1044 PROCEEDINGS OF THE THIRD ENTOMOLOGICAL MEETING 



with a coating of greasy ink and then placed in water, it is then wiped 

 carefully with cotton wool and the coating which has not been acted 

 on by hght, being soluble, washes away, taking the ink with it, leaving 

 the ink on the parts which have been acted on by hght. The ink image 

 on the zinc plate should now be a true representation of the original 

 copy. 



The thin film of ink is next reinforced by very fine powdered asphal- 

 tum and is now ready for etching. After examining the plate to see 

 if the lines are all correct the plate is now placed in a weak solution of 

 acid which etches the parts not covered by the mk image. Considerable 

 care and skill are required at this stage as a httle carelessness means- 

 the loss of fine lines. 



After a short etch the image on the plate is again strengthened to 

 enable it to stand a stronger solution of acid, this process of etching 

 being repeated till the white spaces are deep enough to make it im- 

 possible for them to take ink from the printing machine roller. 



After trimming away the superfluous metal and mounting on wood 

 the block is ready for the printer, each line of the drawing which has 

 been reproduced standing in relief from the rest of the metal. 



The following are the points to be observed in preparing originals 

 for line work. All drawings should be made with clear black lines on 

 white paper or card. Eough paper should be avoided. Care should 

 be taken that all the hnes are drawn firmly ; scratchy or grey Imes, 

 produced by the ink being thinned down, are not permissible. 



Drawings for the fine process are better if made larger than the 

 required size, reduction giving sharper and clearer results. It should 

 be borne in mind that each line reduces in breadth as well as in length. 

 All lettering should be neatly and clearly put in, care being taken to 

 make all lettering sufficiently large to stand reduction. This point is 

 often lost sight of, the result being that lettering which appears perfect 

 on the original is unreadable when reduced. All lettering and in fact 

 every line of the original should be perfect and complete, as alterations 

 on the finished block are extremely difficult. 



The most suitable scales of reduction are one half or two-thirds the 

 size of the original. 



Half-tone process. 

 The Half-tone process is used when it is desired to show the grada- 

 tions fi'om black to white with the intervening tones. This is also a 

 photographic process but to obtain the desired effect it is necessary to 

 make a special negative which is broken up into dots varying in size. 



