelsea filter is a dichromatic filter which transmits two wave lengths only - in the red region at 690nm and the other in the yellow region at 570nm. The presence of the elements chromium or cobalt in a gemstone makes it appear red when viewed through this filter.

Uses of Chelsea Filter:

  • This filter normally indicates the coloring elements present in certain gems.
  • Stones coloured by chromium and cobalt will appear red under this filter.
  • In some cases it may help to detect dye in certain stones.
  • It is generally useful for green and blue stones such as emerald and aquamarine.

Procedure:

  • Use strong white light source.
  • Light may be transmitted or reflected from the stone.
  • Hold the filter close to your eye or to the stone; observe the reaction of the stone.
  • It can either be red or green, with secondary shades of pink, brown, yellow, blue or black.

Precautions:

  • Stones should be observed from all directions.
  • The reaction seen through the stone would depend on size, shape, transparency, cut and colour of the stone.
  • Each stone would react differently depending upon the colouring agents present.
  • Chelsea Filter is an indicative test. This test in itself is not a confirmatory test of the stone's identity.
  • Presence of iron tends to retard or dampen the red colour in emeralds, ruby etc. and is responsible for the shade variations.
  • A synthetic emerald with iron content will tend to behave as some natural emeralds, while a natural emerald with high chromium content will exhibit red like some synthetic emeralds.

Some Common Reactions Under Chelsea Filter:

1. Synthetic Emerald (Cr) Red
2. Blue Glass (Co) Red
3. Synthetic Blue Spinel (Co) Red
4. Synthetic Blue Quartz (Co) Pink
5. Natural Aquamarine (Fe) Green
6. Natural Zircon (Blue) Green
7. Dyed Green Chalcedony Red to Orange Red
8. Dyed Blue Chalcedony Red to Pink
9. Natural Emerald (Cr/V/Fe) Pink to Red / Green to Yellow Green
10. Demantoid Garnet Reddish
11. Blue Topaz Blue Green

Did you know?

Jewellery is one of the most bought products online. An estimated $1 billion USD of diamonds are bought annually via the Internet. Over 40 million people use the Internet to trade!

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In Turkey, people fix a piece of amber in the hubble-bubble, dogged by an age old belief that the presence of the jewel would destroy all the germs and no disease would spread, even after many have dragged their puffs from it.

In Greece, people think if wine is poured into the cups made of amethyst, one does not get drunk after drinking that.

In Rome, a talisman having coral pieces is considered very auspicious to quell the bad spells of evil look. The Romans were in the habit of hanging chains made of ancient coral pieces from the cradle of the infants to protect them from evil effects.

In China, people wear rings studded with tiny conch or oyster shells as they believe it cures all aches such as stomach ache, worms and like.

In India, pendants made of silver and studded with pearls are hung from the necks of the children to save them from any bad effects.

Greeks still believe, if women wear blue sapphires then no sense of immorality would pollute their mind nor can any fear of the supernatural can trouble them.

The Pope Innocent III had circulated an order asking all the priests wear blue sapphire, so that morality can be strengthened.

It is said about turquoise, that when the stone changes its color into yellow, it actually signals bad times to the person who wears it.

It is believed that a turquoise gifted to a friend or a lover turns his or her life into one of happiness and good luck.

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