Variables in residual Thiosulphate testing

Discussion in 'B&W: Film, Paper, Chemistry' started by Tom Kershaw, Mar 3, 2009.

  1. Tom Kershaw

    Tom Kershaw Subscriber
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    Having just tested a sheet of Kentmere Kentona for residual Thiosulphate, I realise there is a potentially significant variable in terms of how long the paper resides in the print washer before a continuous flow of water is applied. After a 45 minute wash, the paper passed according to the comparison wedges printed in 'Way Beyond Monochrome'.

    However, when after placing the fixed paper into the washer I turned the wash on almost immediately, whereas in a practical printing session I might load the washer with 8 to 10 prints over the course of three hours and then turn on the water flow; with each print bringing new thiosulphate into the washer. So my question is to what extent a variable soak time will alter print washing efficiency and effectiveness? To some extent this can be experimented with but there will still be random variables.

    Tom.
     
  2. ic-racer

    ic-racer Member

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    You should test under your practical operating conditions.

    In general, whenever the concentration of fixer in the paper is more than the concentration in the water, it will be 'washing' the paper. Whenever the concentration of fixer in the water exceeds that of the paper, it will be 'contaminating' the paper.
     
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