Fixation - Teichaku

In silver halide photography, this is the process of removing unexposed or undeveloped silver halide after development, turning it into a photographic image that is stable to white light. Sodium thiosulfate is usually used as a fixing agent, and acetic acid or alum is also added to harden the gelatin to create the fixing solution. Sodium thiosulfate forms a compound with silver halide with the composition Na _x Ag _y (S ₂ O ₃ ) _{( x + y )/2} . Of these, those with x = 3, y = 1 and those with x = 5, y = 1 are stable complex compounds that are water-soluble. Fixers with 25% or less sodium thiosulfate often produce x = 3, y = 1, while those with 50% or more often produce x = 5, y = 1. The process of stabilizing exposed or developed images is also called fixing in photographic methods other than silver halide. Fixing in electrophotography often involves fusing the powder image to the support with heat. In wet development, the image is usually stable without any special processing. Other photographic methods involve the destruction or volatilization of the photosensitive components.

Source: Morikita Publishing "Chemical Dictionary (2nd Edition)" Information about the Chemical Dictionary 2nd Edition

ハロゲン化銀写真において，現像後未露光または未現像のハロゲン化銀を除去し，白色光に対して安定な写真像にかえる操作をいう．定着剤としては，通常，チオ硫酸ナトリウムが使われ，そのほかゼラチンを硬化させるために酢酸やミョウバンを加えて定着液とする．チオ硫酸ナトリウムは，ハロゲン化銀とNa_xAg_y(S₂O₃)_(x＋y)/2の組成の化合物をつくる．このうち，x ＝ 3，y ＝ 1のものおよびx ＝ 5，y ＝ 1のものは安定な錯化合物で水溶性である．チオ硫酸ナトリウムが25％ 以下の定着液ではx ＝ 3，y ＝ 1，50％ 以上の定着液ではx ＝ 5，y ＝ 1のものが多く生じる．ハロゲン化銀以外の写真法でも感光または現像した画像を安定化する過程は定着とよばれる．電子写真の定着は粉末像を熱で支持体に融着することが多い．湿式現像では，通常，特別の操作なしで画像は安定である．そのほかの写真法では感光成分の破壊，揮発などの方法が採用される．

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