Part 5

Some crystals contain in their substance drops of water, or other kind of fluid; and these, as curiosities, are usually sold at a rate considerably higher than others. There are in the British Museum specimens of crystal which enclose many kinds of foreign substances, such as ironstone, needle antimony, and asbestos (136).

Various means have been devised for communicating colours to rock crystal. If it be heated and plunged into a solution of indigo, or copper, it acquires a blue colour; or if into a decoction of cochineal, a red colour. A clove─brown colour may be given by exposing it to the vapour of burning wood. Artists sometimes communicate beautiful colours to rock crystals, by forming them into what are called _doublets_. Two modes of doing this are adopted. In one, a stone that is brilliant─cut at the top is hollowed underneath, filled with the colour that the stone is intended to exhibit, and then closed at the bottom by a plate of glass. If this kind of doublet be dexterously executed, the deception is not easily discovered; for the whole mass will appear of an uniform tint. The second kind of doublet is formed by cementing a coloured plate of glass on the base of a rose or brilliant─cut crystal: by this the whole stone acquires the colour of the plate.

There are found in nature, many coloured kinds of crystal. These are often confounded with precious stones; and, as such, are made into female ornaments of different kinds. The following are the principal of them.

79. COMMON AMETHYST.—_This is a violet─coloured crystal_, which acquires considerable brilliancy in polishing, and is sometimes of sufficient size to be formed into columns more than a foot in height, and several inches in diameter. When the colour is good, and uniformly diffused, amethysts are cut into necklaces, bracelets, ear─rings, and seals; and, when less pure, they are manufactured into snuff─boxes. They are valued in proportion to the depth of their colour, and to their perfect transparency. The most favourite form in which they are made up is in necklaces; and as it is not easy to find a number of perfect stones with precisely the same tint of colour, necklaces of this description are very valuable. The finest that is known was in the possession of her late Majesty. When the colour is not uniformly diffused, jewellers sometimes expose amethysts, for a little while, in a mixture of sand and iron─filings, to a moderate heat; and, by this process, their appearance is rendered more uniform.

The amethyst being almost the only coloured stone that can be worn with mourning, it derives, from this circumstance, a considerable addition of value.

This species of gem was well known to the ancient Greeks and Romans, and was held by them in great esteem. Its name is derived from the Greek language, and implies a power of preventing intoxication; which (originating no doubt in the resemblance of its colour to that of wine, and the absurd doctrine of sympathies) it was believed by the ancients to possess. They ascribed to it many other virtues, equally surprising and equally absurd; particularly that the wearing of it would expel melancholy, procure the confidence and friendship of princes, render people happy, and even dispel storms of wind and hail. The ancients frequently engraved upon amethyst; and their favourite subject was the representation of Bacchus and his followers.

The most valuable amethysts are imported into Europe from India and Ceylon. These, although they are with truth denominated oriental, must be carefully distinguished from the true oriental amethyst (55), which is a much more valuable gem. The amethysts next in esteem are found in Brazil, and are procured in the mining districts of that country. Siberia, and various countries in Europe, especially Germany and Spain, also furnish very beautiful amethysts; and inferior stones of this description are even found in the mountainous districts of some parts both of Scotland and Ireland.

80. FALSE RUBY _is a crystal of red colour_, and found in Bohemia, Silesia, and Barbary.

81. FALSE, _or_ WATER SAPPHIRE _is a blue crystal_, which does not differ much in appearance from the true sapphire, but is considerably less hard. This kind is found in Bohemia, Silesia, and some parts of Switzerland, but it is not so valuable as the last.

82. FALSE EMERALD _is a green variety of crystal_, the scarcest and most valuable of all the coloured kinds. It is chiefly found in Saxony and Dauphiny.

83. YELLOW, _or_ TOPAZINE CRYSTAL _is a stone of wine─yellow colour_. It is found in Brazil and Bohemia, but has no other alliance with the true topaz than its colour.

84. CAIRN GORUM CRYSTALS are obtained in various parts of Scotland, but particularly from a mountain of that name in the county of Aberdeen. _They are usually of smoky yellow or brown colour_, and are, at this time, so much in request for ornamental articles of dress, that several lapidaries have been induced to settle in Aberdeen, who are constantly employed in cutting them for seals, rings, necklaces, brooches, and other trinkets. When these crystals are of deep and good colour, they are nearly as estimable as topazes; and, if clear and large, they are sold at a high rate. The price of inferior seal─stones varies from ten shillings to three or four pounds each; but those of superior beauty will produce from five to ten guineas. Such specimens as have a pure and full yellow colour are often sold for topazes. When they are muddy, the lapidaries have the art of entirely dissipating the colour, and giving them a transparent lustre. This is done by means of heat, which will dissipate the colour of every species of crystal.

85. _AVANTURINE is a quartz, generally of reddish colour, sprinkled with yellowish shining points of mica (123), which are dispersed through its whole substance._

A French artist, some years ago, having by accident, or “par aventure,” suffered a quantity of brass filings to fall into a vessel of melted glass, afterwards found that it was admirably calculated for vases and different kinds of ornamental work. Hence he denominated it avanturine, a name which mineralogists have since applied to those natural objects of which this production of art was an apparent imitation.

Avanturine is found in some of the countries bordering upon the White Sea, in Spain, and some parts of France. In the late Leverian Museum there was a piece which weighed near five pounds, and was unique both for beauty and magnitude. It had been discovered in 1788, amongst the ruins of the triumphal arch of Julius Cæsar in the valley of Suse, in Piedmont; and was purchased of the person who found it for 200 guineas. Avanturine is cut into various ornamental articles, which are sometimes sold at a very high price.

Imitations of it are very common, and are formed by the simple operation of throwing brass or copper filings into coloured glass in a state of fusion.

86. _CATS─EYE is a stone of brownish grey colour, tinged with green, yellow, white, or red; semi─transparent, and reflecting from its interior a splendid white line or speck, which_ _varies according to the direction in which the stone is held to the light._

_It is found in pieces that are rounded, massive, or blunt─edged._

These stones are considered by some writers as varieties of quartz (76), and by others as a kind of opal (102). They are sometimes found in Hanover, but are chiefly brought from the island of Ceylon. It is usual to cut them before they are exported, and generally in a convex and oblong form, without facets, and in such manner as to bring the streak which intersects them into the centre. Among the king of Candy’s jewels, which were sold by auction in London, in June 1820, was a cat’s─eye of extraordinary magnitude and beauty. It was two inches in diameter, of dark colour, and nearly hemispherical. This stone was set in gold, with small rubies round it, and was sold for more than 400_l._

Cat’s─eyes are chiefly used for setting in rings. Their size seldom exceeds that of a hazel nut; but there was one in the cabinet of the Dukes of Tuscany, which was nearly an inch in diameter. Those that are the most highly esteemed are of an olive─green, or red colour.

87. _WOODSTONE is a very hard mineral substance, supposed to have been wood petrified with a siliceous mineral called hornstone._

_It is of various colours; and has not only the external appearance, but the internal organization of wood._

This extraordinary mineral is found embedded in sandy loam, in alluvial soil (269), and occurs in various parts both of Europe and Asia. It has been found in ferruginous sand, near Woburn, in Bedfordshire, and near Nutfield, in Surrey. Immense pieces of it are discovered in some places in the original shape of the trees; trunks, branches, and roots. In the year 1752 the whole under part of the trunk of a tree, with its branches and roots, was found, in a state of woodstone, near Chemnitz, in Saxony; and, in the Electoral Cabinet at Dresden, there is part of the trunk of a tree, from the same place, which measures five feet in length and as many in thickness.

Woodstone is in considerable request by lapidaries. It takes a good polish, and is made into beads for necklaces, and other female ornaments. In the East Indies it is generally called _Petrified Tamarind Tree_.

88. _COMMON SAND is a granulated kind of quartz; or consists of rounded grains of small size, which have a vitreous or glassy surface._

_It is usually of white or yellowish colour; but is sometimes blue, violet, or black._

In the torrid regions of Africa and Asia there are immense tracts of desert covered only with sand, so dry and light as to be moveable before the wind, and to be formed into vast hills and boundless plains. These are incessantly changing their place, and frequently overwhelm and destroy the travellers whose necessities require them to enter these dreary realms.

Sand has numerous uses. When mixed in due proportion with lime, it forms that hard and valuable cement called mortar. Melted with soda (200) and potash (205) it is formed into glass; white sand being used for the finer kinds, and coarse and more impure sand for bottle glass. A very pure kind of sand which is found in Alum Bay, on the west side of the Isle of Wight, and on some parts of the coasts of Norfolk, is in great request by glass─makers. Sand is also employed in the manufacture of earthenware; and its utility in various branches of domestic economy, but particularly for the scouring and cleaning of kitchen utensils, is well known. In agriculture sand is used by way of manure, to all soils of clayey lands: as it renders the soil more loose and open than it would otherwise be. The best sand for this purpose is that which is washed by rains from roads or hills, or that which is taken from the beds of rivers.

There is a kind of sand which is naturally mixed with clay, and has the name of _Founder’s Sand_, from its being chiefly employed in the formation of moulds to cast metals in. At Neuilly, in France, there is a bed of perfectly transparent and crystalline sand. Each grain, when examined with a magnifying glass, is seen to consist of a perfect six─sided prism, terminated by two six─sided pyramids.

The uses of the different kinds of _Sandstone_ will be enumerated in the account of the rocks (267, 268).

89. _LYDIAN STONE is a kind of flinty─slate, of greyish or velvet─black colour, not quite so hard as flint, opaque, and about twice and a half as heavy as water._

_It is usually massive, and, internally, has a glimmering appearance._

This mineral occurs in beds in primitive clay─slate (257); and is found in Bohemia and Saxony, and also in the Pentland hills near Edinburgh. It was first noticed in Lydia, whence it derived its name.

It is sometimes used as a touchstone to ascertain the purity of gold and silver. This was its use among the ancients. The metal to be examined is drawn along the stone so as to leave a mark, and its purity is judged by the colour of the metallic streak. A good touchstone should be harder than the metals, or metallic compounds to be examined; if softer, the powder of the stone mixes with the trace of the metal and obscures it. A certain degree of roughness on the surface of the best stone is also requisite, that the metal to be tried may leave a trace or streak sufficiently distinct. It must not, however, be too rough, otherwise the particles of the metal will be hid amongst its inequalities, and no distinct trace will be formed. The touchstone should also be of black colour, as this tint shows the colour of the streak better than any other.

90. _FLINT is a peculiarly hard and compact kind of stone, generally of smoke─grey colour, passing into greyish white, reddish, or brown. It is nearly thrice as heavy as water, and when broken will split, in every direction, into pieces which have a smooth surface._

_It is very common in several parts of England, generally among chalk, arranged in a kind of strata or beds, and in pieces that are for the most part either rounded or tubercular._

The property which flint possesses of yielding sparks, when struck against steel, has rendered it an article of indispensable utility in the system of modern warfare. To this substance the sportsman also is indebted for a means of obtaining his game. The art of cutting, or rather of breaking, this stone into gun─flints is of modern date, and was for a long time kept secret. The most absurd and contradictory accounts have been given of it by various writers; and it is only of late that the true mode has been rendered public. It consists in striking the stone repeatedly with a kind of mallet, and bringing off at each stroke a splinter which is sharp at one end and thick at the other. These splinters are afterwards shaped, by placing them upon a sharp iron instrument, and then giving them repeatedly small blows with a mallet. During the whole operation the workman holds the stone in his hand, or merely supports it on his knee: and the operation is so simple, that a good workman has no difficulty in making 1500 flints in a day. The manufacture of gun─flints is chiefly confined to England, and two or three departments in France. In Prussia an attempt was once made to substitute a kind of earthenware or porcelain for flint; and such was, for some time, used by the Prussian soldiers. All the kinds of flint are not equally adapted for guns: the best are the yellowish grey; the dark smoke and ash─grey varieties are also used, but they are neither so easy to be split, nor do they afford such thin fragments as the other; and, owing to their greater hardness, they wear the lock sooner.

Flint is employed in the manufacture of porcelain and glass. For this purpose it is heated red hot, and, in that state, is thrown into cold water. It is then of a white colour, and capable, without difficulty, of being reduced to powder, either in a mortar or by a mill. After this powder has been passed through fine sieves, some aqua fortis is poured upon it, to dissolve any particles of iron which it may have acquired in the grinding. The powder is then several times washed in hot water, and afterwards dried for use. The glass that is manufactured from this substance is perfectly transparent and faultless.

_Glass_ is made by mixing sand, or prepared flint, with a certain proportion of soda (200) or potash (205); and exposing these substances, in a furnace, to a violent heat. When they are in a perfectly fluid state, part of the melted matter is taken out at the end of a long hollow tube. This is done by dipping the tube into it, and turning it about until a sufficient quantity is taken up; the workman, at each turn, rolling it gently upon a piece of iron, to unite it more intimately. He then blows through the tube till the melted mass, at the extremity, swells like a bubble; after which he rolls it again on a smooth surface to polish it, and repeats the blowing until the glass is brought as nearly to the size and form of the vessel required, as he thinks necessary.

If he be forming a common bottle, the melted matter at the end of the tube is put into a mould of the exact size and shape of the body of a bottle; and the neck is formed by drawing out the ductile glass at the upper extremity.

If he be making a vessel with a large or wide orifice, the glass, in its melted state, is opened and widened with an iron tool; after which, being again heated, it is whirled about with a circular motion, and, by the centrifugal force thus produced, is extended to the size required. Should a handle, foot, or any thing of similar kind be required, that is made separately, and stuck on in its melted state.

_Window glass_ is made in a similar manner, except that the mass at the end of a tube is formed into a cylindrical shape. This being cut longitudinally by scissars or shears, is gradually bent back until it becomes a flat plate.

Large _plate glass_ for looking─glasses is made by suffering the mass, in a state of complete fusion, to flow upon a casting table, with iron ledges. These confine the melted matter, and, as it cools, a metallic roller is passed over it, to reduce it to an uniform thickness.

Glass utensils, unless very small and thin, require to be gradually cooled in an oven. This operation is called _annealing_, and is necessary in order to prevent them from cracking by change of temperature, wiping, or slight accidental scratches.

It appears that the manufacture of glass was known very early; but glass perfectly transparent was esteemed of extremely high value. It is stated that the Emperor Nero purchased two glass cups with handles for a sum which was equivalent to 50,000_l._ of our money. The windows of some of the houses of the ancient city of Pompeii, which was buried by an eruption of Mount Vesuvius, in the year 79, were glazed, but the glass was thick, and not transparent.

By many persons flint is used as a test for ascertaining the purity of silver coins. This is done by rubbing them upon the flint; and if the mark which they leave be not perfectly white, they are rejected as counterfeit.

91. _CALCEDONY is a species of quartz, generally of whitish, bluish, or smoke─grey colour; and, when broken, it appears internally dull, and somewhat splintery._

_It is generally found in a massive state, is harder than flint, generally semi─transparent, and 2½ times heavier than water._

The name of this stone is derived from Chalcedon, in Upper Asia, whence it appears to have been originally obtained, and where it is still found in considerable abundance. Several superb specimens of calcedony have been found in Britain, and particularly in some of the tin and copper mines of Cornwall. It occurs in several parts of Scotland; and in many of the countries of the Continent. In the Leverian Museum there was a specimen of calcedony, which weighed more than 200 pounds. Its whole surface appeared such that, at first sight, one might imagine it to have formerly been in a liquid state: it had much the appearance that thick oil has while boiling.

Few stones are susceptible of a higher or more beautiful polish than calcedony. Hence the different varieties of it are cut into ring and seal stones, necklaces, ear─pendants, small vases, cups, and snuff─boxes.

92. _ONYX is a kind of calcedony, generally marked alternately with stripes of white and black, or white and brown._

Its name is derived from the Greek language, and has been given on account of its resemblance in colour to the whitish band at the base of the human nail. The distinction which appears to be made betwixt onyx and _sardonyx_, arises from the colours of the former being arranged either concentrically, or in a somewhat confused manner, and those of the latter in regular stripes or bands.

Both these kinds are highly esteemed by lapidaries, for the formation of vases, snuff boxes, and trinkets of various kinds. Of sardonyx the ancients made those beautiful cameos, many of which still ornament our cabinets. The ingenuity they have shown, in the accommodation of the natural veins and marks of the stone to the figures engraven upon them, is such as to excite, in many instances, the greatest admiration.

It is said that we are entirely ignorant of the country whence the ancient artists obtained the large specimens of sardonyx which are now found in some cabinets.

Onyx is imported from the East Indies, Siberia, Germany, and Portugal.

93. _CARNELIAN is another kind of calcedony usually of a red or flesh colour, though sometimes white, orange, or yellow._

On several of the British shores carnelians are found with other pebbles: but the most beautiful and valuable kinds are imported from the East Indies. These are sometimes so large as to measure nearly three inches in diameter. The kinds principally in request are those of pure white, and bright red colour; and jewellers have the art of changing the colour of the yellow varieties to red, by heat.

No stone is so much in request for seals as carnelian. It is likewise cut into beads for necklaces, and stones for ear─rings; into crosses, bracelets, and other trinkets, which, in India, form a considerable branch of traffic. The amount of the sale value of different kinds of carnelian goods vended by the East India Company in 1807, was 11,187_l._: but, in other years, it has not usually been so much as half that sum.

Formerly carnelians were exported from Japan to Holland; and thence were carried to Oberstein, in France, to be exchanged for the agates of that country, which were exported to China.

The carnelian was much esteemed by the ancients; and many fine engraved carnelians are preserved in different collections.

94. _CHRYSOPRASE, an extremely hard kind of stone, of clear and delicate apple─green colour, is considered to be a kind of calcedony._

This beautiful mineral has hitherto been found only in the vicinity of Kosemitz, and in a few other parts of Lower Silesia. It is susceptible of a high polish, and is much prized by jewellers when its colour is deep and pure. Its colour, however, is so fugitive, that, if kept in a warm and dry situation, it loses the greatest part of it; and if exposed to moisture it becomes much altered. Lapidaries assert, that great care ought to be taken in the polishing of it;—pretending that if, from want of sufficient moisture, or by the too rapid motion of the wheel, it be over─heated, it will become whitish or turbid.

Chrysoprase is generally cut into a convex form, or what jewellers call _en cabochon_; and is set with green taffeta beneath it, as foil. It is used for ring stones, brooches, and other ornaments; and is found to harmonize well with diamonds and pearls. The larger and more impure masses are cut into snuff─boxes, seal stones, and similar articles. Some of the finest specimens of chrysoprase that are known, are to be seen in the cathedral church of Prague, where a small closet is inlaid with them.

Imitations of chrysoprase are sometimes imposed upon the public; but these are easily known by persons who are acquainted with the nature of precious stones.

95. _BLOODSTONE, or HELIOTROPE, is an opaque stone of the quartz family, generally of dark green colour, with a somewhat bluish cast, and marked with blood─red spots or stripes._

_It usually occurs in masses of irregular form; and, when cut thin, is sometimes translucent at the edges._