While researching pyro developers, I ran across the following statement on a Flickr group dedicated to Pyro:

510-Pyro has the advantage that you can visually check for the optimal developing time after around 1/2 to 2/3 of the total developing time under red safe light - then the pyrogallole has de-sensitized the film so far.

  • Is there truth to this statement?
  • If so, would this be applicable to any other group of developers?
  • If so, what is actually going on here to make this possible (please get at least a bit technical with the answer)

And finally - even if true, what would be the point? I can't imagine that one could tell if a negative is optimally developed without a loupe and with only the dimness of a safelight. The only thing that I can speculate is if developing sheet film in trays - turning the safelight on may aid the rest of the development process (by being able to see)...but given that the whole process can be done in the dark anyway, is the gain of sight here really all that much worth the risk?

  • \$\begingroup\$ May be worth splitting some of your questions out on their own to avoid letting this one be overly broad - Answering it all in one-shot is hard, and less useful for people looking up Q&As later. [But now I'm likely going to spend my weekend researching developer mechanics...] \$\endgroup\$ Jul 5, 2019 at 20:10
  • \$\begingroup\$ @TheLuckless I think the bullet points are all one question...but the final ask could be another, separate question. But, I also think it's applicable here. If the community starts voting this as too broad, then I'll split it up. For now, I think it's alright. You and I both will be doing some developer research this weekend! \$\endgroup\$
    – OnBreak.
    Jul 5, 2019 at 23:28

1 Answer 1


Developing sheet film is indeed the point. A fairly common approach when using large format cameras was to record things like exposure and expected development for each exposure and then to develop appropriately for that sheet (or plate). Being able to develop at least partly by inspection can help this process.

I don't know whether people still do this: it really relies on processing a single sheet at a time, which is probably still common for 8x10 but is not now and perhaps never was common for, say 4x5.

Orthochromatic film, which is insensitive to red light, makes this easier: many early emulsions were orthochromatic (this is why many B/W films have names involving 'pan(chromatic)': this was a selling point at one time.

B/W prints are essentially always developed by inspection, of course, and paper is intentionally not red-sensitive. One of the great joys of printing is watching the image appear on the print.

  • 1
    \$\begingroup\$ Probably worth noting that develop-by-Inspection is more common with prints than film. However still very useful in film, especially when working with orthochromatic films that are already red-light safe at the start of development. - Using it on roll film is 'possible', but has little/questionable benefit, unlike when using it on individual (and larger) images. And to me trying it on roll film just sounds like a pain to bother with in the first place. \$\endgroup\$ Jul 5, 2019 at 20:20
  • \$\begingroup\$ @TheLuckless Yes, I've updated the answer. You're right about the questionable (or in fact total lack of) benefit for roll film. \$\endgroup\$
    – user82065
    Jul 6, 2019 at 19:10

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