Histoire d'alimenter les histoires minéralogiques de coin du feu...
À noter que je ne m'arrêterai pas sur des questions sémantiques de type : qu'est-ce qu'une pierre précieuse ? semi-précieuse ? Tolkien parle tout en même temps de gemmes, de perles, de roches (jade, porphyre...) et je suivrai son usage. L'important est la symbolique commune que tous ces (riches) choses partagent.

1. Quelles pierres trouve-t-on en Terre du Milieu ?

On y trouve, tout à trac, des diamants, des perles, du cristal, des émeraudes, des saphirs, des grenats, des rubis, des topazes, de l'ambre, des chrysoprases, des améthystes, des béryls, des pierres de lune, de l'onyx, du porphyre, des agates, des opales, du jade, "et bien d'autres pierres moindres", le tout en quantité.

Ci-dessous est un relevé de sources non exhaustif, mais où je me suis attaché à reprendre tout ce qui m'a paru significatif. Il manque donc la plupart des citations purement symboliques (de type "la lune brillait comme un diamant") et les HoME les plus obscurs quand j'avais déjà pléthore de citations. Quand j'en manquais... j'ai creusé davantage. :-)

Je commenterai l'importance relative des pierres ultérieurement.

a. Généralités

But those of the Noldoli whom Aule had most deeply taught laboured in secret unceasingly, and of Aule they had wealth of metals and of stones and marbles, and of the leave of the Valar much store too was granted to them of the radiance of Kulullin and of Telimpe held in hidden bowls. Starlight they had of Varda and strands of the bluest ilwe Manwe gave them; water of the most limpid pools in that creek of Kor, and crystal drops from all the sparkling founts in the courts of Valmar. Dews did they gather in the woods of Orome, and flower-petals of all hues and honeys in Yavanna's gardens, and they chased the-beams of Laurelin and Silpion amongst the leaves. But when all this wealth of fair and radiant things was gathered, they got of the Solosimpi many shells white and pink, and purest foam, and lastly some few pearls.

These pearls were their model, and the lore of Aule and the magic of the Valar were their tools, and all the most lovely things of the substance of the Earth the matters of their craft – and therefrom did the Noldoli with great labour invent and fashion the first gems. Crystals did they make of the waters of the springs shot with the lights of Silpion; amber and chrysoprase and topaz glowed beneath their hands, and garnets and rubies they wrought, making their glassy substance as Aule had taught them but dyeing them with the juices of roses and red flowers, and to each they gave a heart of fire. Emeralds some made of the water of the creek of Kor and glints among the grassy glades of Valinor, and sapphires did they fashion in great profusion, [?tingeing] them with the airs of Manwe; amethysts there were and moonstones, beryls and onyx, agates of blended marbles and many lesser stones, and their hearts were very glad, nor were they content with a few, but made them jewels in immeasurable number till all the fair substances were well nigh exhausted and the great piles of those gems might not be concealed but blazed in the light like beds of brilliant flowers. Then took they those pearls that had and some of wellnigh all their jewels and made a new gem of a milky pallor shot with gleams like echoes of all other stones, and this they thought very fair, and they were opals; but still some laboured on, and of starlight and the purest water-drops, of the dew of Silpion, and the thinnest air, they made diamonds, and challenged any to make fairer.

Then arose Feanor of the Noldoli and fared to the Solosimpi and begged a great pearl, and he got moreover an urn full of the most luminous phosphor-light gathered of foam in dark places, and with these he came home, and he took all the other gems and did gather their glint by the light of white lamps and silver candles, and he took the sheen of pearls and the faint half-colours of opals, and he [?bathed] them in phosphorescence and the radiant dew of Silpion, and but a single tiny drop of the light of Laurelin did he let fall therein, and giving all those magic lights a body to dwell in of such perfect glass as he alone could make nor even Aule compass, so great was the slender dexterity of the fingers of Feanor, he made a jewel -- and it shone of its own......... o radiance in the uttermost dark; and he set it therein and sat a very long while and gazed at its beauty. Then he made two more, and had no more stuffs: and he fetched the others to behold his handiwork, and they were utterly amazed, and those jewels he called Silmarilli. (HoME I)

b. Diamant

So they came to the Golden Gate, the last of the ancient gates of Turgon that were wrought before the Nirnaeth; and it was much like the Gate of Silver, save that the wall was built of yellow marble, and the globes and parapet were of red gold; and there were six globes, and in the midst upon a golden pyramid was set an image of Laurelin, the Tree of the Sun, with flowers wrought of topaz in long clusters upon chains of gold. And the Gate itself was adorned with discs of gold, many-rayed, in likenesses of the Sun, set amid devices of garnet and topaz and yellow diamonds. (UT)

But in the centre, above the midmost pillar and the greatest, was raised a mighty image of the king-helm of Turgon, the Crown of the Hidden Kingdom, set about with diamonds. (UT)

All in silver was he clad, and upon his shining helm there was set a spike of steel pointed with a diamond; and as his esquire took his shield it shimmered as if it were bedewed with drops of rain, that were indeed a thousand studs of crystal. (UT)

But the richest gift he brought for Erendis, and that was a diamond. (UT)

It is told in "Aldarion and Erendis" (p.193) that Erendis caused the diamond which Aldarion brought to her from Middle-earth "to be set as a star in a silver fillet; and at her asking he bound it on her forehead." For this reason she was known as Tar-Elestirnë, the Lady of the Star-brow; "and thus came, it is said, the manner of the Kings and Queens afterward to wear as a star a white jewel upon the brow, and they had no crown" (p. 225, note 18). This tradition cannot be unconnected with that of the Elendilmir, a star-like gem borne on the brow as a token of royalty in Arnor; but the original Elendilmir itself, since it belonged to Silmarien, was in existence in Númenor (whatever its origin may have been) before Aldarion brought Erendis' jewel from Middle-earth, and they cannot be the same. (UT)

Gandalf, Gandalf! Good gracious me! Not the wandering wizard that gave Old Took a pair of magic diamond studs that fastened themselves and never came undone till ordered? (The Hobbit)

What magnificence to possess a waistcoat of fine diamonds! (The Hobbit)

He [Gloin] wore a silver belt, and round his neck hung a chain of silver and diamonds. (SdA)

At the far end of the house, beyond the hearth and facing north towards the doors, was a dais with three steps; and in the middle of the dais was a great gilded chair. Upon it sat a man [Theoden] so bent with age that he seemed almost a dwarf; but his white hair was long and thick and fell in great braids from beneath a thin golden circle set upon his brow. In the centre upon his forehead shone a single white diamond. (SdA)

None of Durin's race would mine those caves for stones or ore, not if diamonds and gold could be got there. (SdA)

Many jewels the Noldor gave them, opals and diamonds and pale crystals, which they strewed upon the shores and scattered in the pools; marvellous were the beaches of Elendë in those days. A nd many pearls they won for themselves from the sea, and their halls were of pearl, and of pearl were the mansions of Olwë at Alqualondë, the Haven of the Swans, lit with many lamps. (The Silmarillion)

c. Grenat

And the Gate itself was adorned with discs of gold, many-rayed, in likenesses of the Sun, set amid devices of garnet and topaz and yellow diamonds. (UT)

His [the dead warrior from Dunharrow] belt was of gold and garnets. (SdA)

Then Turgon king of Gondolin robed in white with a belt of gold, and a coronet of garnets was upon his head. (HoME II)

d. Rubis

They stood on a wet floor of polished stone, the doorstep, as it were, of a rough-hewn gate of rock opening dark behind them. But in front a thin veil of water was hung, so near that Frodo could have put an outstretched arm into it. It faced westward. The level shafts of the setting sun behind beat upon it, and the red light was broken into many flickering beams of ever-changing colour. It was as if they stood at the window of some elven-tower, curtained with threaded jewels of silver and gold, and ruby, sapphire and amethyst, all kindled with an unconsuming fire. (SdA)

Now the folk of the Swallow bore a fan of feathers on their helms, and they were arrayed in white and dark blue and in purple and black and showed an arrowhead on their shields. Their lord was Duilin, swiftest of all men to run and leap and surest of archers at a mark. But they of the Heavenly Arch being a folk of uncounted wealth were arrayed in a glory of colours, and their arms were set with jewels that flamed in the  light now over the sky. Every shield of that battalion was of the blue of the heavens and its boss a jewel built of seven gems, rubies and amethysts and sapphires, emeralds, chrysoprase, topaz, and amber, but an opal of great size was set in their helms. Egalmoth  was their chieftain, and wore a blue mantle upon which the stars  were broidered in crystal, and his sword was bent -- now none else of the Noldoli bore curved swords -- yet he trusted rather to the bow, and shot therewith further than any among that host. (HoME II)

Gimli's song  here appears  (in a  rider to  the manuscript)  written out clear in its  final form  (but with  countless lamps  for shining  lamps in the third verse, and There ruby, beryl, opal pale  for There  beryl, pearl, and opal  pale in  the fourth). (HoME VII)

e. Emeraude

The necklace of Girion, Lord of Dale, made of five hundred emeralds green as grass, which he gave for the arming of his eldest son in a coat of dwarf linked rings the like of which had never been made before, for it was wrought of pure silver to the power and strength of triple steel. (The Hobbit)

To the Elvenking he gave the emeralds of Girion, such jewels as he most loved, which Dain had restored to him. (The Hobbit)

Eärendil was a mariner
[…]
          In panoply of ancient kings,
          in chainéd rings he armoured him;
          his shining shield was scored with runes
          to ward all wounds and harm from him;
          his bow was made of dragon-horn,
          his arrows shorn of ebony,
          of silver was his habergeon,
          his scabbard of chalcedony;
          his sword of steel was valiant,
          of adamant his helmet tall,
          an eagle-plume upon his crest,
          upon his breast an emerald. (SdA)

Now the folk of the Swallow bore a fan of feathers on their helms, and they were arrayed in white and dark blue and in purple and black and showed an arrowhead on their shields. Their lord was Duilin, swiftest of all men to run and leap and surest of archers at a mark. But they of the Heavenly Arch being a folk of uncounted wealth were arrayed in a glory of colours, and their arms were set with jewels that flamed in the  light now over the sky. Every shield of that battalion was of the blue of the heavens and its boss a jewel built of seven gems, rubies and amethysts and sapphires, emeralds, chrysoprase, topaz, and amber, but an opal of great size was set in their helms. Egalmoth  was their chieftain, and wore a blue mantle upon which the stars  were broidered in crystal, and his sword was bent -- now none else of the Noldoli bore curved swords -- yet he trusted rather to the bow, and shot therewith further than any among that host. (HoME II)

f. Saphir

Upon the very Eve of Midsummer, when the sky was blue as sapphire and white stars opened in the East (SdA)
It was as if they stood at the window of some elven-tower, curtained with threaded jewels of silver and gold, and ruby, sapphire and amethyst, all kindled with an unconsuming fire. (SdA)

Now the folk of the Swallow bore a fan of feathers on their helms, and they were arrayed in white and dark blue and in purple and black and showed an arrowhead on their shields. Their lord was Duilin, swiftest of all men to run and leap and surest of archers at a mark. But they of the Heavenly Arch being a folk of uncounted wealth were arrayed in a glory of colours, and their arms were set with jewels that flamed in the  light now over the sky. Every shield of that battalion was of the blue of the heavens and its boss a jewel built of seven gems, rubies and amethysts and sapphires, emeralds, chrysoprase, topaz, and amber, but an opal of great size was set in their helms. Egalmoth  was their chieftain, and wore a blue mantle upon which the stars  were broidered in crystal, and his sword was bent -- now none else of the Noldoli bore curved swords -- yet he trusted rather to the bow, and shot therewith further than any among that host. (HoME II)

g. Topaze

So they came to the Golden Gate, the last of the ancient gates of Turgon that were wrought before the Nirnaeth; and it was much like the Gate of Silver, save that the wall was built of yellow marble, and the globes and parapet were of red gold; and there were six globes, and in the midst upon a golden pyramid was set an image of Laurelin, the Tree of the Sun, with flowers wrought of topaz in long clusters upon chains of gold. And the Gate itself was adorned with discs of gold, many-rayed, in likenesses of the Sun, set amid devices of garnet and topaz and yellow diamonds. (UT)

Now the folk of the Swallow bore a fan of feathers on their helms, and they were arrayed in white and dark blue and in purple and black and showed an arrowhead on their shields. Their lord was Duilin, swiftest of all men to run and leap and surest of archers at a mark. But they of the Heavenly Arch being a folk of uncounted wealth were arrayed in a glory of colours, and their arms were set with jewels that flamed in the  light now over the sky. Every shield of that battalion was of the blue of the heavens and its boss a jewel built of seven gems, rubies and amethysts and sapphires, emeralds, chrysoprase, topaz, and amber, but an opal of great size was set in their helms. Egalmoth  was their chieftain, and wore a blue mantle upon which the stars  were broidered in crystal, and his sword was bent -- now none else of the Noldoli bore curved swords -- yet he trusted rather to the bow, and shot therewith further than any among that host. (HoME II)

h. Chrysoprase

Now the folk of the Swallow bore a fan of feathers on their helms, and they were arrayed in white and dark blue and in purple and black and showed an arrowhead on their shields. Their lord was Duilin, swiftest of all men to run and leap and surest of archers at a mark. But they of the Heavenly Arch being a folk of uncounted wealth were arrayed in a glory of colours, and their arms were set with jewels that flamed in the  light now over the sky. Every shield of that battalion was of the blue of the heavens and its boss a jewel built of seven gems, rubies and amethysts and sapphires, emeralds, chrysoprase, topaz, and amber, but an opal of great size was set in their helms. Egalmoth  was their chieftain, and wore a blue mantle upon which the stars  were broidered in crystal, and his sword was bent -- now none else of the Noldoli bore curved swords -- yet he trusted rather to the bow, and shot therewith further than any among that host. (HoME II)

i. Beryl

He held out his hand, and showed a single pale-green jewel. 'I found it in the mud in the middle of the Bridge,' he said. 'It is a beryl, an elf-stone. Whether it was set there, or let fall by chance, I cannot say; but it brings hope to me. I will take it as a sign that we may pass the Bridge; but beyond that I dare not keep to the Road, without some clearer token.' (SdA)

There hammer on the anvil smote,
          There chisel clove, and graver wrote;
          There forged was blade, and bound was hilt;
          The delver mined, the mason built.
          There beryl, pearl, and opal pale,
          And metal wrought like fishes' mail,
          Buckler and corslet, axe and sword,
          And shining spears were laid in hoard. (SdA)

Gimli's song  here appears  (in a  rider to  the manuscript)  written out clear in its  final form  (but with  countless lamps  for shining  lamps in the third verse, and There ruby, beryl, opal pale  for There  beryl, pearl, and opal  pale in  the fourth). (HoME VII)

j. Améthyste

It was as if they stood at the window of some elven-tower, curtained with threaded jewels of silver and gold, and ruby, sapphire and amethyst, all kindled with an unconsuming fire. (SdA)
Then cried Osse: "Look, 0 Manwe, but the sea is blue, as blue wellnigh as Ilwe that thou lovest!" and "Nay," said Manwe, "envy we not Ilwe, for the sea is not blue alone, but grey and green and purple, and most beauteous-flowered with foaming white. Nor jade nor amethyst nor porphyry set with diamonds and with pearls outrival the waters of the Great and little seas when the sunlight drenches them." (HoME I)

k. Opale

There hammer on the anvil smote,
          There chisel clove, and graver wrote;
          There forged was blade, and bound was hilt;
          The delver mined, the mason built.
          There beryl, pearl, and opal pale,
          And metal wrought like fishes' mail,
          Buckler and corslet, axe and sword,
          And shining spears were laid in hoard. (SdA)

Every shield of that battalion was of the blue of the heavens and its boss a jewel built of seven gems, rubies and amethysts and sapphires, emeralds, chrysoprase, topaz, and amber, but an opal of great size was set in their helms. Egalmoth  was their chieftain, and wore a blue mantle upon which the stars  were broidered in crystal, and his sword was bent -- now none else of the Noldoli bore curved swords -- yet he trusted rather to the bow, and shot therewith further than any among that host. (HoME II)
Many jewels the Noldor gave them, opals and diamonds and pale crystals, which they strewed upon the shores and scattered in the pools; marvellous were the beaches of Elendë in those days. And many pearls they won for themselves from the sea, and their halls were of pearl, and of pearl were the mansions of Olwë at Alqualondë, the Haven of the Swans, lit with many lamps. (The Silmarillion)

l. Perle

"I beg of you," said Bilbo stammering and standing on one foot, "to accept this gift!" and he brought out a necklace of silver and pearls that Dain had given him at their parting. (The Hobbit)

With that he put on Bilbo a small coat of mail, wrought for some young elf-prince long ago. It was of silver-steel which the elves call mithril, and with it went a belt of pearls and crystals. A light helm of figured leather, strengthened beneath with hoops of steel, and studded about the bring with white gems, was set upon the hobbit's head. (The Hobbit)

'Also there is this!' said Bilbo, bringing out a parcel which seemed to be rather heavy for its size. He unwound several folds of old cloth, and held up a small shirt of mail. It was close-woven of many rings, as supple almost as linen, cold as ice, and harder than steel. It shone like moonlit silver, and was studded with white gems. With it was a belt of pearl and crystal. (SdA)

There beryl, pearl, and opal pale, (SdA)

Sam, waking suddenly by some instinct of watchfulness, saw first his master's empty bed and leapt to his feet. Then he saw two dark figures, Frodo and a man, framed against the archway, which was now filled with a pale white light. He hurried after them, past rows of men sleeping on mattresses along the wall. As he went by the cave-mouth he saw that the Curtain was now become a dazzling veil of silk and pearls and silver thread: melting icicles of moonlight. But he did not pause to admire it, and turning aside he followed his master through the narrow doorway in the wall of the cave. (SdA)

Then the guards stepped forward, and Faramir opened the casket, and he held up an ancient crown. It was shaped like the helms of the Guards of the Citadel, save that it was loftier, and it was all white, and the wings at either side were wrought of pearl and silver in the likeness of the wings of a sea-bird, for it was the emblem of kings who came over the Sea; and seven gems of adamant were set in the circlet, and upon its summit was set a single jewel the light of which went up like a flame. (SdA)
   
Bilbo laughed, and he produced out of a pocket two beautiful pipes with pearl mouth-pieces and bound with fine-wrought silver. 'Think of me when you smoke them!' he said. 'The Elves made them for me, but I don't smoke now.' (SdA)

And though the Dwarves ever demanded a price for all that they did, whether with delight or with toil, at this time they held themselves paid. For Melian taught them much that they were eager to learn, and Thingol rewarded them with many fair pearls. These Círdan gave to him, for they were got in great number in the shallow waters about the Isle of Balar; but the Naugrim had not before seen their like, and they held them dear. One there was as great as a dove's egg, and its sheen was as starlight on the foam of the sea; Nimphelos it was named, and the chieftain of the Dwarves of Belegost prized it above a mountain of wealth. (The Silmarillion)

Many jewels the Noldor gave them, opals and diamonds and pale crystals, which they strewed upon the shores and scattered in the pools; marvellous were the beaches of Elendë in those days. And many pearls they won for themselves from the sea, and their halls were of pearl, and of pearl were the mansions of Olwë at Alqualondë, the Haven of the Swans, lit with many lamps. (The Silmarillion)

Tar-Míriel the Queen, fairer than silver or ivory or pearls (The Silmarillion)

The Teleri  are the  Foam-riders, Musicians of the Shore, the Free, the Wanderers, and the Elves  of the  Sea, the Sailors,  the  Arrow-elves,  Ship-friends,  the  Lords  of  the Gulls, the  Blue  Elves,  the Pearl-gatherers,  and the  People of  Elwe. (HoME V)
The coat of  mail (which  Bilbo still  calls his 'elf-mail') is described as 'studded with pale pearls'  ('white gems',FR); cf. the original text  of The  Hobbit, before  it was  changed to introduce 'mithril': 'It was  of silvered  steel, and  ornamented with pearls' (VI.465, note 35). (HoME VII)

m. Jade

Then cried Osse: "Look, 0 Manwe, but the sea is blue, as blue wellnigh as Ilwe that thou lovest!" and "Nay," said Manwe, "envy we not Ilwe, for the sea is not blue alone, but grey and green and purple, and most beauteous-flowered with foaming white. Nor jade nor amethyst nor porphyry set with diamonds and with pearls outrival the waters of the Great and little seas when the sunlight drenches them." (HoME I)

n. Pas d’autre occurrence exploitable

Agate
Amber
Moonstone
Onyx

2. La taille des pierres

Les éléments ci-dessous sont principalement repris du livre d'A.-F. Cannella : "Gemmes, verre coloré, fausses pierres précieuses au Moyen-Âge"

Les pierres dures sont : le rubis, l'escarboucle, le saphir ou l'hyacinthe.
Les pierres tendres sont : la topaze, la sardoine, l'émeraude, la turquoise, l'améthyste, la calcédoine.

La taille est essentiellement en cabochon (à fond plat), avec simple polissage de la surface bombée, pour la sertir et perdre le moins de matière possible. On recherche l'éclat, la translucidité, mais pas la brillance, le scintillement. La taille suit donc beaucoup la forme naturelle de la pierre. Beaucoup de fausses pierres remplissent aussi bien cet office.

La taille à facettes est connue mais simple, essentiellement des carrés ou des rectangles à grande table et quatre facettes, en tout cas toujours des formes géométriques.

Techniques de polissage : [Après avoir mis la pierre en ciment, ] "Fais une table de plomb et répands-y du silex blanc broyé comme du poivre. Tu frotteras la pierre dessus jusqu'à ce que tu effaces les aspérités." (XIIe, Eraclius)

Certains traités précisent la "table" selon la dureté de la pierre : plomb, étain, cuivre, bois, cuir, feutre (alors que l'abrasif est presque toujours le même). La table est toujours recourbée vers le haut aux deux extrémités (forme de bassin). Les bois utilisés sont aulne, poirier, tremble. Les supports "doux" servent aux pierres tendres et au second polissage des pierres dures.

L'abrasif peut être de la poudre de tuile mouillée, de la poudre de pierre ponce, souvent de la poudre d'émeri, de la poudre de grès, de la poudre de silex, etc.

Une recette détaille : sur une table de polissage d'abord on taille avec de la poudre mouillée, qu'on change à mesure qu'elle ne taille plus bien ; ensuite on égalise et aplanit sur le poudre sèche ; enfin on éclaircit avec de la lavure (la poudre mouillée usagée de la première étape, "potée si usée qui plus ne taille"). À noter qu'il faut toujours utiliser la potée de rubis séchée pour le rubis, etc., car chacune convient à polir son semblant. "Voici la manière de tailler, former et aplanir toute pierre précieuse."

Une pierre grande sera d'abord sciée, généralement la première entaille est faite au diamant, la scie est une lame sans dent, en plomb ou en cuivre, montée sur une monture de fer, qui frotte sur de la poudre d'émeri.

On peut perforer des pierres pour les fixer sur des bijoux ou des vêtements : faire un petit trou avec un marteau et un stylet de plomb, puis mettre de la poudre d'émeri dans l'entaille et limer pour percer.

On peut encoller des pierres : mélanger du blanc d'oeuf (ou de la colle arabique) avec de la chaux vive. Quand la chaux est fraîche, le blanc d'oeuf doit être rance, et quand la chaux est rance, le blanc d'oeuf doit être frais.

Les fausses pierres sont souvent obtenues par teinture dans la masse du verre (azurite ou azur de cuivre pour contrefaire les saphirs, cendres de plomb brûlé additionné de fer pour contrefaire les émeraudes, oxyde de plomb seul pour obtenir du jaune, etc., le tout mélangé à du cristal de roche en poudre). Toutefois la coloration du verre par bain tinctorial existe aussi : réduire le verre ou le cristal en poudre, détremper cette poudre dans du blanc d'oeuf cru, mettre la préparation dans une masse de la couleur voulue et cuire. La masse est constituée de vinaigre, de sel ammoniaque, de cinabre. Avec du vert-de-gris pour obtenir une émeraude verte, de l'azur (de cuivre ou de lapis-lazuli) pour obtenir un saphir bleu, etc.

Les faussaires pratiquent également le doublet : coller une vraie pierre précieuse sur une base en fausse pierre précieuse pour en augmenter la grosseur ; dissimuler la ligne de jonction par la monture en métal.

Pour augmenter la valeur d'une pierre, le marchand la place sur une feuille d'or (ou de vermeil) pour en augmenter les feux.

Techniques pour reconnaître une vraie pierre d'une fausse (cf. article de Colette Sirat sur les traités juifs italiens d'artisans joailliers) :
1) Le feu : "Prends un morceau de cuivre rond et épais d'un demi-doigt ou moins, chauffe-le au feu jusqu'à ce qu'il rougisse, place la pierre dessus et laisse-la le temps de parcourir une rue de moyenne importance. Si elle ne devient pas noire elle est bonne. Si elle noircit enlève-la immédiatement, de peur qu'elle ne se brise."
2) Le souffle : "Si tu souffles dessus, l'humidité s'en va en un instant tandis qu'elle demeure sur le verre." [car le verre est à température ambiante et la pierre précieuse plus froide]
3) L'éloignement : "Son éclat se distingue mieux lorsqu’on se place loin."

À noter qu'avant le XVème siècle le diamant n'est qu'exceptionnellement utilisé en pierre d'ornement. Les éclats de diamants servent avant tout à tailler d'autres pierres (intailles, perforations de perles en pierre dure, etc.). Il n'en va pas de même chez Tolkien (cf. relevé de sources).