The Sepia Toned Image, A Color Change To Gold And Toning To Ferrocyanides
Sepia toning, as written in the article to selenium toner, is probably the most popular in photography. On par with selenium, sepia also gives the press a longer life, besides giving the classic color “sepia” to photographs.
The principle of operation of the color change is very simple: the silver content in the press, not being a noble metal, it tends to deteriorate because of the presence akusaraprosound, in the atmosphere, hydrogen sulfate, turning into silver sulfide (dark color ). Try to leave in the open any objects of silver and you will notice how, even in a matter of a short time, you tend to get dirty, with brownish areas. This same process touches to photos, as they are printed well: over time it will create the spots, especially in the light parts of the picture, no longer correctable.
The sepia solves this problem with the chemical reaction in the dark room: in practice, the transformation of silver in silver sulfide is performed on the entire picture (from which the brown color) thus avoiding that the time effects the chemical reaction only on some parts of the same.
As for the selenium toner, prepare a bowl of water with submerged a copy of the press who want to turn. We will serve as a reference for the next steps.
The first bathroom to realize is that said bleaching: this must be to contain the chemical compound in a ratio 1-35, 1-40. Normally you use of potassium ferricyanide (10 g / liter respectively) combined with the potassium bromide (25g / liter). The solution can be used several times, it does not undergo a true process of aging.
The second bath, the one sepia or sulfidation / sulfation is made with a dilution of 1-10 / 1-15 sodium sulfide (1 liter of water, 10-15gr sodium sulfide).
By varying dilutions, both in bleaching in sulfation, we can change the color change. For example, a higher dilution of the bleaching can whiten “less” photography by having the second bathroom to act (and therefore the sepia effect) only on the softer colors not touching the darker ones.
There is the possibility of preparing a third bathroom, an anti-bleaching (also called reductant) whose purpose is to counteract the bleaching, in case you have exaggerated. Its preparation is simple: take the development solution for the cards and used a dilution in water equal to 1-1 or 1-2.