The Dictionary Of Photography

A True Historic Record Of The Art & Practice Of Photography 100 Years Ago.

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Isochromatic Photography
FeS047H20 = 278. Synonyms : Ferrous Sulphate, Protosulphate of Iron, Copperas, Green Vitriol. The crystals should be of a bluish-green colour, free from any adherent brownish rusty powder, which is caused by the action of the oxygen of the air, the product being an oxy-sulphate: to this action is also due the deteriorations of solutions of this salt. When this change in colour of a solution is noticed, it should be rejected and fresh solution used. Solubility: I in 1*5 of water; insoluble in alcohol and ether.
Isinglass. A crude gelatine, obtained from the swimming bladder or sound of the sturgeon. The finest is exported from Russia. Manufactured gelatines are generally preferred for photographic purposes.
Isochromatic, Orthochromatic, or Orthoskiagraph^ Photographycoloured or suited for
colour;I sketch or paint
in light or shade). These terms are used to distinguish that branch of photography which attempts to render in correct or more truthful gradations the colours as seen by the human eye. The merest tyro is too soon aware that the sensitive salts of silver are incapable of translating colours into correct mono-chrome as seen by the human eye. Thus a bright yellow sunflower or skein of yellow wool is reproduced by photo-graphy as black, and many shades of blue are, though visually dark reproduced as nearly white. In the article upon the Spectrum (g.v.) it will be seen that a ray of white light is split up into its various constituent rays of different colours : the brightest of these colours to the human eye is yellow, and then orange, two colours which are reproduced by black. As the question of colour is so closely connected with this subject, a brief consideration of colour will not be out of place. No sub-stance known possesses any colour of itself. Colour is caused solely by the action of the substance on the light which falls upon it. Natural bodies possess the power of absorbing the light which enters them, and they have this power in a selective manner; that is, some objects select and absorb certain of the coloured rays and reflect others. When all the light is wholly absorbed, the substance appears black; but when all the rays of light are equally but not entirely absorbed, grey is the resultant tint,