Thomas Sutton e Robert Macpherson: 1853: panorama di Roma dal Gianicolo

Giovanni Fanelli

 

«Photographic Notes. Journal of the Photographic Society of Scotland and of the Manchester Photographic Society », il periodico edito a Londra da Thomas Sutton per undici anni a partire dal 1856, è una fonte di grande interesse per la storia della fotografia.

Nella nota On the use of bromine (vol. I, 1856, n. 1, 1 gennaio, p. 10), Sutton  riferisce in dettaglio di una fotografia ripresa da lui insieme a Macpherson nel 1853: un panorama di Roma dal Gianicolo.

È questa una notizia di notevole interesse finora non valutata nella storiografia di Macpherson.

 

« On the Use of Bromine

There are certain branches of Photography in which the use of Bromine in conjunction with Iodine, does not appear to be sufficiently recognised. I allude more particularly to the Calotype Process on paper; and the Albumen Process on glass, as practised by certain artists.

If we refer to the early history of the Daguerreotype process, in which the silver plate was merely submitted to the fumes of iodine, we find that it possessed but little sensibility; half an hour being required for a portrait, with a double lens, and a whole morning for a view in full sunshine with a single lens. At the present day, when a certain proportion of bromine is introduced with the iodine, the plate becomes highly sensitive; and a certain proportion of chlorine in addition to this, increases the sensitiveness still more. Also, if the plate, instead of being chemically clean, should contain any traces of oil, the sensitiveness will be heightened still further.

But observe, that in theseexperiments, there are certain proportions of the haloid elements, which give the greatest amount of sensitiveness. Too much or too little bromine, or chlorine affect the sensitiveness considerably.

These facts have an important bearing upon other branches of photography in which the same elements are introduced.

Take for instance an albumenized plate, containing merely iodide of silver. This will be found to possess but little sensitiveness. I will state an anecdote in connection with this circumstance.

When I was in Rome 3 years ago, I took an albumen picture in company with Mr. Macpherson. It was a magnificent sunny day. The view we took was that of the city, from the Janiculum. The sun was at our back, and the whole scene which included a vast extent of Campagna and the distant mountains, lay in one blaze of light. (By the bye, this was entirely wrong; for owing to the absence of shadows, the picture looked flat and tame to a degree. But we must all learn by experience.)

We exposed to this view, one whole hour, and on developing the picture, it was not over done. The plate merely contained iodide of silver. Around each outline of the different objects in the view there was a sort of light halo, which gave to the print a hard, wiry appearance.

Now we have no right to attribute this want of sensitiveness to any peculiar quality of the Albumen… I believe the Albumen to be nearly inert in the matter. The most instantaneous picture ever yet taken was by Mr. Fox Talbot, on an albumenized plate. A Positive print on albumenized paper, prints quite as quickly as one on plain paper. The want of sensitiveness was owing to the want of Bromine. Again, in the Calotype process, unless the weather is very hot, and the paper well sized with some organic matter, it is necessary to add gallic acid to the sensitive solution, in consequence of the absence of Bromine. And it sometimes happens, that  with any amount of exposure there are certain dark parts of the view which will not come out; but which can be obtained by the Daguerreotype, or the Collodion, or the Waxed paper process, in which bromine is introduced.

All these facts appear to me to indicate the importance of combining Bromine with Iodine, in the first preparation, in some certain proportion.

I have succeeded lately in making a very good Calotype paper, in which I have overcome the difficulty of introducing the Bromine. This paper requires no gallic acid to be added to the sensitive solution.

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