The world of gems is a very important topic for my profession as a jewelry designer. As I am not an expert in the field, I try to train myself as best as possible in this field. Therefore I read everything that comes to my hands regarding this exciting world of gems.
This week I wanted to leave you an interesting article published by the specialized newspaper, in its edition of September 2011. In it they develop a summary of the main parameters used for the graduation and classification of precious gems.
So that these readings serve as learning for those interested in the subject, I go on to write the article.
“Within the complexity that exists to grade and value colored stones, due to the lack of universal recognition methods, a classification prepared by the Spanish Gemological Institute has been chosen, looking for easily recognizable references and nomenclatures in the trade.
The main parameters that are taken into account when grading the quality and assessing the colored stones are the following: color, purity, cut quality, weight and presence of treatments.
The color of the gems is graduated by two parameters: tone, type and intensity.
Typical hue – equivalent to the dominant color hue. The name of the type tonality corresponds to the most characteristic source deposits for this tonality. These names should not be understood as a reference to the origin of the stone.
Emeralds : two standard shades are established:
A – the characteristic color tone for Colombian emeralds, which can also occur in stones from other deposits. Best hue for emeralds.
B – shades different from shade A, typical for emeralds that come from the deposits of Brazil, Africa and others, although they can also be observed in some Colombian emeralds.
Rubies : two standard shades are established:
A – the characteristic color tone for rubies from ancient Burmese sites (Mogok), which can also occur in rubies from other sites. Best hue for rubies.
B – shades other than shade A, typical for rubies that come from deposits in Thailand and others.
Sapphires : three typical shades are established:
A – the color tone characteristic for sapphires from Burma or India (Kashmir), although it can also occur in stones from other deposits. Best hue for sapphires.
B – the characteristic shade of blue for Sri Lankan sapphires, although it can also occur in stones from other deposits.
C – the shades other than shades A and B, typical for sapphires that come from the deposits of Australia and others.
Intensity – characteristic that reflects the saturation and darkness of the color, with the best colors being the most intense and the worst being the lightest and also too dark. There are five degrees of Intensity, from A to E.
It is graded with the naked eye, using the table of five degrees of gem purity, from stones with no or very few inclusions (A) to stones that are practically opaque due to the abundance of inclusions (E).
Once the Color and Purity parameters have been established, we can select the commercial category corresponding to each stone using the table of equivalences. For example, an emerald of Tone type A, color intensity C and purity B corresponds to the Commercial grade A +.
Carving quality is graded at a glance, taking into account the following parameters: proportions, symmetry and polishing quality. The Gold & amp; Time are crafted for Good cut quality gemstones. For other grades of cut, the following correction coefficients are used for the price per carat: Excellent (+ 20%) – Very good (+ 10%) – Good (0%) – Medium (-15%) – Poor (-30% ).
The International Jewelery Confederation (CIBJO) differentiates two types of treatments:
1. Those that only require general information from the buyer about the treatment applied. They are less serious and commonly accepted commercial treatments. The treatments classified in this group are:
* Filling of fissures with colorless non-vitreous substances.
* Superficial impregnation with colorless substances.
* Warming up.
* Bleached (for pearls)
2. Those that require specific information from the buyer about the treatment applied to the gem. When making the sale, the buyer must be unequivocally informed that the gem that is being sold is treated by a certain process. In this group are all other treatments, such as irradiation, dyeing, coating, etc.
In general, the most accepted treatments that only require general information do not influence the price of the gems, since most of the stones in the trade have this treatment (for example, fissure filling in emeralds or heat treatment in rubies and sapphires) . In this way, the average market price is established for stones with these generalized treatments. On the contrary, gems that show signs of not having been treated in any way have a significant price premium compared to the average prices (up to + 50% for emeralds without fissure filling, + 50% for sapphires without heating and + 100% for rubies without heating).
Well, I say goodbye this week trying to bring you closer to this passionate and curious world of gems.