By taking advantage of bright red safelighting suited to orthochromatic films, roll films could be manually 'see-sawed' up and down through developer in a shallow dish (and similarly through stop bath & fixer). This technique was still advised in the 1950s for those wishing to 'have a go' at processing (orthochromatic) films at home, without the expense of a developing tank.

Problems were magnified in the late 1920s when the Leica camera introduced the possibility of using lengths of 35mm film too long for see-saw dish developing (a standard 36exp is over 5ft i.e. 1.5m). Also, by the 1930s, increased film speeds and the availability of panchromatic emulsions prevented the use of red safelights. This meant that a new approach was required to (home) film development.

As regards the need of the amateur enthusiast seeking to process his 35mm films at home, the 'focal' Photo Guide No.46 (1956) by Percy W Harris contains a useful description of how ideas progressed. He writes:

"First of all the user (of 35mm) could use a horizontal glass drum round which the film was wound (emulsion side out), the underside of the drum rotating in a dish of developer. That was not a particularly efficient solution to the problem, so the developing tank was introduced.

'Apron' Spiral Loading Tanks
The first tank had a circular moulded plastic body with a light-tight lid. Inside was a plastic bobbin (reel) with plain end faces, between which could be wound a length of celluloid (called an 'apron'), the same width as the film. This apron had little projections on its edges so that when the photographic film was wound within it, the film was touched only by the projections.

As they touched only the perforated part of the film and not the picture itself, the developer had access to all the picture area. Once the loaded reel had been placed inside the light-tight tank in the darkroom, the whole thing could be brought out into normal lighting. The necessary chemicals were then poured in and out without exposing the film to light. This soon became the standard way to develop 35mm films."

Alongside is illustrated a 'Correx', one of the earliest tanks of this type. The illustration is taken from 'Amateur Photography', edited by Anthony Johnstone, 7th edition (revised) 1951.

Centre vs Peripheral Loading Spiral
A little later, another type of light-tight tank appeared. In this design, instead of the reel having plain ends, separated by the width of the apron, the reel ends were made with spiral grooves and no apron was required. To load the reel, the film is inserted into the beginning of the groove (or sometimes clipped to the central shaft of the spiral) and pushed in from the outermost groove of the spiral towards the centre, until the end of the film is reached (or wound into the spiral, starting from the groove centre - this design requires the film to be momentarily bent lengthwise as it is loaded, so as to reduce the film width and allow it to 'spring' into the spiral groove).

Which is better?
Loading the apron type of tank is quite easy, but the disadvantage is that it is rather a messy business taking the film out of a wet apron. The wet apron takes a long time to dry because you get water in the dimples. Also, at the loading stage you have to take special precautions to prevent the apron collecting dirt from the floor. On the other hand, spiral groove tanks can sometimes give trouble in loading by the 'push-in' method, when the film may stick before it is fully inserted.

Mr Harris then goes on to describe the 'recently introduced' self-loading spiral groove tanks with the the facility to contra-rotate the ends of the spiral reel through part of a turn. He mentions that some self-loading spiral reels have a ratchet arrangement to assist the film along the groove (the Paterson patent) while others have no ratchet but are loaded in the same way by using alternate thumbs to hold the edge of the film as the reel ends are rotated one way and then the other.

Daylight Loading Developing Tanks
Finally, he mentions how some people found using a darkroom, even just to load their developing tank, was inconvenient and a demand arose for tanks which could be loaded completely in the daylight. A range of such tanks were made in Austria and imported by The Norse Trading Co. (London) Ltd. The Superkino took 35mm film, the Simplex took 120/620 roll film and the Super-Junoplex took 127 roll film. They were advertised on p653 of the BJPA for 1937. The exposed film was placed in the tank's side chamber and means was provided by which the film could then be wound onto a grooved spiral within the main tank body, while the tank and photographer remained in daylight. For more information on the Simplex tank, click here.

It seems the pre-WW2 Austrian manufacturer of the above tank range still manufactured and exported to the UK after the War, but with Photax (London) Ltd. as the distributors. The illustration, right, is from a November 1952 issue of Amateur Photographer magazine.

The darkroom loading tanks incorporated automatic up-and-down movement of the spiral during development by the simple expedient of shaped projections on the underside of the centre column of the spiral acting as cams to lift and drop the spiral as it rotated during agitation. This idea, or similar, became near universally applied around this time. However, it wasn't a new idea; the Kinofilmtank (peripheral loading spiral design for 35mm film) had this arrangement when tested by 'The Miniature Camera Magazine' in October 1937.

The daylight loading Superflex seems the equivalent of the earlier Superkino. The difference is that the post-War Superflex incorporated a 'cutter' to cut off exposed lengths of 35mm film, leaving the unexposed portion still in the cassette for later use.

The Dayight Loading developing tanks shown here were produced in the early 1950s as part of an ongoing co-operation between Johnsons of Hendon and Neville Brown & Co Ltd (Nebro).

The 'Essex' 35mm (left) was based upon the pre-War German Agfa Rondinax U35 design. The improved UK version was priced at £4.18s.6d (£4.93). The original Agfa instruction book is downloadable as a pdf file here, courtesy of Richard Urmonas.

While looking at the more unusual developing tank designs, the one shown left is another from Austria and is a novel way of incorporating multiple spirals into a single enclosure enabling simultaneous development of films. Instead of a tall tank, taking multiple spirals one above the other, the Tribox is a horizontal design with three spirals linked by a central geared spindle, such that all 3 spirals rotate together for agitation. The disadvantage of this design is that one cannot choose to develop just one film and use the developer quantity to cover just one spiral. The developer volume is fixed regardless of how many spirals are in use.

It emptied through a novel valve in the bottom, controlled by a spring-loaded shaft. A single nut served to lock both the valve and the tank lid.

The 'Tribox' advert (far left) claims that up to 6 35mm films can be processed 'back to back', 2 on each of the 3 spirals. Whether this means 2 off 20exposure 35mm films inserted one after the other, end to end, or really does mean 2 off 36exposure films, 'back to back', isn't clear. If the latter, this is an unusual claim which other manufacturers were reluctant to advise. As can be seen, the price, in September 1952, was £3.17s.6d (£3.88). An electric powered agitator cost £18.

Two other tanks, of conventional but unexciting design, branded by famous manufacturers, Ilford Ltd (left) and Gnome Photographic (right).

I owned a Gnome Universal tank in the late 1950s when my local chemist sold me an old one he still had in stock when I couldn't afford a more modern design e.g. by Johnsons, Nebro and Paterson, that had emerged by then.

The earliest GB patent relating to spiral loaded developing tanks seems to be GB320,716 with an Application Date of 20th August 1928 and a final completion date of 24th October 1929. It was filed by CLAYTON LYMAN DREW, a citizen of the United States of America, of 582, Market Street San Francisco, California, USA. The patent description includes the statement:
"The general object of this invention is to provide means whereby photographic negatives, for instance a strip of film, may be effectively developed, fixed and washed without any danger of scratching the surface of the film, and to provide means whereby a film may be wound upon a reel in such a manner as to maintain the various convolutions separated one from another.

The invention consists in apparatus for the treatment of photographic negative films comprising a container and a reel shaped member adapted to be removably positioned within said container and between the top and bottom portions of which the film to be treated is held, characterised in this that the bottom member of the reel is provided with an annular downwardly extending peripheral flange resting on the bottom of the container and both top and bottom members are provided with openings so arranged as to enable the fluid entering the space bounded by the bottom member, the flange thereon and the bottom of the container, to flow freely upwardly over the surface of the film."

DONALD MACDOUGAL PATERSON is the named inventor on 30 patents relating to photographic equipment, published between 21st November 1951 and 6th September 1977. The full list can be seen here on the European Patent Office web site (esp@cenet).

The earliest of Donald Paterson's patents relate to the inclusion of his famous 'ratchet action' to facilitate easier loading of film into the already well established film spiral used in photographic developing tanks. This patent, GB661,288, was published on 21st November 1951, but the original Application Date was "15th day of December, 1948". In this earliest patent, Donald Paterson describes the now familiar arrangement consisting of "a pair of spiral grooved plates, but instead of being rigidly fixed together the plates are arranged so that they can move independently on their common axis." However, this initial patent describes the ratchet loading of film into the spiral as being assisted by "a series of projections or teeth attached at intervals along the grooves." Although these teeth are described as "hinged or fixed, or moulded into the grooves or attached separately", there is no mention of the eventual use of ball-bearings working on inclines and held captive within small chambers at the entry of each spiral.

Interestingly, it is the GENERAL ANILINE & FILM CORPORATION who, in a patent with an original Application Date of 7th February 1948 (albeit in the USA), first make mention of the ball bearing arrangement. Their 'bibliographic data' describes a "spiral groove, of which the outer groove wall is thickened and is formed on the inside with a recess containing a ball. When a film fed through openings into the groove passes (the) recess, the ball is moved into a larger part of the recess and permits the film to move into the spool. Should the film move in the opposite direction, (the) ball is moved into the narrower end of the recess and jams the film edge against the next groove wall. By relative movement of the discs in alternate directions, the film is moved step by step into the spool." This invention was filed as a GB patent (664,162) on 21st January 1949 and was published on 2nd January 1952. Thus, although the original filing of this patent (in the US) pre-dates the first from Donald Paterson, Donald's patent was published first.

Donald Paterson's patent, GB661,356, "divided out of 661,288" has the same Application Date and Complete Specification Published Date as GB661,288 (above). This papent describes "A spool for receiving photographic film for treatment in a processing tank, comprises a pair of spaced coaxial plates rotatable relatively to one another about their common axis and each having on its inner face a spiral track defined by upstanding walls, said tracks having either their outer or their inner ends open for the insertion of the leading end of a film, and, located in at least one track, a captive roller working on an inclined plane forming one wall of the track, the upper end of the incline being towards the entry end of the track and the gap between such upper end of the incline and the opposite wall of the track being less than the diameter of the roller. Apart from the captive roller and the inclined plane, the spool is identical with that disclosed in Specification 661,288." The patent bibilography also states "Reference has been directed by the Controller to Specification 664,162." With only a lay understanding of patent law, I cannot claim to understand what legal point is made by the above "Reference by the Controller", but from a practical viewpoint it appears that the idea to use contra-rotating spiral ends together with some form of ratchet device to encourage the film along the spiral grooves, was invented almost simulataneously on both sides of the Atlantic.

Alan Meek, Technical Manager of Paterson Products until 1981, e-mailed (March 2007) to say the near simultaneous invention of the self-loading film spiral in the UK and the US was genuinely a coincidence.

"Paterson's tank at the time was for 35mm only and the film holder was referred to as a "spiral". As the backward-pointing teeth would only engage in the sprocket holes of 35mm film (Donald) Paterson wanted to create a spiral for roll film too and he came up with the idea of a ball-bearing in an inclined track. The track was a tiny moulding which was glued into the side of the spiral. As the side of the spiral was pushed forward the ball-bearing was forced into the narrow end of the incline and so gripped the film, to push it forward. When the side was spun the other way the ball-bearing moved into the wide end and released the film so that it could slide past.

Ansco (General Aniline) in the USA happened upon the same idea at essentially the same time. Their patent held sway in the USA so for the next 16 years Paterson couldn't sell their tank there, while ANSCO had no access to UK markets. After that time Paterson did begin to sell into the USA, changing the word "spiral" to "reel", since the latter word was more intelligible to the Americans.

Interestingly, Paterson used "reel" for its markets worldwide from then on, because it was more convenient to have just one package and instruction for all english-speaking markets. They changed from referring to "developing dishes" to "developing trays" at the same time and for the same reason."