CHOOSING A COLOURED GEM
A selection of gems Michael Thornton works with and the factors that determine their value.
Ruby
Emerald
Sapphire
Paraiba
Tsavorite
Opal
Origin
One gem can be sourced from several different origins producing varied colours and qualities. Historical origins are prized and are a main factor on a gem’s overall value.
Supply
With mines being depleted globally, prices for gem material continues to rise.
Colour
A mid-tone, not too dark or light, with strong saturation.
Clarity
Gems are naturally included, those that have few and transparent are prized.
Treatment
Most gems are treated by way of oiling (Emerald) or heat (Ruby, Sapphire, Paraiba) amongst other practices to enhance their purity and colour.
Gems that are naturally beautiful and without treatment are prized, commanding high prices.
Michael Thornton Ltd works with untreated to minor treated gems.
Value
This is driven by supply, colour, origin, and treatment.
GEM DETAILS
Ruby
Rubies - Birthstone of July
Rubies from the Mogok mines of Burma circa 1886 are seen as the finest origin, their vivid red hue due to a strong fluorescence is referred to as ‘Pigeon’s blood red’ in the trade. An alternative source of Rubies are those from the Montepuez mine Mozambique circa 2009 whose hue is a deeper red.
Emerald
Emeralds - Birthstone of May
Emeralds from the Muzo mines in Colombia circa 1538 are seen as the finest origin, with their warm intense green colour. A secondary source of Emeralds are those from the Kagem mine in Zambia circa 2005 whose colour is a more cooler bluish green.
Sapphire
Sapphires - Birthstone of September
Sapphires from Kashmir circa 1880 with mines depleted by 1927 are seen as the finest origin, famed for the velvety blue colour. A secondary source of Sapphire are those from from Burma, whose material is a more intense blue known as ‘Royal’ blue
Paraiba
Paraibas - Birthstone of October
Paraiba Tourmalines from Brazil circa 1980 are seen as the finest origin, the allure is their unique electric neon blue colour brought about by a copper content. Tourmalines from Nigeria and Mozambique circa 2000 are of similar quality with some being given the accolade “Paraiba” type “neon” colour.
Tsavorite
Tsavorites - Birthstone of January / May
Tsavorite’s from Kenya and Tanzania circa 1967 are seen as the finest origin, rarer than Emerald its stunning pure green hues, durability, and purity without treatment.
Opal
Opals - Birthstone of October
Opals from the lighting Ridge in NSW Australia circa 1849 are seen as the finest Opals for their unique play of varying colors, brilliance, and pattern. There are several other types of Opal, such as intense fire opals from Mexico and the Welo Opals from Ethiopia whose vivid colours play within its transparent body.