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I have just mixed the D76 powder to create the concentrate.

And I stored it in a transparent plastic bottle.

I wonder if that's harmful; whether it may deteriorate because it's in contact with light.

  • This would be better as a broader question. (How to store developer) with possibly “how to deal with large containers and small volumes regarding air exposure” added in. – Hueco Jul 29 at 11:19
  • Do you mean concentrate or stock solution? I think the correct term for mixing from powdered form is a "stock" solution which can be used with or without dilution whereas a concentrate suggests that it must be diluted for use. Some developers do come concentrated in a liquid form sealed for shipping. – Stan Jul 29 at 17:48
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What you want is called an accordion bottle. These are opaque, plastic bottles shaped like a cylindrical bellows with a cap on one end.

To use it, you pour in the liquid to be stored, compress the bottle until the level rises to the top and then install the cap. This customizes the size of the bottle for exactly the amount of liquid in it and eliminates almost all of the space for air that could react with the contents.

  • Yes, these are what to use if you have them. – user82065 Jul 29 at 16:19
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    I see them as gimmicky. They do not last long in use. They are impossible to clean properly and should not be used with different developers without a risk of cross contamination. – Stan Jul 29 at 17:56
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    @Stan I don't know what qualifies as long-lasting for you, but I bought a set in the 1980s and used them for about a decade with no problems. Can't say I had contamination problems, either. – Blrfl Jul 29 at 18:52
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Keep it in a dark place: the transparency or otherwise of the container then does not matter. I keep my mixed chemistry in transparent containers in a cardboard box.

However air is generally a more serious problem: the bottle wants to be nearly full and well sealed.

  • +1 for air. My filled bottle of Rodinal lasted for weeks without much discolouration, but after developing, the residue changed from brown to blue in a mere two days – timvrhn Jul 29 at 11:47
  • @timvrhn What do you mean with 'residue'? Rodinal is a so called one-shot developer and the working solution should only be used once and immediately after mixing. Fresh Rodinal concentrate is almost colourless, will however very fast get a brown colour, which has no impact on the developing properties. Even in contact with air, Rodinal concentrate will keep for many years. – jarnbjo Jul 29 at 12:01
  • The leftover solution, I had mixed slightly more than I needed. – timvrhn Jul 29 at 12:02
  • @timvrhn: I'm not sure that working-strength Rodinal will keep, even if unused & sealed. However I could well be wrong about this. That might be an interesting question to ask in fact! – user82065 Jul 29 at 12:59
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    Using clear bottles stored in a dark space also means it is easier to clearly see what's going on in the bottle. - After it has been allowed to age for a day or so and fully mixed, it may be worth breaking the batch down into smaller bottles for easier use. [Very handy to be able to open a bottle, pour the whole thing out for use, and not be left with a partial bottle afterwards.] – TheLuckless Jul 29 at 16:14
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The best storage will be a brown of green glass filled to the top and capped with little or no air space above the liquid level. Glass is best because it is impervious to air and will not contribute contaminates to the stored solution. As you use the concentrate or stock solution, add clean marbles to maintain a minimum air to fluid junction.

Next best is squeezable plastic bottles designed for chemical storage. Next is most any plastic bottle.

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