Choosing a developing tank

There are two kinds of developing tank: plastic, and stainless. The differences go a lot further than the materials of which they are made.

Stainless steel tanks normally take stainless steel reels (spirals) in various fixed sizes, and have push-on stainless steel or plastic lids. The reels are normally loaded from the centre outwards. Plastic tanks normally have screw-on lids and take adjustable plastic reels, usually just 35mm/126 (both 35mm wide) and 120/220/620 (62mm wide), though some can also be adjusted for 127 (46mm wide) or 16mm or both. Plastic reels are normally loaded from the outside inwards, either by some form of ratchet action or by simply pushing the film in. As a general rule, if a tank will take one 120 or 220 spiral, it will take two 35mm spirals.

Stainless (left) and plastic (right) tanks


s/s tank


By comparing the sizes of the 35mm spirals, you can see that these two tanks are not reproduced on the same scale, and you can see that the stainless tank (Kindermann) has only four parts -- cap, light-trapped top, reel, tank -- as compared with the plastic one (Paterson) with its cap, central spindle (for 'twirl' agitation), light-trapped top, reel, core, and tank.

Stainless steel tanks often need less chemistry per film, except for those plastic reels where you can load two 120 films end-to-end on a single reel, where plastic has the advantage. Stainless tanks are often less likely to drip when inverted -- though inversion agitation is far from essential. Stainless tanks also have less thermal capacity, so if the temperature of the tank is widely different from the processing temperature, it will affect the temperature of the processing solutions less.


Both types of tank are light-trapped so that the film can be processed in normal room lighting, once it has been loaded in complete darkness, and both are available in various sizes from single-reel upwards. Depending on the design, anything that requires more than about 450ml/16 oz of chemistry may take too long to fill and empty: this sets a limit of one 120/220 spiral or two 35mm spirals. Plastic tanks often fill and drain faster, which can be especially important with multiple reels (the stainless tank merely has a deeper tank; the plastic tank needs a different core).


paterson tank

Plastic reels must be bone-dry or the film will stick; as long as stainless steel is wiped dry, that is enough, which is one reason why stainless is favoured by professional labs. Plastic reels often bounce better when dropped on a hard surface -- stainless steel can bend, or even come apart at the welds -- but cheap stainless steel reels are a lot easier to damage than expensive ones. Cheap spirals are sometimes a little skimpy and may only just take a full 35mm film plus leader; with cheap ones, you may need to cut off the first two inches (5cm) or so of the film after the leader.

Reputedly, wetting solutions can build up on plastic reels, and certainly, some can become rough and sticky with use: an undamaged stainless reel should last forever. Most stainless steel reels can be interchanged in most stainless steel tanks; plastic reels are normally limited to the type of tank for which they were designed. Most plastic 120 reels will also take 220; with stainless steel, it is more usual to have separate 120 and 220 reels.

Neither plastic nor stainless is inherently superior. If they were, one of them would have died out. Mostly, preferences come down to which is easier to load, and this in turn is likely to come down to which you started with. We generally prefer stainless steel for 35mm (Kindermann with Hewes reels) and plastic (Jobo) for 120, both for ease of loading and economy of solutions.

Kindermann (left) and Paterson (right) tanks

The difference in tank size is clear here, as are the different styles of reels. Both take two 35mm spirals or one for roll-film. The larger spiral for the Kindermann is for 120: a different spiral, with more turns, is needed for 220. Obviously a 220 spool can be used for 120 but it is more expensive and slightly harder to use.

The spirals for the Paterson can be adjusted for either 35mm or 120. Twist them to the limit of their travel (the two ends rotate relative to one another) and pull. If they separate completely, don't worry: just push them back together and twist again so that they lock in the closed position (35mm) or the wider-apart position (120/220). If they don't pull apart, you're probably at the wrong end of the travel. Look at the grooves in the inner part and you should be able to see quite clearly how they come apart and fit together.

two tanks

Second-hand tanks and spirals

A good-quality tank will last half way to forever, but there are things to watch out for with second-hand tanks. Light leaks are rare, but not impossible, especially with plastic tanks. Fluid leakage, when inverted, may be a result of poor design or manufacture or simple wear and tear. Stainless tanks with plastic lids are the most likely to start out leakproof and stay that way. Stainless tanks with stainless lids can often be rendered a lot more watertight by slipping a broad rubber band around the joint between tank and lid: an old motorcycle inner-tube will provide a lifetime's supply.

Mechanical damage (bent wires, broken welds) is usually easy to spot with stainless spirals and is cause for rejection: they are not worth trying to repair. Stickiness with plastic spirals can be harder to spot: testing with a scrap film is always a good idea. White plastic spirals do stain, but this does not necessarily affect their performance. Use an old toothbrosh to remove black (silver) stains, but don't expect them to come up like new.

Note that some plastic tanks (such as Jobo and newer Patersons) require separate cores to support the spirals while others (such as older Paterson) do not. Tanks used without cores are not usually light-tight so make sure you get the cores if you buy second-hand tanks.

Loading spirals

Loading 120 spirals (both stainess steel and plastic) is covered in the free Basics model on handling 120 film. Loading 35mm into spirals is covered in the free Basics module on loading 35mm into developing tanks.

The illustrations above are taken from our Darkroom Basics -- And Beyond.

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© 2007 Roger W. Hicks