Does Turquoise Change Color?

Writing in 1915, Pogue reported:

“Much turquois fades to an unsightly grayish color or takes on a greenish cast soon after it is mined. This tendency varies greatly with different localities; the Nishapur stones, for instance, are noted for their permanency of color, while those from Sinai have a bad reputation for fading.”
— Pogue (1915), p. 24

Pogue (1915) added a practical rule:

“A stone that holds its color for a reasonable period is very likely to retain it permanently if carefully treated.”
— Pogue (1915), p. 24

On the cause, Pogue (1915) was cautious:

“The cause of the alteration in color is not clearly understood. The change is probably a chemical one, and has been attributed to the gradual drying out of the water contained (spontaneous dehydration)”
— Pogue (1915), p. 24

In a note, Pogue (1915) observed:

“Heating and usually exposure to weather causes blue turquois to turn green.”
— Pogue (1915), p. 24

According to Pogue (1915, p. 72), Muhammed Ibn Mansur's treatise of about 1300 already sorted turquoise into old and new stones: the old kept their luster and color, while the new soon lost theirs.

The same treatise, in Pogue's 1915 translation, noted how fats and odors act on the stone:

“Moisture, oil, and strong odors impair the luster of the stone; mutton fat strengthens its color, therefore on the hands of butchers are turquoises always beautifully colored.”
— Pogue (1915), p. 72

A later Persian compilation quoted by Pogue (1915) warned that

“The real blue turquois of Nishapur changes its color when kept near musk or camphor, also from the dampness of the ground, as well as from exposure to the fire”
— Pogue (1915), p. 72

Color change is behind one of the oldest turquoise beliefs. Writing in 1915, Pogue recorded the historical European belief:

“The turquois was believed to indicate the state of the wearer’s health; turning pale when he sickened, losing its color when he died, and regaining its former beauty in the hands of a new and healthy owner.”
— Pogue (1915), p. 116

Pogue (1915) explained where that belief came from:

“Its tendency to alter in color and even to fade completely to an unseemly white, coupled with notions brought with it from the Orient, were sufficient to suggest to the credulous minds of the time a more than natural power of independent action.”
— Pogue (1915), p. 115

Even in the early 1600s, as Pogue (1915) quoted him, the gem writer Boetius de Boot offered a natural explanation close to the one on this page:

“The change of color also takes place in a natural manner. Because this precious stone is not perfectly hard, it can easily assume a fine, pale, or ugly color by absorbing the vapors and exhalations that perpetually transpire from the pores of the skin.”
— Pogue (1915), p. 120

De Boot, as Pogue (1915) quoted him, also recorded an early way of improving the color:

“It is known by experience that the color of the turquois is amended by vinegar and sal ammonia, in which the sweat and exhalations of the body abound.”
— Pogue (1915), p. 120

Writing in 1915, Pogue cautioned:

“The turquois, in common with the pearl and the opal, requires constant care on the part of the wearer in order that its beauty may not be impaired. Its comparative softness and its tendency to change in color afford ample opportunity for its delicate tint to be marred or even entirely destroyed by carelessness.”
— Pogue (1915), p. 133

Pogue (1915) went on:

“Moreover, it should never be permitted to come in contact with perspiration, 6 soap lather, or with strong gases, and even perfumes are said to have a harmful effect.”
— Pogue (1915), p. 133

His practical advice in 1915:

“One should be particular to remove turquois rings before washing the hands.”
— Pogue (1915), p. 133

In a 1915 footnote, Pogue passed along one explanation then offered for fading:

“Hydrogen sulphide in small quantity is said to give blue turquois a greenish cast, and the presence of this compound in exhalations from the skin has been suggested as the cause of fading of stones when worn.”
— Pogue (1915), p. 133

Pogue (1915) also recorded how American mining companies had answered buyers' fears of color change:

“A number of American turquois companies have in the past marked their best-grade stones and guaranteed them to retain their color. The designations are “A” (American Turquois Co.), circle (Azure Turquois Co.), cross (American Turquois & Copper Co.), “T” (Toltec Turquois Co.), and arrow (Himalaya Turquois Co.).”
— Pogue (1915), p. 131

Pogue (1915, p. 37) relates that a walnut-sized stone of fine color from the Sar-i-Reish mine near Nishapur, presented to the Shah of Persia in 1881, faded and became valueless within two days.

Of that same Persian mine, Pogue (1915) wrote:

“Turquoises were obtained of fine color and large size, which preserved their color while damp, but upon drying assumed a dirty-green shade with white and gray spots.”
— Pogue (1915), p. 37

Pogue (1915) recorded how dealers hid the problem:

“Many stones were sent to Europe and kept moist in earthenware pots till sold, but when exposed to the air they lost color and in a year or two became quite white.”
— Pogue (1915), p. 38

Of the old Kerman deposits in Persia, Pogue (1915) wrote:

“The stones have a greenish color, are prone to fade, and consequently are little esteemed.”
— Pogue (1915), p. 40

Colour stability sold stones even then. Of New Mexico's Azure mine, Pogue (1915) reported:

“The cut gems of good quality are marked on the under side with a circle and guaranteed to retain their color.”
— Pogue (1915), p. 56

According to Branson (1975, p. 2), lighter-colored stones usually tended to be softer and more porous, and those were the ones that changed color with wear, while hard, dense stones did not absorb oil and grease.

Branson (1975) photographed bracelets whose stones had started out alike:

“The porous ones were darkened by wear and natural oils. The harder non-porous stones remained unchanged.”
— Branson (1975), p. 6

According to Branson (1975, p. 6), a pair of old earrings that began all blue turned green in the middle because they were cut from nuggets with soft, porous centers that absorbed skin oils over years of wear.

According to Branson (1975, p. 43), the soft blue Cerrillos turquoise of New Mexico turns green over time, sometimes to very pleasing shades, when exposed to skin oils.

According to Lowry (2010, p. 178), oil-based polishes can break down with wear, heat or light, and stones finished that way can slowly turn whitish or green as other substances attach to the surface. ^[3]

Of Zuni-style inlay and petit point polished with oil, which can shift to a duller blue or green, Lowry (2010) writes:

“This color change does not necessarily detract from the value of these styles of jewelry.”
— Lowry (2010), p. 178 ^[3]

According to Lowry (2010, p. 179), recently mined rough with a high copper content can slowly oxidize in air, so old collections of rough may hide good color under a green or rust-colored skin. ^[3]

Writing in 1913 about Tibetan heirloom stones, Laufer observed:

“There are, doubtless, also many ancient turquoises still in their possession as they are inherited from mother to daughter for generations, and thus kept as heirlooms in the same family for centuries; being constantly exposed to the open air, they readily change color and often assume a pale green shade, more or less tainted with black spots.”
— Laufer (1913), p. 5 ^[4]

Writing in 1890, Kunz said of Egyptian turquoise:

“Large quantities are brought from Egypt, but this variety, although dark-blue when found, often changes in a short time to a verdigris green.”
— Kunz (1890), p. 54 ^[5]

According to Kunz (1890, p. 59), a few stones cut from New Mexico turquoise with a very good color at the time of cutting turned the characteristic green within a few days. ^[5]

Kunz (1890) on everyday wear:

“Ammonia does not affect the color of true Persian turquoises, although washing the hands with them on usually does.”
— Kunz (1890), p. 59 ^[5]

As of 1890, Kunz still hoped depth would help:

“It is possible, that deeper workings will develop finer stones, perhaps of such material as will maintain a more permanent color.”
— Kunz (1890), p. 57 ^[5]

According to Schiffer (2008, p. 15), because turquoise is a porous stone it appears darker when wet and lighter as it dries out. ^[6]

According to Ryan & Chambless (2020, p. 278), turquoise forms in water and holds moisture between its molecules; once mined, the water dries out and the colour lightens, which is why dealers often spray water on rough turquoise when showing it to a buyer. ^[7]

According to Ryan & Chambless (2020, p. 279), every turquoise treatment, whether surface oil or wax, polymer stabilization or silica enhancement, does the same job: applied to the rough, it replaces the water with another substance to harden the stone, deepen the colour, or both. ^[7]

Ryan & Chambless (2020) on why treated stone holds its colour:

“When the hardness is increased, this treated turquoise resists color change and can be cut for use in jewelry.”
— Ryan & Chambless (2020), p. 278 ^[7]

Richard M. Shull, in an appendix to Ryan & Chambless (2020, p. 339), wrote that turquoise is usually somewhat porous and can absorb moisture, skin oils, hand creams and perfumes that change its colour. Only the small share of gem-grade turquoise holds its colour over time, which is why so much turquoise sold today has been treated or enhanced. ^[7]

Khazeni (2014) on the stone's colour:

“But the color is inconstant and unstable and can fade to green. It is in the nature of turquoise to change.”
— Khazeni (2014), p. 18 ^[8]

According to Khazeni (2014, p. 25), medieval authors such as al-Biruni attributed turquoise's changes of colour to atmosphere and climate: cloudy skies, winds and sun. ^[8]

Khazeni (2014) records the jewellers' term for a faded stone:

“When a stone lost its color, it lost its worth as well, being known in the language of jewelers as a dead stone (sang-i murda), although it could be brought back to life through contact with water and sun.”
— Khazeni (2014), p. 25 ^[8]

According to Khazeni (2014, p. 36), Ibn Mansur's Javahirnama held that the colour of turquoise was set by when it was taken from the mine: stones from the old mines had already finished changing, while those of the new mines were still changing their hue, so the large, lustrous blue stones found in the newer mines soon faded to green. ^[8]

Chardin, as Khazeni (2014) quotes him, on the second Persian mine of his day:

“They call them the new rock to distinguish them from the others which are old: the color of it goes off in time.”
— Khazeni (2014), p. 78 ^[8]

Thomas Nichols's English lapidary of 1652, as Khazeni (2014) quotes it:

“Some of the Orientall ones are said to keep their colour perpetually, and those are called Turkies of the old rock”
— Khazeni (2014), p. 85 ^[8]

According to Khazeni (2014, p. 85), de Boot recorded that jewelers had devised ways to restore the colour of faded turquoise: some soaked the stones in water of chrysocolla mixed with ultramarine pigment (made from lapis lazuli), while others sanded them with emery and polished them with tripoli until the unoxidized layer beneath showed through. ^[8]

According to Khazeni (2014, p. 123), Houtum-Schindler reported in the 1880s that fast-fading stones from new-rock mines such as Ghar-i Raʾis, dug to replace the older mines, were circulating worldwide and had devalued Persian turquoise. ^[8]

According to Khazeni (2014, p. 123), as new-rock stones flooded the market, turquoise came to be seen by some as merely semiprecious, even 'the most treacherous of all precious stones'. ^[8]

Khazeni (2014) records the European belief that a gifted turquoise reflected the giver's affection,

“this stone being as liable to change and caprice as the human heart itself.”
— Khazeni (2014), p. 123 ^[8]

Lowry (2002) on why some stones change:

“Low-grade turquoise, which is more common, is soft and porous so it easily absorbs creams and body oils and tends to dry out when exposed to sunlight or extreme heat.”
— Lowry (2002), p. 2 ^[9]

Lowry (2002) on the harder grades:

“Harder, gemstone-grade turquoise stones, which are rarer, are impervious to body oils and their color remains consistent over time.”
— Lowry (2002), p. 3 ^[9]

Lund (1976) on which stones change:

“All turquoise does not change color with age. Only those stones which are less than top grade or gem quality, which are more porous and therefore more susceptible to body oils, alter their color with age.”
— Lund (1976), p. 142 ^[10]

Lund (1976, p. 142) told buyers that mismatched blue and green stones in an old piece were not careless matching: the stones had matched when set, and over the years the more porous ones absorbed more body oil and darkened. ^[10]