Precipitate in bleacher

Discussion in 'B&W: Film, Paper, Chemistry' started by Tofek, Mar 15, 2013.

  1. Tofek

    Tofek Member

    Messages:
    70
    Joined:
    Nov 8, 2010
    Location:
    Paris
    Shooter:
    Multi Format
    Hello,
    The bleach is used in reversal processing, it is 10g K2Cr2O7 with 24mL of pure H2SO4. I haven't processed much yet (some tests strips) but there is already some precipitate. Just for curiosity, does someone know what it is ? I guess Ag2SO4 ? It darkens with light.
    I once got some black crystals (looked like black rice), when the bleach was used four or five times : was this Ag solid or Ag2S ?

    Picture of precipitate : http://imageshack.us/photo/my-images/822/imagexegf.jpg/
    Picture of crystals : http://imageshack.us/photo/my-images/833/imagejryg.jpg/
     
  2. johnielvis

    johnielvis Member

    Messages:
    940
    Joined:
    May 21, 2010
    Shooter:
    Medium Format
    ahhhh--you are reusing the bleach--yes--first the stuff was white sludge, then after a few days, those silver crystals started to grow. I got the same thing. I assumed it was silver crystals but stopped wondering when i went to a one-shot process. I'd like to know for sure what those crystals are too--anybody?