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When you look at development times between B&W films the development times vary when the speed of the film varies. For example:

  1. Ilford FP4 Plus with HC-110 dilution B at 20 degrees takes about 9 minutes for development.
  2. Ilford HP5 Plus with HC-110 dilution B at 20 degrees takes about 5 minutes.

But the development times of Kodak Ektar 100, and Kodak Portra 400, using Arista C-41, at 39 degrees, are the same, 3:30 Mins. Or when you choose Tetenal C-41 it is 3:15 Mins.

Why is it that the color development times remain the same?

Edit: This applies to ECN-2 an E-6 as well. As mentioned by @timvrhn

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Colour processes, such as C41, are standardised. That means that no matter the stock, development specifications stay identical.

This is also the case for slide film development (currently E6), and motion picture colour negative development, ECN-2.

I am sure you can see the benefits of such standardisation. Labs that receive large quantities of diverse film stocks, do not need to sort out these rolls to develop them in separate batches (with the problems that would come with such a process), but can take any colour negative roll and develop it altogether.

You can now also see why black-and-white development is cumbersome for labs, and why many labs will charge more for BW development or will outright not do it at all.

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  • \$\begingroup\$ @timvrhm Thanks for that, I now understand why labs charge more for B&W. \$\endgroup\$
    – Bartha
    Sep 30, 2022 at 14:32
  • \$\begingroup\$ I am guessing similar, higher temperatures are also responsible for standard development times? \$\endgroup\$
    – Bartha
    Sep 30, 2022 at 14:33
  • \$\begingroup\$ I am not sure I follow your question. The whole process is standardised, from temperature to times to chemicals used \$\endgroup\$
    – timvrhn
    Oct 2, 2022 at 8:48
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    \$\begingroup\$ @Bartha It's not so much the higher temperatures per se as much as it is the tighter tolerance allowed from the specified temperature. Temperature variations can be greater for B&W film without affecting the results as much as a minor variation in temperature for color processes. \$\endgroup\$
    – Michael C
    Oct 3, 2022 at 16:59

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