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The photographic news
- Bandzählung
- 6.1862
- Erscheinungsdatum
- 1862
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- Englisch
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- F 135
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- Hochschule für Grafik und Buchkunst Leipzig
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- Hochschule für Grafik und Buchkunst Leipzig
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- Bandzählung
- No. 202, Juny 18, 1862
- Digitalisat
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Zeitschrift
The photographic news
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Band 6.1862
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- Register Index 619
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Band 6.1862
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JULY 18,1862.] THE PHOTOGRAPHIC NEWS, 345 and a lamp. of brimstone, as the component parts of the brilliant cadmium yellow. In like manner cobalt blue is seen to consist of phosphate of cobalt and alumina : vermil ion is shown by the side of a bottle of caustic potash, some mercury and a piece of sulphur. Chrome yellow, has for its origin acetate of lead and chromate of potash; emerald green is formed from acetate of copper and arsenious acid and is therefore to be avoided by all those who object to the wholesale employment of this deadly poison in every-day life. Chinese white (oxide of zinc) is represented by a lump of the metal, the atmosphere in the case being, we suppose exhibited as the other component of this colour, it being prepared by burning zink in air. The manufacture of ultra-marine, both natural and artificial, is one of the specialities of this firm, and a magnificent collection is to be seen of this beautiful colour in all varieties of tint, together rith the lapis lazuli from which the natural colour is obtained, and the quartz, carbonate of soda, sulphur and china-clay. • THE PRINTING OF POSITIVES. BY E. BEYNAUD. "me influence on the beauty of positive pictures exercised by the circumstances in which the printing is performed, 18 well known to photographers generally. For instance, a hegative, which on certain occasions yields but a poor and valueless print, would frequently, if obtained under better fonditions, furnish a satisfactory production. The importance, then, of an investigation leading to the determination of the best conditions, according to the nature of the negative, in order to obtain the best possible result, can easily be conceived. , I will briefly detail some hints, the result of my expe- "enceonthe subject. The chief points to be considered are:— 1 The intensity of the light. 2 , The nature of the paper employed* t The proportion of free nitrate of silver which it con- The intensity of the light, in which the operation of Printing is performed, must always have a certain relation the intensity of the negative. A negative that has Deen exposed too short a time in the camera presents, as is "! known, large transparent portions without detail, Mich produce deep shades or masses of black in the posi- prints, whilst the lights are opaque, and the middle Mes are wanting. Printing from such a negative requires ?right light in order to be successful : in such a case the । M light of the sun is to be recommended. If, on the other 304, the negative has been exposed, contrast will be Anting in the light and shades, the delicate half tones the lights being effaced, and those of the shades too v„advanced. Such a negative exposed to an intense light o yield a grey and monotonous print; whilst on the । perhand a weak light will produce more vigour. The folio w- 1,8 is an excellent means for obtaining a suitable degree of toninous intensity at a time when the rays of the sun are t) brilliant :—it consists in placing between the glass of wh; printing-frame and the negatives, a sheet or two of Bytepaper, quite homogeneous and more of less transparent, anathis.means the intensity of the glass becomes moderated, Pr Arrives at the negative in a proper condition for the fiction of a good print. bet must here remark, that it is from the relation existing dedeen the lights and shades of the negative, that we can fromesthe proper degree of light to be employed, and not tain I he absolute opacity of the lights. For instance, cer- if tParts of a negative may be extremely opaque, and yet, e tune has been too long, the whole of the negative * J Btssarander stand here not the intimate nature of the paper, but that of the ."ng a bumhenizdhgs it appropriate for the purposes of photography, as will present but little contrast; in this a feeble light is indicated as the best for producing a good print. Thus, then, to state the matter briefly, since a feeble light, other things remaining the same, produces more contrast between the extreme tones of the prints, such a light is to be employed when the negatives are too weak or uniform ; whilst an intense light, on the contrary, produces more monotonous images, this light is appropriate for harsh negatives, that is to say, for such in which the lights are too opaque and the shades too transparent. But these phenomena are modified more or less by the nature of the positive paper; it is, therefore, necessary to study the properties of this substance, and to examine the influence of its elements on the beauty of its prints. In the first place let me remark that a large proportion of free nitrate of silver acts like an increase in the intensity of the light. For instance, paper sensitized in a bath of twenty per cent, or 100 grains to the ounce, will produce, with the same negative, and the same light, a more monoto nous or less contrasted print than if it were sensitized in a bath containing only fifteen per cent, of nitrate of silver. Hence it may be deduced, that paper, sensitized in a bath rich in silver, is preferable for harshly contrasted negatives ; whilst, on the contrary, paper sensitized in a weak solution is adapted to feeble and uniform negatives. Nevertheless, it must be observed that, since the vigour of tone depends also on the excess of nitrate of silver, the proportion of the latter cannot be diminished sensibly below fifteen per cent, if the toning and the fixing are to be properly effectuated. I will now examine the influence of the first preparation of the paper. Positive paper is divided into two distinct heads :— Plain salted paper. Albumenized paper. Ordinary plain salted paper contains simply a certain proportion of some soluble chloride. Albumenized paper contains, besides this chloride, organic matter—albumen. After sensitizing, the former contains chloride of silver ; and its surface is covered with a film of nitrate of silver. The latter contains, besides these two salts, a large pro portion of a peculiar body but little known; the same which is produced when a solution of nitrate of silver is poured into albumen. The fact is described and perfectly explained in an excellent article by Abb Pujo.* Now this body, which the author denominates albuminate of silver, has the peculiarity of producing extremely vigorous or harsh images. It is to this salt that albumen paper owes the well known property of producing, with the same nega tive, prints endowed with much greater contrast than is found in those obtained on plain salted paper. It is easy to comprehend, therefore, that the proportion existing between the albuminate and the chloride of silver, will exercise considerable influence on the prints. A largo excess of the albuminate is adapted for gray or monotonous negatives, whilst negatives with great contrast require a large proportion of the chloride. Insnort, the proportion between the albuminate of silver and the chloride of silver modifies the results, in the same manner as an excess of the nitrate, or the intensity of light; and it is on a correct relation between these four elements that positive printing depends for its success. It is impossible to determine the proportion to be observed between these elements in accordance with the different degrees of intensity of the negatives ; experience alone can teach the peculiar rules to be applied in each case. I shall occupy myself further with the study of the influence which the above-mentioned elements exercise on the fixing and toning of prints, that is, the tone and vigour they assume in the gold bath and the fixing solu tion, hyposulphite of soda, and lay the particulars before the Society.—Moniteur. * See pp. 201 and 302, Vol. v, Puorognaruo NEws,
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