1817.] 



THE CIVIL ENGINEER AND ARCHITECT'S JOURNAL. 



279 



was in this mode that M. Daguerre operated ; for in his original inveatioo 

 iodine alone was used. The inconvenience of so long an exposure to light, 

 however, especially in taking portraits, was seriously felt, and after many 

 investigations for the purpose of quickening the process, it was discovered 

 that bromine in addition to the iodine would act with great efficacy as an 

 accellerator; and now Daguerreotype pictures are by this means some- 

 times taken in less than a single second. 



In submitting the iodised plate to the action of bromine the greatest care 

 is required ; for if the bromine be deficient, the plate will not be sufficiently 

 sensitive, and if the bromine be in excess, the picture will either not be 

 formed, or the plate will be covered with a mist. The simplest way of 

 operating is with the common bromine pan, which is a shallow flat-bot- 

 tomed vessel, with a cover of glass, ground tight to the edges, to keep in 

 the sufTocating vapour. A ledge inside the vessel holds a support, usually 

 made of slate, for the plate to rest on with its silvered side downwards. 

 It is most desirable to ascertain accurately the strength of the bromine 

 water, and to have it uniform in all operations ; a close approximation to 

 uniformity may be obtained by mixing a given measure of distilled or rain 

 water with saturated bromine water. The saturated bromine water is 

 easily procured by pouring some bromine into a stoppered bottle of water, 

 taking care that there is more bromine than the water will dissolve. A 

 convenient solution for use is 40 parts of water to 1 of the saturated solu- 

 tion, which will then be of the colour of pale sherry. As much of this 

 diluted solution must be poured into the bromine pan as will cover the 

 bottom, and then introduce the iodised plate. If the plate has been well 

 iodised, the vapour of bromine will impart a rose lint to it in about 

 thirty seconds or less ; but it is safer to remove the plate before it has re- 

 ceived as much bromine as will give extreme sensitiveness rather than run 

 the risk of giving it an excess. The plate is usually returned to the iodine- 

 box for a few seconds, but this is not absolutely necessary. It must be 

 observed that in the process of bromining, the length of time required will 

 depend iu a great measure on the iodising. A plate that has but a pale 

 gold tint will require less bromine than one that has become of a darker 

 colour. The tone of the picture is much improved by adding about 50 

 drops of muriatic acid to each ounce measure of the saturated bromine. A 

 preparation of bromine has lately been made, called " accellerating powder," 

 which is very convenient in use, and produces a pleasing tone of colour. 

 It has also the advantage of greater certainly, if a fresh quantity of the 

 powder be used each time; for this, as well as the bromine water becomes 

 rapidly weaker by exposure, therefore it is advisable for beginners to renew 

 the accellerating mixture each time of using. When experience has been 

 gained, it will be sufficient to add a few drops of the saturated bromine 

 till the water attains the proper colour. Care must be taken to exclude 

 the light of day from impinging on the plate after it has received the sensi- 

 tive coating, and it must be viewed only by the light admitted through the 

 chink of a door or of a window shutter. The necessity for this precaution 

 will be evident on considering that the rays of light which are sufficient to 

 produce an impression in the camera in a few seconds are admitted through 

 but one small aperture, and that when a plate is exposed to the light it 

 receives rays from all surrounding objects. 



When the plate is properly prepared and enclosed in the sliding case 

 which accompanies the photographic camera, we have arrived at that part 

 of the operation which requires the most judgment and experience — the 

 exposure to the influence of light. The first things to be done are to select 

 the point of view, and to adjust the focus of the lenses so as to obtain a dis- 

 tinct image with sharp outlines on the trial screen of ground glass. If 

 the object to be taken be a building or a vievv, no directions need be given, 

 as the judgment of the artist will guide him ; but in taking a portrait much 

 attention to minute particulars will be requisite to bring out a satisfactory 

 result. Tlie following general directions will be found useful aids in the 

 endeavour. Care must be taken that no dark shadows fall on one side of 

 the face, as they will be exaggerated in the Daguerreotype likeness and 

 give great sternness to the expression. To avoid this, it is almost indis- 

 pensable to operate in the open air. The camera should be elevated to the 

 level of the face, in order to obtain the greatest perfection in the delineation 

 of the features. The dress should not expose any large surface of white, 

 for those parts would be solarised before other parts have had sufficient 

 light ; therefore it is usual, when collars or shirt-fronts appear, to cover 

 them with black, which is withdrawn when half the time of intended ex- 

 posure to light has elapsed. When the sitter has large overhanging eye- 

 brows, it is extremely difficult to prevent the eyes from being thrown in 

 shade, which gives a fearfully disagreeable expression ; it is best in those 

 cases to take the likeness en profile. The background should be sufficiently 



light to throw out the figure and face without being too bright ; but this is 

 a point that the judgment and taste of the operator will determine, bearing 

 m mind that the red rays make little more impression on the plate than 

 black, and that the brightness of yellow and orange is also greatly dimi- 

 nished. Another point which it will be advisable to attend to is the per- 

 sonal appearance of the sitter. If a child, or a handsome young person, 

 be the object, the focus should be as accurate as possible ; but for those 

 advanced in age, or who have defects on the skin, it is advisable to adjust 

 the focus of the lenses so as to obscure those defects by blending the rays 

 of light. There are many other minor points that will require attention, 

 but taste and experience will guide the artist to perfection in such details ; 

 and the general directions here given will be found sufficient for most occa- 

 sions. 



When everything is properly adjusted, the case which contains the pre- 

 pared plate must be substituted for the screen of ground glass, and the 

 slide that exposes the plate to the image must be drawn up, taking care 

 not to shake the camera so as to alter its position. The instant that the 

 light impinges on the plate an effect is produced on the sensitive iodine 

 coating ; and it is the most critical point of the whole process to determine 

 how long the action of light should continue. As there is no visible im- 

 pression made on the plate by the rays of light, to guide the operator, he 

 can only judge by experience— after numerous failures and afewsuccesful 

 efforts— when the light should be excluded. To aid in gaining this expe- 

 rience, however, some general directions may lessen the number of 

 failures. 



We will suppose the artist to have prepared plates in a uniform manner, 

 and of such a degree of sensitiveness, that they will lake a building on 

 which the sun is shining in three seconds. When the sun is obscured, 

 the plate will require six, eight, ten, twenty, or thirty seconds to suffici- 

 ently receive the impressions of the ray from the same object, according 

 as the clouds are rarer or more dense. As so much, therefore, depends 

 on the state of the atmosphere, and as a second more or less will effect a 

 much greater change when the sky is bright than when it is obscured, it is 

 always much better, especially for tyros in the art, to operate on a gloomy 

 day, for then the error of a few seconds will not much impair the eflect ; 

 taking care to give, under such circumstances, what is considered rather 

 an excess of light. In taking the largest-sized view that the camera will 

 admit, a diaphragm is used to confine the rays to the centre of the glass, 

 for the purpose of avoiding the effects of aberration ; and as the diaphragm 

 greatly diminishes the quantity of light, it will be necessary to make al- 

 lowance in the time of exposure in proportion to the covered surface of 

 the object-glass. For portraits, it is desirable of course to diminish the 

 time of sitting to the least possible quantity, and some portraits have been 

 taken in the fraction of a second, but the chances of success under such 

 circumstances are greatly diminished. It is hazardous, therefore, to 

 attempt to operate in so bright a light, and the effect is not nearly so 

 pleasing, even when successful, as when the portrait is taken under a more 

 sombre influence. We have been most successful when operating in the 

 open air, about six o'clock on a summer's evening, with the sun obscured 

 by light clouds, allowing the plate about twenty-five seconds exposure to 

 the light in the camera, which is one of Mr. Ross's manufacture, with 

 double lenses and If-inch aperture. When portraits are taken in a room, 

 a longer time is required, because the light is then screened from the sitter 

 on all but one side. Much, again, will depend on the colours of the 

 objects to be depicted. If they be light, the impressions will be more 

 quickly made, and if dark an additional time should be allowed. The 

 effect when a Daguerreotype plate has had too much or too litlle light is 

 easily perceived. Too much light will cause the white parts of objects to 

 appear blue, the blacks become brown, and the finer demarkations of 

 shading are destroyed. Such a picture is said to be " solarised" or 

 " burnt." On the contrary, in a picture which has not had sufficient light, 

 the lights and shadows are in strong contrast, and the darker portions of 

 the object are not developed. With a still less degree of light, there is a 

 general feebleness of impression, which no length of exposure to mercury 

 vapour will strengthen. 



The plate having been withdrawn from the camera, it is next transferred, 

 in the dark, to the mercury-box, to bring out the latent picture. This is 

 the most interesting part of the process, for now we have to ascertain 

 whether all the trouble and care we have bestowed have been thrown 

 away, or whether we have succeeded in obtaining a perfect picture 

 most exquisitely finished. The impressions made on the iodine and bro- 

 mine by the rays of light, though invisible, have yet such efficacy as U» 

 expose those portions of the silvered plate to the action of the vapour «f 



