THE INDUSTRY OF ALE NATIONS.

Francs. Dollars.

Flint glass disc 22 inches in diameter, and weighing 80 pounds, at

5 francs per lb.,. 400 80

Softening and moulding the mass,. 140 28

540 108

Crown glass disc, weighing 50 lbs., at 5 francs per pound, . . 250 50

Softening and moulding,. 200 40

450 90

Such a flint glass disc as the above would at former rates have cost more thantwenty-two times as much, or about $8000, and, if furnished at all, wouldhave been in all probabilty of inferior quality. The chief cost of refracting tele-scopes has formerly been in the object glasses. The Cambridge object glass (oneof the largest in use) is about 16 inches in diameter, and its cost is understood tohave been about $15,000, the whole instrument costing about $25,000. It seemsreasonable to hope that hereafter refracting telescopes of larger size may befinished at a greatly reduced cost, although we must remember that the processof grinding, and of giving an exact figure to the lenses, still remains a greatand difficult work.

Very few specimens of optical glass are seen in the present Exhibition,and none of remarkable size. See Nos. 12 and 19, Class 10.

Artificial Gems .—The visitor at the Crystal Palace must have noticed in theAustrian Court the collection of artificial gems shown by A. Pazelt, of Tuman,Bohemia (No. 2, Class 24, Austria). These pastes , as they are usually called,rival in color and lustre the natural gems, and are in fact inferior to them onlyin hardness (except the diamond whose adamantine lustre cannot be imitated).The material from which these artificial gems are made is a very colorless andlimpid flint glass, called strass, after its inventor. Its peculiar limpidity and lus-tre is due not so much to the great quantity of lead it contains as to a portionof the silica being replaced by boracic acid. Its composition according to Wie-

land is:—

No. 1. No. 2. No. 3.

Ground rock crystal,.100 - 100

Sand,.. 100 -

Pure minium,.156 - 154

White lead, ......... - 171 -

Purified caustic potash, ....... 54 32 56

Boracic acid, or its equivalent of borax, ... 7 9 6

Arsenious acid,.£ ^ $

The colorless limpid glass thus obtained is the basis of all the artificial glassgems, and may be colored by the metallic oxyd? already noticed. Thus topazis imitated with glass of antimony and purple of cassius or oxyd of iron; rubywith purple of cassius ; emerald with oxyd of copper or chromium; sapphire withoxyd of cobalt; garnet with purple of cassius, glass of antimony and peroxyd ofmanganese, and so on.

The principles of glass painting have already been discussed in an article towhich the reader is referred.

BANK-NOTE ENGRAVING.

T HE specimens of this art in the Picture Gallery have excited the admiration ofevery visitor who has given them a careful examination. Nothing is renderedmore familiar to us by habitual use than a bank-note; yet, of the thousands whohandle them daily, there are very few who bestow even a passing glance upon theirvignettes and other designs, or who are acquainted with the mode of their produc-tion. In truth, the value of a bank-note as the representative of the precious met-als, takes away all idea of its worth as a work of art, and yet in this latter respectit is entitled to notice. Not only has this branch of engraving been carried to thehighest perfection, but it is interesting to us to consider that this perfection is dueexclusively to American invention.

The prevention of forgery in bank-notes, bonds, certificates, and similar prom-issory paper, is chiefly due to the costly style of their execution. If the very bestartists are employed in drawing the designs, and the best engravers in executingthem, forgery becomes not only difficult, but unprofitable—a bank-note plate at thecost of one thousand dollars is much less likely to be imitated than one that costs onehundred. And this consideration, evidently a correct one, has furnished one ex-ample of the valuable alliance between business and art which is common in highlyrefined communities; though it must be confessed that in this case the union is notdue to taste only. But whether due to taste or economy, the result is the same,and the lover of art will find his curiosity amply repaid if he, will study the beauti-ful specimens of bank-note engraving in the picture gallery, exhibited by Messrs.Rawdon, Wright, Hatch & Go., 48 Exchange Place, New-York city, and by Dan-forth, Wright & Oo., also of New-York.

The present style of bank-note engraving originated in the discovery, by our

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ingenious countryman Mr. Jacob Perkins, of the method of engraving on steelwhich gives to the productions of this art a durability never before known. Bymeans of this method the works of the artist may be reproduced and multipliedindefinitely. A steel plate properly prepared is engraved or etched in the usualway. A cylinder of very soft steel, of from two to three inches in diameter, ismade to roll forwards and backwards on the surface of the steel plate, which in themean time has been hardened, until the impression of the engraving is seen uponthe cylinder in alto relievo. The cylinder is then hardened, and is rolled in thesame manner upon the surface of a copper or soft steel plate; the result is a perfectcopy of the original plate. This style of engraving is very economical where agreat, or an indefinite number of impressions are to be used—more than half amillion of impressions have been printed from a well-hardened steel plate, while acopper plate is deteriorated by printing six thousand impressions. A hardenedsteel plate will in fact print more proof impressions than six copper plates will givecommon impressions. At the very lowest estimate, the relative values of the twokinds of engraving are as one to four, apart from the consideration that of the cop-per plate impressions many are imperfect. On the other hand, it must be remem-bered that this method of engraving is only employed where a number of impres-sions is required sufficient to wear out three copper plates; a less number wouldnot warrant the cost of making a steel plate. From this it appears that much thelargest proportion of the plates now in use must be of copper. The art of steelengraving is very extensively applied to the embellishment of standard works, andto the illustration of books of instruction and science. But, to return to bank-note engraving; besides the medallions and vignettes on the notes, there are otherforms of engraving consisting of a variety of circular, oval, and rectilineal shapes,exceedingly variegated and interlaid, and exhibiting a most curious, beautiful, andsymmetrical intermingling of geometrical figures. All these are produced by aningenious and remarkable machine invented by our countryman Mr. Asa Spencer.This machine has been justly compared, in its power of presenting an infinite diver-sity of patterns, to the far-tamed scientific toy, the kaleidoscope. It possesses thispeculiarity of the kaleidoscope, that the turning of a screw, like a change in the po-sition of Sir David Brewster’s instrument, gives rise to an entirely new pattern, suchas has never been seen before, and may never recur again. This pattern, however,may be preserved and perpetuated by the transferring process. The forms producedby this machine, which is called the geometrical lathe, will be found on inspectionto contain an intricate and mazy concretion of lines and dots, which to the practisedeye constitutes the best practicable means of identification. And to these forms isgiven the effect of a beautiful combination of copper-plate and letter-press printing,by making the lines which in one scroll or block are white, in the next black, and soalternating through the whole series, in which the figures themselves are, except inthe shading, precisely alike. It is worth mentioning, as an example of the illiberaljealousy which merit has often to encounter, that Sir William Congreve employedan artist of the first talents to attempt an imitation of some of the specimens ex-hibited by Mr. Perkins in England in 1820, when he was endeavoring to bring his ,invention into use. The attempt was pronounced by his own countrymen a totalfailure, particularly in the small writing and engine work; though Sir William main-tained the opposite opinion, and published a pamphlet for the purpose of impressingthis opinion on the public. This “Record ” which has for its high object to pro-mote the knowledge and diffusion of art among the nations, and to remove thosenarrow national prejudices which have interfered with such diffusion, is the properplace for holding up to public rebuke the conduct of Sir William Congreve.

In the making of plates, cylinders, circular or other dies, the best cast steel isused. For the purpose of transferring fine and delicate engravings, a surface stra-tum of the steel plate or cylinder, descending to about three times the depth ofthe engraving, is decarbonated, by which it is softened and rendered fit either fortransferring or engraving designs. This is a process demanding great expertness.After any piece of steel has been decarbonated, whether a plate, or cylinder, ordie, it must, previously to being put under the press, be again carbonated, or re-converted into steel capable of being hardened. This carbonization, or reconver-sion into steel, is effected by means of annu al carbon. Here again is a processwhich can only be safely attempted by the most experienced workmen. It wouldbe impossible to describe by words only, the two criteria of color and sound onwhich the successful execution of this delicate task depends. They are only to belearned by actual observation. They are among the mysteries of art. Before con-cluding this brief notice, we will venture once more to ask the curious in the finearts to look at the vignettes on the specimens of bank-note engraving in the gal-lery of paintings in the Crystal Palace, however familiar they may seem to him.He may be surprised to discover in them some unexpected beauties. lie will notonly admire their correctness in perspective, in drawing, and in shading, but alsothe rare finish of their engraving. He will derive pleasure, moreover, from thevaried and ingenious representations of the pursuits of industry on the land andon the ocean; and may be led into an agreeable train of thought by contemplatingthe pictorial views of that labor and art which supply

“ Tho fireside enjoyments, home-born happiness, 1 ’

of many millions of free and happy people on both sides of the Atlantic.