یکشنبه 28 آبان ,1396
02:39

Turquoise Grading in Persian historical and modern times; a comparative study

[24 آگوست, 2017]

Masoud Ovissi1, Mohammad Yazdi1, Mansour Ghorbani1*
1 Faculty of Earth Sciences, Shahid Beheshti University, Tehran, Iran
* Corresponding author; Email address: m-ghorbani@sbu.ac.ir

Abstract
In fifth and sixth centuries A.H., Seljuk dynasty, Neyshabur was the central market of jewels and turquoise in Iran. It would be far from truth if one assumes that without a scientific method of turquoise quality grading, this gem can be presented in the market. In this research, existing references of Persian historical times are analyzed from turquoise quality grading point of view and the results are compared to those of modern times. In historical Persian references, turquoise grading was done by a qualitative approach using adjectives such as better, clear, harder, fresh, good, perfect, large, whitish, yellowish white, pale and pleasing to describe the turquoise by experts. In modern times, there were some efforts to quantify the method from which the turquoise quality index (TQI) can be mentioned. However, it provides a semi-qualitative method in which different experts can rank one specimen in different classes. By analyzing Persian historical references, it can be concluded that the turquoise grading factors which are used in the modern times such as color, hardness, clarity, matrix, size, color transitions, cut, weight, enhancement, composition and availability were actually used in historical times. The only difference is trying to quantify the procedure that has resulted in modern semi-qualitative method, using turquoise quality index (TQI).
Keywords : Grading, Turquoise, Persian historical times, Modern times.
Introduction
The turquoise was extracted in Iran since fifth millennium BCE (Garazhian and Lotfi Gharaei, 2014a) and turquoise beads are found during archaeological expeditions at Ali-Kosh area, SW Iran (Hole et al., 1969) that are too far from the nowadays mines. Most probably they are transported within ancient trading networks (Garazhian and Lotfi Gharaei, 2014b). In fifth and sixth centuries A.H., Seljuk dynasty, Neyshabur was the central market of jewels and turquoise in Iran (Rahmati et al., 2013). It would be too far from truth if one assumes that without a scientific method of turquoise quality grading, this gemstone can be presented in the market. In the present research, existing references of Persian historical times are analyzed from turquoise quality grading point of view and the results are compared to those of modern times.
Methodes
The present research is performed by the use of existing references and secondary research method in which related researches including books, papers, itineraries, websites and other available references are studied in details and some notes are collected. Afterwards, by analyzing the notes, they are sorted and investigated. As a result, turquoise grading methods of Persian historical times are firstly presented and then the modern methods are depicted. Finally, the two groups of methods will be compared.
Turquoise grading at Persian historical times
Turquoise was investigated by several persons in historical Persian references. In this part, the methods of describing and grading of turquoise in Persian historical references are briefly presented, in order of date of publishing.
According to Biruni (1048 CE), by placing within the water turquoise color will be improved while being in bathroom will destroy its color.
The two colored turquoise is named “Abrash” (Johari Neyshaburi, 1195 CE). The color of turquoise will change scarcely if the structure of gemstone is hard enough; oil, strong odors and bathroom will harm the turquoise unless being hard in structure (Johari Neyshaburi, 1195 CE).
Johari Neyshabouri (1195 CE) has named Abdoli (green in color), Kuh-e Asban (green in color), Abdolmajidi (Colorful), Azhari and Ganjineh (green and blue but the color is not constant unless being hard in structure) mines in Neyshabur surroundings and has mentioned that “when enough turquoise is collected at Neyshabur mine, the gemstones are transported to the city where professionals will wet the stone by water to recognize its quality. Turquoise is merged with the host rock and cannot be graded without using water”. He has mentioned that “each mine where turquoise is extracted has a name and gemologists will immediately recognize the origin of the gemstone by experience. Afterwards, it will be graded”. On other parts of his book it has been noted that “those turquoise pieces that lose their color, in case of being large in size, will be cut to reach the parts of constant color. Other small pieces are cut, polished (by turquoise powder) and dried in front of the sun. This process will be repeated several times to obtain suitable luster. Of course all turquoise samples are not improvable”. According to Johari Neyshabouri (1195 CE), the loose white turquoise pieces are put into the organic oil. Though, in this way the color of turquoise changes to a high quality one, after several days the color will change to green. Such samples are called turquoise simulations that are not valuable. Other turquoise simulation is a white rock that is crashed by teeth very easily (most probably the rock is of gypsum and/or anhydrite composition). The white rock is washed by water and remaining part is rubbed on the willow wood and turquoise, respectively. After several days of resting, it is cut and the result is similar to turquoise (Johari Neyshaburi, 1195 CE).
Johari Neyshaburi (1195 CE) has mentioned that the cut types of turquoise are similar to those of ruby and are selected based on the shape of the sample. The cut types are named quadratic, circular, conical, octagonal, hexagonal and two other types that their upper side is bigger in dimension of which the first one is cabochon and the other one (higher and more sharp at the top) is named arrowy. In the Khorasan area, the first group of the cuts is popular while in the India, two last types are preferred.
The price of a turquoise piece is determined based on the color quality and size. There is no defined process of pricing a piece (Johari Neyshaburi, 1195 CE).
Tousi (13th CE) and Mansour (15th CE) believe that only the turquoise pieces of Neyshabur area are of good quality and they have categorized the Neyshabur turquoise in seven groups of which the first group and best one is Abu-Eshaghi (high quality in color and the best known mine); the second group is named Azhari (similar to Abu-Eshaghi and is of good quality); the third group is milky in color and is called Soleimani; the fourth group is named Zarhouni which is categorized by yellow spots on the sample and is not good in quality; the fifth group is of sky blue color and is called Khaki; the sixth group is named Abdolmajidi (Mansour, 15th CE) which is of high quality and is found in large pieces; Tousi (13th CE) just name this group as Kaftari and did not add any description; the seventh group is called Andalibi and its color resembles the color of garlic (Mansour, 15th CE) or is yellowish white in color (Tousi, 13th CE). The last group is the worst in terms of quality. Johari Neyshaburi (1195 CE) believe that Zarhouni type is colorful but cannot be compared to Abu-Eshaghi.
There are lots of turquoise mines of which the Neyshabur is the best. Turquoise also can be found in Kerman area that cannot be compared to Neyshabur (Mostofi, 1339 CE).
Mansour (15th CE) has divided turquoise into two groups, old and new. The old one has constant color and its color does not change while the new one loses its color gradually. He mentions that “the turquoise, after being extracted, is polished by rocks and the result will be used for rings or to make Tormalah. Afterwards, it is polished by willow wood or a soft rock”. Johari Neyshaburi (1195 CE) describes the Tormalah as a rock which is a combination of turquoise and host rock. The host rock will be colored in black by pencil or similar substances. It is bought in Turkistan very well”.
One of the most important Persian historical references where Neyshabur mines are described is Schlinder’s report published by Streeter (1892). He has mentioned that the Turquoises of the Ali Mirzai mine are not good, as their color soon fades. “On the top of the Reish mine, in the same valley, a vein of turquoises was discovered a few years ago, and a new mine was opened there with the name of “Sar-i-Reish” (the head of the Reish). In it are found turquoises of fine color and great size, but the color soon fades and the turquoise becomes a dirty green with white and grey spots. As long as these turquoises are kept damp they preserve their color, but if once they get dry they are worth very little. A turquoise as large as a walnut and of a fine color was found in this mine in 1882, and was presented to the Shah; but, after it had been two days with His Majesty, it became green and whitish, and was found to be worth nothing” (Streeter, 1892). “The next and last, also the most westerly valley, is the one with the Kemeri mine. This mine, which is full of water, has some thick veins of turquoises, but the stones are of no use for rings, being generally worked into amulets, brooches and seals” (Streeter, 1892).
It seems that at least up to eighteen and nineteen centuries, the data on Persian turquoise is generally achieved from Iranian references (Ovissi et al., 2016). The finest turquoises are obtained from Khaki mines. In fact, good ring stones are seldom produced by the rock mines (Pogue, 1915). The turquoises are divided at the mines into three classes: (1) Angushtari, (2) Barkhaneh, and (3) Arabi (Streeter, 1892; Pogue, 1915).
All stones of pleasing, permanent color and favorable shape are called Angushtari, meaning ring stones, and are sold by the piece. No two stones are alike, and each turquoise requires individual consideration of its special properties before appraisal. A stone two-thirds by two-fifths by one-half inch in dimensions, cut “peikani” (conical), was valued at Meshed at $1,500; another of about the same size, shape, and cut was valued at only $400. Turquoises of the size of a pea bring as much as $40. The most valued color is deep sky-blue; the slightest imperfection, or an almost inappreciable tinge of green, decreases the value considerably. A deep indigo-blue, called “talkh,” or bitter, also lessens the value. A good stone, in short, must possess an indefinable property called the “zat” which is something like the “water” of a diamond or the luster of a pearl; a fine-colored turquoise without the “zat” is not of much worth. The best ring stones are found in the Khaki diggings and in the Abdurrezzagi mine (Pogue, 1915).
Stones of intermediate quality are called Barkhaneh, and are divided into four grades. They are sold by weight; the first grade brings at the mines $450 per pound, the fourth grade only about $22 to $25 per pound. At Meshed one can buy small cut stones of the third grade for about 75 cents per thousand. Only the first grade and part of the second, are sent to Europe; the others are sold to Persian artisans, chiefly at Meshed, who use them for inlaying and incrusting jewelry, arms, trappings, etc. European jewelers use many of the best Barkhaneh stones for rings, but the fact that they are not classed at the mines as ring stones shows that they are not of the finest quality (Pogue, 1915).
All stones not belonging to the first two kinds are called Arabi. The name originated from the ready sale, on one occasion, of a great quantity of inferior stones to the Arabs. Since then any pale-colored, greenish, or spotted turquoise is called Arabi. The whitish stones of this kind are termed shirbumi or shirfam; the round pieces with white crust, chaghaleh. A few of the Arabi stones reach Europe. The large flat pieces and slabs used for amulets, bracelets, etc., at the mines called tufal; are now classed with the Arabi stones, though some are very much esteemed; pieces two by one by one-eighth inches being sometimes valued at $16. Twelve pounds of pale, uncut tufal stones on one occasion brought $300. Stones of a greenish color, called Gul-i-Kasni (chicory) are bought principally by Afghans (Pogue, 1915).
Turquoise Grading in Modern Times
Nowadays, gemologists try to find a quantitative way to grade the gemstones and improve the quality of gemstones evaluations. As a result, Fan and Yong (2005) have introduced a method to quantify the turquoise grading. They have graded 14 turquoise samples according to color, pattern, texture and cut. Compared to the samples’ marketing prices, the result of the turquoise samples given by quantitative-analysis is corresponding. The turquoise always appears as aggregation and its color, texture and transparency are different from high-class to inferior-class. So, the quantitative-analysis about the turquoise has some limits (Fan and Yong, 2005).
Typically, whether a fashioned turquoise meets the ideal or departs from it, it’s judged on three basic qualities; its color, its texture, and the presence or absence of matrix. The most-prized turquoise color is an even, intense, medium blue and the most valuable turquoise is of no matrix and the ability to take a good polish. Turquoise is most often fashioned as a cabochon. The smoothly rounded dome shape sets off turquoise’s color, texture, and any matrix beautifully. Turquoise can be found in different sizes but for any size, the quality and evenness of the color is the overriding value factor (Gemological Institute of America, 2016).
The Turquoise Skies Inc. (2016) has developed a semi-quantitative method of turquoise grading. The total price is obtained by the multiplication of weight (carat) to TQI (Turquoise Quality Index). TQI is a measurement of the quality of the turquoise stone. The TQI is a number on a scale between 8 and 100. The higher the TQI number means the better quality the turquoise, the higher the grade and the more valuable the stone. High numbers are rare; less that 1% of turquoise on the market score a 90 or better.
For achieving the TQI, eight factors including hardness, enhancement, composition, cut, availability, color, matrix and size are measured. Table 2 shows the procedure of scoring. Finally, the total scores will be checked by the table 1 and the price of each carat will be determined. It’s noteworthy that by increasing the weight, the price will be increased.
Table 2- Indicators for measuring the TQI (Turquoise Skies Inc., 2016).

Hardness plastic chalk reconstituted Below 5 on MOHS scale pro stabilization +5 on MOHS scale high natural hardness +5 on MOHS scale
1 to 20 1 3 5 10 15 20
Enhancement plastic reconstituted heavy stabilization/dyed pro stabilization waxed/oiled / Zachary process natural Chalk
1 to 20 1 2-5 6-12 13-19 20 5
Composition plastic reconstituted/
chalk required stabilization or unstable host rock/ high calcite and quartz in matrix stabilization and minor imperfections in matrix pro stabilization
pure natural turquoise/ solid matrix rare elements in matrix
1 to 10 1 2-3 4-5 6-7 8-9 10
Cut raw rolled or cut standard machine cab hand shaped cab hand sculpted design
1 to 5 1 2 3 4 5
Availability synthetic chalk or reconstituted common mine uncommon mine rare hat mine or rare specimens extremely rare
1 to 20 1 2-5 6-12 13-17 18-19 20
Color synthetic artificially dyed dull, cloudy/harsh transitions limited expression of color, imperfections in color transitions Rich color, smooth color transitions Rich color, smooth color transitions
1 to 20 1 2 3-5 6-7 8-9 10
Matrix synthetic artificially dyed no pattern, Cloudy clarity common pattern, grainy clarity rare patterns,
flawless clarity rare patterns, flawless clarity
1 to 20 1 2 3-5 6-7 8-9 10
Contiguous size smaller than 1/4″ 1/4″ to 1″ 1″ to 2″ 2″ to 4″ +4″
1 to 5 1 2 3 4 5

In the Persian historical references, turquoise grading is described as a qualitative method in which some adjectives such as better, clear, harder, fresh, good, perfect, large, whitish, yellowish white, pale and pleasing are used. The grading processes were done by experts. The price of each piece was determined based on the experiments and in some periods of time, some pricing factors were changed. According to Johari Neyshaburi (1195 CE), no particular rule were defined for pricing the turquoise pieces. In the modern times, researchers have tried to define a quantitative method of turquoise grading of which Turquoise Quality Index (TQI) can be named (Turquoise Skies Inc., 2016). Anyway, this method is a semi-quantitative method by which several persons can score a particular piece in different manners.
On the other hand, by studying the Persian historical references it can be concluded that the modern effective indicators such as color, hardness, clarity, matrix, size, color transitions, cut, weight, enhancement, composition and availability were actually used in the past. The only difference is trying to quantify the procedures that has resulted in the modern semi-quantitative methods.

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