Ill ( IMl'.l K. I'Ml. 



KNOWLEDGE. 



463 



the beginning of the first till the end of the third — 

 varies from a minute and a half to three minutes if 

 an arc lamp of the enclosed t\"pe is used, as this 

 gives the greater percentage of violet or acti\-e ravs 

 of light, to which the plates are most sensitive. 

 The exposure with the o|5en type of arc lamp is 

 about three times as long 



The exposed plate is now dexelojicd in the 

 ordinar\- waw and it is afterwards reduced (in 

 densit\), or, to use a trade term, "cut in." b\- letting 

 a solution \\hich diminishes the size of the "dots" 

 flow over it. This is done until the "dots" are of 

 the size necessar\' to gi\c the reipiisite brightness. 



The object of the burning or baking is to make the 

 coating into a hard enamel. 



The plate is now passed on to the etchers, who 

 place it in a solution of perchloride of iron. This 

 eats awa}' the copper between the dots, and thus 

 leaves the image standing up in relief, the enamel 

 not allowing the solution to touch the "dots." A 

 rough jiroof is now taken of the print in order to see 

 what further etching is required. This fine etching 

 (see Figure 9) is done b^• stoi)ping out, with a resist- 

 ing varnish, parts which do not require an\' further 

 etching, and the high lights are then etched up 

 so as to give more brightness and detail. 



I'lL.liKi; 11. Routing away useless metal. 



By using the two handles the router can be made to go in 

 any direction desired. 



iMi.uui; 12 



In this way it is 



when it w 



Lining and bevelling the plate, 

 ot ready for nailing on to the wood 



be type-high. 



The finished negative is now dried and given to 

 the printer. After he has examined it to see how 

 long it will take to print, he places it in contact 

 with a piece of copper, which has been made sensi- 

 tive to light — both being put into a printing frame, 

 which enables great pressure to be exerted to bring 

 the two close together. The piece of copper is 

 sensitized with a solution, composed of white of egg, 

 fish glue and bichromate of ammonium. The 

 frame is put in front of a strong light, which, acting 

 on the sensitized copper through the transparent 

 parts of the negative, prints the image on to it. 

 The print on the copper plate is then developed in 

 water, which dissolves away the solution not acted 

 upon bv the light, and it is afterwards burnt in 

 over a Bunsen burner (see Figure 7). The result is 

 a print rnade up of a series of " dots " and squares, 

 ranging from fine white '" dots" in the blacks to fine 

 black " dots " in the lightest parts of the subject. 



When the etchers have done all that is necessary 

 the plate is then passed on to the engravers (see 

 Figure 10), who take out unnecessary spots and 

 engrave up what lights require brightening or what 

 darks require a little burnishing so as to give a 

 greater depth of colour. 



The block — as it ma\' n(.)w be called — is now ready 

 for the finished proof to he taken, and after that is 

 done it is given to the mounter, who fastens it on to 

 wood of such a depth as to make it as high as type. 

 It can now be printed side by side with type. 



The methods of working and the apparatus used 

 have, within the last few years, been brought to 

 such perfection that it is now possible for a block to 

 be completely made — ready to be put on the printing 

 press — within one hour from the time the photograph 

 or drawing is placed in the operator's hands. This, 

 of course, is onl\' for a hurried illustration ; the usual 

 time taken over a block is from four to five hours. 



