I have a Paterson Universal Tank for developing film. It's written underneath that for 35mm we need 290ml to fill.

I plan to put in 500ml into it. Simply because it's easier to make the solution.

I see that the tank can hold up to 600ml-700ml.

Will it affect the final result of development if I do so? Or should I strictly follow Paterson instruction 290ml?

  • Were you aware that the photographic industry has some of the most virulent chemicals (read pollution, contamination)? Rather than take the lazy way for a hobby that destroys the environment it loves to capture artistically, why not shelve convenience in favour of responsible planet husbandry? Mix exactly what you need for use. Do not make more than you require for the job.
    – Stan
    Jul 19, 2019 at 22:48
  • 1
    @Stan What you say about "planet husbandry" is reasonable for one-time-use chemicals, but for those that are reused, it usually doesn't matter much. In some cases, mixing a bit more can be more environmentally friendly. For instance, mixing an amount that completely fills the storage containers reduces free air and oxidation, which prolongs the life of the chemicals. Some people use canned air to displace the oxygen, but the chemicals used to produce canned air are not environmentally neutral.
    – xiota
    Jul 20, 2019 at 6:59

4 Answers 4


Provided your Paterson tank is of type 115 - the one that can take either two 135 or one 120 films - it is the best practice to fill it with 500 ml (or so... can be up to 520 if using Rodinal 1+25 dilution) of developer.

You can load the second reel empty, to ensure uniform cover or your film.

For most developing situations this is merely a convenience issue, but if you plan to do stand development with heavily diluted Rodinal (say 1+100) you could have real problem with 290 ml only (2.9 ml of stock Rodinal is not enough to ensure even development).

  • "it is the best practice to fill it with 500 ml" – I don't disagree with you, but the instructions that came with the tank appear to contradict this statement. Can you explain where this "best practice" comes from?
    – xiota
    Jul 19, 2019 at 15:38
  • 1
    @xiota I did not mean that using 290 ml would be wrong (it is not) but rather that it is inconvenient, and usually not worth the hassle. It is much easier to prepare 500 ml of developer, especially when using one shot liquid ones, than 290. The "savings" of using only 60% of chemicals compared to 500 ml are usually negligible. The only exception I know of is stand Rodinal, which is at best a marginal practice - some people swear by it, others (e.g. me) don't have the patience for it. Jul 19, 2019 at 17:07
  • I wasn't disagreeing with your recommendation to use 500mL. I was questioning your claim that it is "best practice". I fill the tank for convenience.
    – xiota
    Jul 20, 2019 at 0:32

Developing film is a combination of chemical processes. These processes utilize an interaction between the film and a chemical dissolved in a solution.

What do you think happens if there is too little of a chemical for the needed reaction? That's simple: the reaction stops.

Just about everything in the film developing process is based on providing the reaction more chemical than is actually needed and controlling for the reaction through time and temperature.

Development: In developing, 99% of developing is done with an abundance of developer chemical and the total development reaction controlled by temperature and time. This is why you make 1+X of your developer and develop at (usually) 20C/68F for Y minutes (whatever your developer tells you).

You need to make enough developer to cover the film, which is a function of volume. Anything extra is there for padding. What you want to avoid is streaky negatives. This can occur when there is too little developer (volume) and it runs down the partially submerged film. The film can become partially submerged through agitation when not enough fluid is used.

So, your Patterson tank says to use a minimum of 290mL - anything you add is extra padding on this. If the math works out easier to make 500mL, then do it. Keep in mind that this is using up more of your developer than necessary, but it doesn't hurt (except maybe your wallet).

Developer Exception to the Rule: When doing stand development with Rodinal, developing the chemical to exhaustion is the goal. One typically uses 1+50 or 1+100 (or even more dilution) and lets the film "soup" in it for an hour (or more). Rodinal recommends using no less than 5mL of developer (I've seen people say less. This is a highly experimental practice). But, keeping in mind that 5mL is used per 35mm roll, then your minimum volume is 500mL and you'll need to use every.last.drop to get results.

Stop Bath: I don't even measure this. Pour from the jug until the tank is full. Return to jug when done.

Fix/PermaWash: Again, the exact volume doesn't matter as the idea is that the chemical has plenty to react. Pour to cover plus a little extra to ensure proper submersion during agitation.

Photo Flow: Yep, same thing here. Although using any more than enough to cover the film is simply wasteful at this step.


Take the top off of the tank, put in the real/reals and fill with water until the top of the real/reals are covered with water.

Pour the the water into a measuring vessel and then read how much liquid it took to cover the real/reals.

Write the amount down for one real and for two reals ( or more if it holds them ) and pin it to your darkroom wall over your sinks.

You may want to round it up to a nice round number ( metric ) for ease of mixing.

Now you can figure out your amount for mixing the different amounts for any number of reals then post those formulas on the wall.

  • 1
    Real - genuine, true, actual, non-fiction. Reel - a cylinder on which flexible materials can be wound. You have a real problem with reels, I think. An edit can fix this however.
    – Stan
    Jul 19, 2019 at 22:36

Agitation with Paterson tanks is done by spinning the reel, so it's only necessary to cover the film. Other systems, where agitation may be by inversion or other means, require the tank to be nearly full (some air is required).

The necessary chemical reactions occur based on concentration and time. Having more or less solution in the tank won't affect results, as long as the film is adequately covered. For convenience, it's fine to just fill the tank to capacity.

Using low volumes of low-concentration solutions can result in developer being exhausted prior to the full development of the film. The problem is developer is exhausted and concentration essentially drops to zero midway through development. To avoid this issue, you can use higher concentrations or larger volumes to prevent the concentration from dropping too low. These can be characterized within a recommendation to use a minimum amount of developer, prior to mixing. (Using more developer without increasing volume increases concentration; while using more developer, with the same concentration, increases volume.)

  • 'The necessary chemical reactions occur based on concentration and time. ' This is incorrect. For all developers, you need a minimum amount of active agent to develop a film and especially at higher dilutions, you may need a larger amount of working solution than just to cover the film. The number is exaggerated, but it is for example often claimed that you need 10ml Rodinal concentrate per film, which at a 1+50 dilution means 510ml working solution per film, or about twice the amount needed to cover a 135 film in most developing tanks.
    – jarnbjo
    Jul 19, 2019 at 15:15
  • @jarnbjo You're describing an edge case in which the concentration of developer in solution effectively drops to zero midway through development, which is a concentration issue. With standard concentrations, the change is small enough that it can be ignored and overall concentration treated as constant.
    – xiota
    Jul 19, 2019 at 15:18
  • No, I am not. 1+50 is a normal dilution for Rodinal and that was just one example. You can run into the same problem with other developers as well. For ID-11 or Microphen in 1+3 dilution, you need 400ml working solution per film. For Perceptol 1+3, you need 800ml. All according to the data sheets from Ilford.
    – jarnbjo
    Jul 19, 2019 at 15:25
  • "Agitation with Paterson tanks is done by spinning the reel" -- or, by using the (not that great) lid and doing inversions. That being said, I've never had a lid easily fit and seal on a Paterson tank...
    – OnBreak.
    Jul 19, 2019 at 17:47

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