220 report — 1859. 



need only be prolonged until it has become of the desired tone and colour; 

 always remembering, that during the subsequent operation of drying, &c. 

 it will become of a somewhat darker tint than when taken out of the fixing 

 bath. 



66. On removal from this bath, the pictures must be allowed to soak in 

 a large quantity of cold water for ten or twelve hours. There must not be 

 very many in the dish at a time, and the water must be changed at least 

 three times during that interval; they must then have boiling water poured 

 over them (of course in a porcelain dish) two or three times, and lastly be 

 pressed dry between sheets of clean blotting-paper (14) (these may be used 

 several times, if dried), and then allowed to dry spontaneously in the air. 

 When the pressure frame is not in use, a pile of these finished positives may 

 be put in, and kept tightly screwed up all night ; by this means they will be 

 rendered perfectly flat and smooth. 



67. The picture is now complete. It must be borne in mind, however, 

 that the light and shade are reversed by this operation, the track of the 

 luminous image along the paper being represented by a white instead of by 

 a black band, as in the original negative. Should it be desired to produce 

 exact facsimiles of the negatives, it can be done by employing one of these 

 positives as a negative, and printing other positives from it ; in this way, 

 the light and shade, having been twice reversed, will be the same as in the 

 original negative. 



63. In some cases it may happen that, owing to a partial failure of gas, 

 or imperfection in the sensitive sheet, an image may be so faint as to render 

 it impossible to print a distinct positive. The gap that this would produce 

 in a set of pictures may be obviated, and with very slight sacrifice of 

 accuracy, by forming an artificial or secondary negative in the following 

 manner: — 



69. Print a copy on positive paper, of any intensity which will show the 

 most distinct impression ; then without fixing, and with a pair of sharp 

 scissors, accurately and carefully cut out the part corresponding to the 

 impressed portion of the negative. Expose this piece to the light until it 

 has become perfectly opake, and then it can either be cemented over the 

 imperfect original sheet, or on a clean sheet of paper, and used as an ordinary 

 negative. 



It is astonishing what accuracy and quickness in cutting out even the most 

 intricate pictures, may be obtained with a little practice ; the error of the 

 scissors is generally within the error of measurement. 



Supplementary Notes to the above description, embodying some slight changes 

 in the process made at Kew. By C. Chambers. 



1. After reaching the stage described in art. 28, a pile of paper is to be 

 made up, in which eight plain (unwaxed) sheets alternate with one waxed 

 sheet, and in this state is to be placed between hot plates and subjected to 

 high pressure for several hours, when the mass of paper will be found to be 

 completely permeated by the wax. The operation is to be repeated four or 

 five times, and the sheets, being separated after cooling, will be ready for 

 iodizing. 



The operation of pressing is best accomplished with the pappr not folded, and 

 of the full size as received from the maker, so that the edges which retain super- 

 fluous wax may be cut off and rejected, and the sheets then cut into pieces of 

 the required shape. Piles half an inch in thickness may be done at once in 

 this way, and using several series of hot plates, any quantity of paper may 



