The emerald filter

The emerald filter, also called" CHELSEAFILTER " may possess a practical quality that many seem to ignore. In many cases it can give an indication about the nature of the stone, not only for the green colour stones, imitating the emerald but also for other colour stones. Together with the achromatic and aplanatic loupe of 10x magnification, this little instrument can be easily put into the pockets and finds in this way its utility while going here and there.

To use the emerald filter, one preferably places the stone under a strong white light place de (daylight 100 watt) and one observes the stone looking through the filter.

Take notice however that this instrument has to be used with reserve as to the conclusions : the different shades of colour vary quite a lot and their appreciation may depend on the eye of the observer. In no way the filter allows a definite determination.

Below, a table with the principal stones classified according to colour (blue, yellow or orange, violet or purple, red or pink, green)

BLUE STONES :

Natural sapphire, synthetic sapphire	Black or slightly blackish-green (certain artificial stones give dark green-reddish)
Synthetic sapphire, alexandrite colour	Reddish
Spinel	Greenish
Synthetic spinel : dark blue or alexandrite colour	Red
Synthetic spinel : zircon blue colour	Orange or red
Synthetic spinel : aquamarine colour	Orange
Aquamarine	Greenish
Lapis-lazuli	Black
Lapis-lazuli artificial	Red
Tanzanite	Red violet
Topaze	Green to greenish
Tourmaline	Green to greenish
Zircon	Green to greenish
Glass : light blue	Greenish or pink
Glass : vivid dark blue	Red
Glass : greyish dark blue	Greenish

YELLOW OR ORANGE STONES

Beryl	Greenish yellow
Citrine	Greenish yellow
Corundum : natural or synthetic	Golden yellow
Hessonite and Spessartite	Brown
Synthetic Spinel	None
Topaze	Greenish
Glass	Yellow

VIOLET OR PURPLE STONES :

Amethyst	Yellow or red
Corundum : natural or synthetic	Vivid red very fluorescent (*)
Fluorite	Reddish
Almandine garnet	Red
Spinel : natural or synthetic	Vivid red (*)
Tourmaline	Yellow to green
Glass	Greenish yellow

RED OR PINK STONES :

Garnet	Dark red (Pyrope more pronounced than Almandine or Rhodolite)
Kunzite	Pink
Morganite	Pink
Ruby : natural or synthetic	Vivid red fluorescent (*)
Spinel : natural or synthetic	Red fluorescent (*)
Tourmaline	Red or pink
Glass	Red

GREEN STONES :

Alexandrite	Red
Chrysoberyl	Green
Natural Corundum	Green
Synthetic Corundum	Red or green
Demantoïde garnet	Red or pink
Opaque grossular garnet	Green
Transparent grossular garnet	Yellowish green
Hydenite	Green or orangy green
Jadeite	Green
Jadeite tinted	Red
Peridot	Red to pink; sometimes greenish blue
Natural spinel	Green to brownish green
Artificial spinel	Green or red
Tourmaline	Green
Tourmaline with chrome	Red
Zircon	Red , brownish red or pink
Quartz	Green, yellow
Quartz aventurine	Green or reddish
Chrysoprase	Green
Agate tinted chrysoprase colour	Generally red
Beryl	Green
Emerald	Pink to red (India : green, Brazil : yellow)
Emerald : synthetic or artificial	Vivid red (also orange or olive)
Glass and doublets	Green
Triplets	Green or red.

(*) More intense for synthetic than for natural stones.