Traditional black and white photographic paper tone control (Tone): Selenium toning and sepia toning formulas and lifespan extension

1. The dual mission of chemical toning: aesthetic toning and physical anti-oxidation shield

In the traditional black and white silver salt darkroom, the silver salt photographic paper after development, fixation, and water washing is only a semi-finished product. Chemical toning gives the work a top-notch gallery-level texture:

1. Oxidation vulnerability of metallic silver:

• The black image formed in the emulsion layer of photographic paper is composed of ultra-fine metallic silver particles (Silver Grain);
• When exposed to air containing car exhaust (sulfur dioxide), ozone and paint volatiles, silver particles are easily oxidized to form traces of silver sulfide spots, resulting in redness, yellowing and fading of dark parts and "Silver Mirroring".

2. Precious metal chemical replacement and protective packaging:

• Selenium or Sulfide ions in the toner react chemically with the metallic silver on the surface of the photo paper:
  $$Ag + Se \to Ag_2Se \quad (\text{Generate extremely stable silver selenide})$$
• The generated silver selenide or silver sulfide is extremely chemically inert and will not fade at all even in the face of strong acids and strong oxidants, extending the storage life of the photo paper from decades to hundreds of years.

2. Kodak Rapid Selenium Toner (KRST) actual combat

Selenium toning is a lifelong essential darkroom signature technique of landscape photography master Ansel Adams:

1. Three classic dilution ratios to control hue and contrast:

• 1:9 Powerful Color Ratio: The dark areas of the photo paper quickly transform into gorgeous and cold purple-brown/red eggplant tones, suitable for portraits.
• 1:19 standard color ratio (recommended by Adams): Without changing the warm and cold tone of black and white photos, the maximum black density (D-max) soars from 2.0 to more than 2.3! The shadows are as dark and deep as if they were painted with ink, and the highlights are transparent and three-dimensional.
• 1:39 Pure Protective Color Ratio: The color will not change at all visible to the naked eye. It is only used to coat the surface of the silver particles of the photographic paper with a protective shield to achieve archival-level preservation.

2. Operation process and end point judgment:

• Carry out under bright white light;
• Pour 20℃ toner into the tray, slide the washed wet photo paper into the tray, and shake gently;
• Place an untoned comparison sample next to it:
• Pay close attention to the deepest dark part of the picture: around 3 to 5 minutes, the deep dark part, which was originally slightly gray and blue, suddenly seemed to be awakened and became extremely dark, oily, and full of depth! At this time, immediately take out the photo paper and throw it into the pool to stop toning.

3. Classic vulcanized double liquid browning toning (Sepia Toning) classical retro formula

Presenting the extremely warm, nostalgic and elegant pure warm brown golden tone of the 19th century Victorian era:

1. Step 1: Potassium Ferricyanide Bleach Bath:

• Recipe: Potassium ferricyanide (red blood salt) 30g + potassium bromide 10g + water 1000ml;
• Immerse the photo paper in the bleach solution: the black metallic silver is quickly oxidized into a milky white silver bromide latent image. The black and white photo gradually fades and disappears like melting snow within 1 to 2 minutes, leaving only a faint yellow outline; take it out and rinse it under running water for 3 minutes.

2. Step 2: Sulfide Toning Bath:

• Recipe: Sodium Sulfide 20g + water 1000ml (has a strong smell of rotten eggs and must be operated in a well-ventilated area);
• Slide the bleached photo paper into the vulcanizing solution;
• Visual Magic Explosion: The image that originally disappeared reappeared at an astonishing speed within 5 seconds, and was directly solidified into an extremely pure, warm, and historical warm Sepia Brown (Sepia Brown)!

3. Ultimate desulphurization and water washing:

• Neutralize by immersing in hypo-cleaning solution for 5 minutes, then washing thoroughly in running cold water for 30 minutes, drying and flattening.

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