ORIGINAL TINTING AND TONING TECHNIQUES AND THEIR ADAPTATION FOR THE RESTORATION OF ARCHIVE FILM.

By Paul Read

SUMMARY

The Archive Film Restoration Department at Soho Images offers a service to prepare restorations of coloured nitrate film using and the original tinting and toning techniques on modern print film stocks. The images are closer to the originals in their pristine condition than any reproduction on modern colour film. Our interest was stimulated by the seminar at the Nederlands Filmmuseum in July 1995 when we recognised that, although a few experiments had been carried out, only a few tinted and toned films had been restored using the original tinting and toning formulae since the procedures ceased to be used commercially about 1930.

This paper looks at the original techniques used for tinting and toning and the adaptation of data from the literature of the period to modern restoration.

1 PART 1 - ORIGINAL TINTING AND TONING PRACTICE

1.1 INTRODUCTION

Tinting is the process of colouring the silver print image overall with a dye in the emulsion or the film base or by applying a coloured "lacquer". Stencilling and hand colouring was the process of locally applying tint dyes to the silver image. Toning is the process of replacing the silver image with a coloured image material.

We have only seen reference to the lacquering process mentioned above in the Agfa technical process manual of about 1925. This indicates the use of "lac" dyes in a varnish-like solvent applied over the picture area between the perforations to create a tint. This coloured stripe would be very easy to identify, but we have never seen an example nor did the Nederlands Filmmuseum survey of their own collection reveal any. We have made no attempt to reproduce this technique.

Hand coloured and stencilled films were produced by locally colouring a black and white positive print. Some of the prints were presumably made slightly light in density but the techniques and the dyes used to dye the film were the same as for tinting, except for the local application. A number of stencilled films were made on tinted film base or seem to have been tinted overall as well, usually pale yellow.

1.2 TECHNOLOGY OF COLOURED NITRATE FILM

By the time cinema commenced in 1896, photography was many decades old and a wide range of techniques for colouring the neutral silver images had been tried out on paper prints, and more importantly for cine film, on glass lantern slides.

Some of the earliest experiments used natural dyes such as logwood [reddish brown], madder [red] indigo [blue] and turmeric [yellow] to dye gelatine, paper or the silver images. By the time cinematography existed a number of proven, ready made, techniques using synthetic dyes already existed. There is surprisingly little early technical literature on the methods used to colour film and although it seems likely that hand colouring and stencils came before overall tinting and toning, which was a cheaper alternative, tinting lantern slides was described in several still manuals of the 1880’s.

1.2.1 Metallic toning

Image silver is neutral in colour and all it’s salts are white or more or less neutral to transmitted light. However other metal salts can replace the silver of the image. If these salts are coloured, insoluble and relatively transparent [generally in the form of a colloid] the neutral image can be replaced by a coloured one.

Toning processes using metal ferrocyanides were known to photographers well before motion pictures. The Iron Tone Blue or Iron Blue process was known as Cyanotype to photographers and used on paper from the 1860’s. Several techniques used on paper are unsatisfactory on film as the resulting dye is not transparent and is seen as black when projected [although it may be highly coloured by reflected light [e.g. sulphide, selenium and gold toning].

The following metal salts were widely mentioned for metallic toning cine film:

Ferric ferrocyanide [Prussian Blue] - blue, blue green or olive green

Uranium ferrocyanide - orange red, red or red-brown

Copper ferrocyanide - red or reddish brown

Vanadium ferrocyanide - yellow, yellow brown, or olive green

Silver sulphide - blue-black to brown [the traditional reddish brown of still photographs is only produced from very "thin" images, as sulphides are opaque]

Sepia, as seen on old paper prints, is silver sulphide, and is red-brown by reflected light. This colour was desirable on cinema film but silver sulphide is almost completely opaque and therefore projects as a neutral or blue-black image. The most usually mentioned "sepia" colour was achieved by creating a mixture of ferric and uranium ferrocyanides, and an olive green was produced by mixing vanadium and uranium ferrocyanides.]

The process usually comprised a single toning bath of potassium ferricyanide [the silver bleach] and a metal salt. "Fixing" if it was done was a separate solution, probably a conventional black and white fix bath, sodium thiosulphate [see below].

The chemistry of these reactions was not well known until the 1930’s, well after toning ceased to be important in this respect. Many of the early toning procedures were more akin to cookery than chemistry!

[In the 1920’s and 1930’s a lot of research and development went into Prussian blue and Uranium ferrocyanide toning in order to produce "perfect" two-colour primaries that were complimentary, for use in the various duplitized positive two-colour films such as Cinecolor, Trucolor, and Dascolour etc]

By the mid 1920’s it is possible that the only widely used metallic tone was Iron Blue [Prussian Blue]. Uranium was expensive and toxic, copper recipes often damaged the film emulsion, vanadium was only available as a messy concentrated impure "syrup", and all were a little unpredictable. Several papers, as early as Reid 1917 indicate that mordant dye toning could do everything metallic toning could do but better. However Iron Blue certainly continued, probably as it produced such a unique amazing blue colour. Apparently there were no strong blue mordant dyes at that time.

Several papers and "recipe books" indicate that the residual salts in the image, usually white silver ferricyanide and/or metallic silver could be removed by "fixing" or "clearing", using an acid sodium thiosuphate solution [a fixing bath]. The chemical process here is a little uncertain, but the result is a bright clear translucent image of high saturation. This image is recognisable from the pristine unprojected sample books from Gevaert and Pathe. [Prussian blue fades in the projector-sometimes almost the entire image vanishes except at the frame corners- and it also ages by darkening and becoming desaturated, more neutral.]

1.2.2 Synthetic dyes for tinting

The earliest photographic processes existed before the discovery of the first artificial dye [Mauveine] by Perkin [by mistake] in England in 1856. By 1896, man-made dyes were being discovered [or invented] at a tremendous rate. The early development was in England, later Germany, France and then USA developed considerable numbers, and by 1910 the USA was the largest producer. These dyes originated from complex organic chemicals in coal, oil and tars and were not of just a single type. No doubt hundreds were tested on film [about 5,500 dye chemicals of this type are known today], but many were quite unsuitable. Some dyes are inflammable, explosives or toxic, and some of the intermediate chemicals are equally dangerous [Perkin blew up two factories during his lifetime!]. Others were found to cause rapid and permanent damage to film emulsions, resulting in the first use of the term "brittleness" in photography [the emulsion cracked and peeled off the base]. Frothing of the dye solution also seems to have been a common problem.

By about 1920 Eastman, Gevaert and Pathe were recommending specific dyes, but presumably some very unsuitable ones had been in use at earlier times. Most dyes were selected for their solubility in water, and many were originally used in dyeing wool, like gelatine a protein. Most of the most suitable dyes have stood the test of time and are still available today.

All dyes fade [either decolourise, darken or change hue] in time and in certain conditions of temperature, humidity and UV irradiation, but surprisingly little information exists as to which dyes fade in which way, creating a major problem for those of us who wish to identify and re-use the original dyes for restoration.

These synthetic dyes useful in photography fall into two broad categories, "acid dyes" generally available as a sodium salt which are mostly used for tinting [and "basic dyes" that can be mordanted to the substrate are used for mordant dye toning - see below].

A typical tinting process consisted of soaking the black and white print film in an aqueous solution of dye [from 0.5 - 20g per litre] acidified with acetic acid. The film was then washed in water to remove excess dye.

Many of the English and American papers refer to "Cine" Red, Green, Light Green, Blue and so on. This loose term presumably originated with Eastman Kodak, but other authors use the same terms often referring to other dyes.

1.2.3 Mordant dye toning

A mordant is a chemical to which a dye bonds, loosely or intimately, and if the mordant is in the emulsion in the form of an image, a dye image is produced. Photographic silver is not a mordant for dyes, but some of the salts of silver are; likewise some related metal salts are mordants and can replace the silver. The most used mordants were

silver iodide

silver ferricyanide, and silver ferrocyanide

uranium ferrocyanide

copper ferrocyanide.

Generally the mordants were retained in the film emulsion and some, like silver ferricyanide, were relatively translucent. In some processes the mordant was subsequently removed [by a "clearing bath"] to leave a "bright" or transparent highly saturated image, analogous to the "fixing" of Iron Blue. Some of the frames in the Gevaert and Pathe sample books we have seen, presumably that have never been projected, are dazzling and highly saturated.

A typical two stage mordant dye process consisted of a solution of "mordant bleach", usually acid potassium ferricyanide, with or without a halide, or another metal salt, to produce one of the mordants above as a replacement for the silver image, followed by an aqueous solution of a "basic" dye [usually about 1-5 g per litre].

Following the toning bath the film is washed to remove the excess toning dye from the emulsion. The length of this wash [and the temperature and pH of the wash water] can be critical, as the toning dye can be removed or reduced by a long wash. Similarly we have identified toned images with dye retained in non-image areas [like a tint of the same colour, easily achieved by reducing this wash time.

A "clearing" stage to remove the mordant is usually a conventional photographic fixer of sodium thiosulphate applied after the wash and followed by a further wash stage.

1.3 THE ORIGINAL LABORATORY TECHNIQUES

1.3.1 Processing

Most of the American laboratories from the earliest times until about 1920 carried out their conventional processing in batches of 200 ft of film wound round wooden cylinders called "drums" that just dipped in shallow trays of processing solution and were continuously rotated. Batch processing continued, at least in America, until about 1929. Drums, flat wooden "racks" holding 200 ft, submerged in deep tanks, and "pin racks", in which the film is wound in a concentric spiral, continued to be used. Presumably the same or similar equipment was used for both development and for tinting and toning.

Both Pathe and Gaumont experimented with "tube" processors, some of which were continuous and these may have been used for tinting and toning.

Continuous processors are mentioned in early patents and some literature but it is difficult to be certain where and when these were first used extensively.

1.3.2 Positive cutting or "Assembly"

Until about 1930 it is believed that many, or most, films were finally assembled as positives. In colloquial laboratory parlance they were "pos cut" and not cut as negatives, or "neg cut". In effect short single scenes were made up into small rolls, which were then printed in one printer pass for each roll onto lengths of print stock. The resulting short lengths of print were then "pos cut" to make the final print. Multiple copies were made by multiple positive cutting. Today, this would seem incredible and although literature of the time occasionally describe this, it is sometimes difficult for a modern film technician to accept.

Certainly not all films were treated this way and the British Pathe collection, just as an example, contains newsreels and magazine programmes, like Eve's Fim Review [1918 -1928 approx], in which each short story was a series of joined negatives, just like a modern cut negative. Presumably these programmes were never intended to be coloured. Some films, [e.g. "Blood and Sand" and "Cabiria"] were released with the same colour effect throughout, so these could have been "neg cut", but few processors could process continuously until the 1930’s. Undoubtedly most tinted and all toned material was "pos cut".

An interesting example which was not entirely "pos cut" is a section of "Bachanale"[1916?] in the Nederlands Filmmuseum which has several "fast cut" tinted sections where the colour changes at intervals throughout a scene. The colour sections are short and might correspond to a segment of a film rack about 40 cm or so in diameter. Different segments were dipped in different tinting solutions.

1.3.3 Pre-tinted film base

All tinted film was made by dipping the finished print into an aqueous solution of dye [sometimes called "post-tinting"], until about 1918, when "pre-tinted" base became available.

Pre-tinted film was sold until about 1930, and it might be expected that pre-tinted film very quickly replaced "post -tinting", However, an American laboratory textbook of 1927 and a French manual of 1926 both imply that laboratories at that time still tinted much of their own prints as a routine.

Pre-tinted base is more uniform than "post tinting" although not universally, and can be separated from post-tinting by scratching the emulsion off in an area outside the frame. If the film is pre-tinted, i.e. the base material dyed, or a layer of tinted material on the back of the film, the colour will not change. If the film is post-tinted the clear base shows through the scratch.

As an example, "The Pleasure Garden" [1925], is tinted throughout with nine colours. Probably two are pre-tints and six are post-tints. One strong blue tint dye exists as both pre-tint and post-tint [probably Patent Blue], as if the laboratory ran out of pre-tinted base during production! The "reel number" leaders and the "end of reel number " tails are also tinted.

In the catalogue of the chemical supply company Societe Anonyme des Matieres Colourant & Produits Chimiques de St Denis, France, apart from a list of dyes for tinting gelatine, there is also a list of dyes suitable for dyeing cellulose nitrate film base.

The paper by Lloyd Jones on the Eastman Kodak product Sonochrome lists all the 17 pre-tinted bases available in 1929 for printing sound prints. Some of the previous tint dyes had significant densities in the infrared and reduced the signal to noise ratio of optical sound tracks.

1.3.4 Toning

Toning was always done in the laboratory and was also difficult to do in long lengths.

Positive cutting must have been used for all toned material, as toning by the usual techniques can only be done after the print is made. Toning is often quite a fast chemical reaction and agitation was essential to achieve even results. We have found that the Iron Blue process is particularly critical.

A further complexity of Iron Blue was that the full colour could take some hours to develop, well after the film was dry and rolled up! This has made modern process control a problem, as we now have to wait six hours before establishing whether the process was on aim!

1.3.5 Double effects

Double effects, such as the common iron-tone blue and pink or yellow tint, would be most conveniently produced by using pre-tinted base film and toning the print, but most iron-tone blue and pink or yellow tint we have seen have both been produced in the laboratory.

"The Lodger" 1927, uses Iron Blue tone and amber tint for all the exterior scenes to produce a double effect, that simulates a London "particular" [a smog], in which the amber tint varies considerably in depth from scene to scene. Some film is pre-tinted, and some post-tinted, in both cases on Kodak film. The intertitles are on a different stock, Pathe; probably negative or "process" film, and these were all tinted in the laboratory to a denser and more orange colour.

2 PART 2 - ADAPTATION TO THE MODERN LABORATORY

2.1 INTRODUCTION

Hand coloured and stencilled prints have generally been preserved on colour internegative, but much of the tinted and toned material has not been preserved in colour. Most early coloured film is preserved in archives as black and white duplicate negatives and prints with just a written record of the colours. The image has good archival permanence but there is no visual record of the colours, either as faded by time, or as originally seen. Most archives carry out some colour reproductions for display purposes but all are prints on modern colour print stocks. The Nederlands Filmmuseum has copied large amounts of coloured film using Eastman Colour Internegative Film, and the Cinémathèque Royale de Belgiques has used the Desmetcolor method for many years. Noel Desmet’s method is now used by several European laboratories including Soho Images

"The Lodger" [1927] was restored by tinting and toning by Harold Brown at the National Film and Television Archive in 1984, and this was also the first film Soho Images restored by this technique. The original print had the clear blue images easily recognisable as Iron Blue. These seem to have darkened but were still more "transparent" than any Iron Blue we could produce until we used the "fixing" technique.

Showing "The Lodger" has produced some startled reactions from normally staid archivists. The tradition of copying the colours of tinted and toned films as they are today, in their tired and faded state, may not have prepared us for the original unfaded dyes.

The methods that could be, or are being used, for colour restoration are:

2.1.1 Colour Internegative

An Eastman Colour Internegative can be produced from the original coloured prints, using flashing to reduce the contrast if necessary.

This film was originally designed for making internegatives from the 16 mm low contrast reversal camera original film, Ektachrome Commercial. Some laboratories use a camera negative film for this purposes they are particularly successful in reproducing some rose pinks and pastel oranges.

The principle problem with this method even if the film stock was perfectly designed for this purpose is that the resulting print is a copy of the faded colours left on the original nitrate material.

2.1.2 Direct Colour printing

Various printing techniques use the black and white duplicate negative printed onto colour film print stock. "Desmetcolor" [Noel Desmet, Cinématèque Royale de Belgiques] is capable of excellent results and reproduces the visual effect of both tinting and toning over an enormous colour range. This method is capable of simulating complex tint and tone combinations, and the only limitation is probably the range of colour saturation available with subtractive primaries. [See paper in this Journal]

[Some laboratories simply print the black and white duplicate negative directly onto colour print stock and grade to a coloured image. This is a satisfactory simulation only of certain mordant dye tones, especially where the silver image has been "fixed" out].

The principle problem with this technique is that of deciding whether to copy the colour of the probably faded old print, or to create the colour of the original unfaded dye.

2.1.3 Digital restoration

Scanning of the image, either an original coloured print or a monochrome duplicate negative, to digital electronic signals and their manipulation to give a visual image that resembles an early tinted and/or toned result, followed by the transfer of the signal back to 35 mm colour negative film in a film recorder. A colour print is then made from the negative. This has been tested but not used by an archive.

2.1.4 Tinting and toning a modern black and white print

If the dyes and chemistry are the same as originally used in the first three decades of this century the results should be closer to the original than any other method.

Original Coloured Image - Panchromatic B/W Negative - B/W Print

OR

Any Duplicate Negative - B/W Print

The final B/W print is then tinted or toned using original chemistry.

There has been some discussion, especially internally in Soho Images, as to whether a print for tinting and toning should be a special density or contrast for the tinting and toning procedure it will receive. Some literature especially for metallic toning does suggest thinner prints than normal but, in general, we have found that a good B/W print makes a good tinted or toned result.

This paper describes these processes

2.2 GENERAL PROBLEMS IN RESTORATION

The principle problems, which apply to all these restoration techniques, are:

2.2.1 Fading

When the original dye has faded it may be difficult to define original hue and saturation.

2.2.2 Fading tones remove image

Tone dyes are the image, and when these fade the image may be destroyed too, where there is no retained silver. This is particularly true of the metallic tones, especially the various green and blue iron tones, which darken and desaturate. Any negative made from a faded tone will show a loss of detail and may become almost "posterized", giving the effect of a reduction in tonal range to just a few flat tones. The resulting negative will carry only the detail left in the print.

2.2.3 Decay

Some tone effects "decay" in a manner that creates a locally reversed [sometimes erroneously called solarized] image, in which the high densities lose more density than low densities. Commonly associated with this is iridescence on the image surface, which seems to be a redistribution of the remaining metallic silver.

It has been considered that these reversal effects could have been intentional. In our experiments we found that some formulae several formulae for producing green metallic tones were prone to this effect, but that it was almost impossible to control. We are of the opinion that the effect was never intended, may have been retained from sense of serendipity, and some may well date from the original print production, although we cannot be sure.

We do not know a method of preparing a conventional image from a partially reversed print such as this other than by digital restoration.

2.2.4 "Lacking"

Many tint dyes, especially those that seem to have been used at high concentrations, appear to have "precipitated" or "lacked" in the print emulsion to create a cloudy overall effect, that does not affect the making of a good negative but that reduces the overall brightness and contrast of the original print. Any reproduction on a clear base print film will restore this transparency, presumably to that approaching the original image.

2.2.5 Using modern subtractive primaries

It was realised that because some of the techniques were difficult [or just messy!] many previous experimenters had departed from the original formulae and had substituted modern alternatives. One technique tried in the UK and in the USA [private correspondence] had been to use the Technicolor imbibition dyes, cyan, magenta and yellow, and mix them to match the colour of tinted film. Subtractive mixing of dyes cannot achieve the saturation of some single bright dyes

2.2.6 Positive cutting

However most experimenters had rejected the entire concept because it was felt that positive cutting resulted in an increased risk of break in projection.

2.3 LITERATURE SEARCH

We concentrated on the following sources of data

* The early Transactions of the Society of Motion Picture Engineers in the USA,

* The publications of the main film manufacturers, Eastman Kodak, and Pathe, a sight of the demonstration sheets of Gevaert and Agfa, and

* A few 1920's books on film laboratory practice, [a list of the main literature used is below.]

* Catalogues and databases produced by modern manufacturers or factors of dye chemicals

* Catalogues from dye suppliers of the period

* Literature, registers and the Colour Index of the Society of Dyers and Colourists

* Industrial chemistry and engineering journals of the period

At first sight the film manufacturer’s books and data sheets seemed to be the best source, but these contained very little practical information. We found that literature earlier than 1920 was rare and there is little about the dyes used prior to this period. The practical data is often contradictory or just anecdotal, and it was clear that the laboratories must have developed their own local approaches and acquired techniques that may never have been written down.

2.4 GENERAL PRINCIPLES OF RESTORATION AT SOHO IMAGES

Our investigation in Soho Images took the original recipes, used original dyes, used modern print stocks, and was largely carried out with great enthusiasm by Soho Images chemist Bob Mabberley.

The principles we apply are

* To identify the process and if possible the original dye or dyes used

* To use modern film but the original process and if possible the original dye to prepare the restoration.

Initially we used our own judgement but increasingly Status A densitometry and tri-linear plots show us whether our trials are successful in producing visual matches and may demonstrate that we have sometimes selected the original dye.

Since we do not know enough about fading we cannot be certain of any specific effect.

Some dyes, Iron Blue, Amaranth, Rhodamine B for example are unmistakable. Others, especially the plethora of yellows, ambers and oranges, are a minefield. Surprisingly however many of the original dyes are available today, some under synonyms. All our testing and production is on Eastman Black and White Release Print Film 5302. To a large extent this was Hobson’s Choice.

Acetate and Estar based film seem to behave identically.

2.5 SYNONYMS AND MODERN DYES

A primary source of data is the Colour Index, a register of worldwide dyes and dye manufacturers, produced by the Society of Dyers and Colourists of Bradford, UK. The first Index was 1926 and all the dyes described in the literature listed in our references are shown with the registering company, the manufacturer. However such information is not always useful, since many dyes exist in different forms, fabricated in different ways to slightly differing "recipes". Since synthetic dyes are rarely purer than 80%, the rest being the originating chemicals, or their impurities, the colours vary. Croceine or Direct Blue are single unique chemical structures but exists in numerous formulations of purity and addition dye content. Furthermore, nothing prevents a manufacturer registering a name of his own, and this process of renaming has been going on for 100 years or more.

Of course these problems have beset the dyeing industry for generations, and dye manufacturers and factors have generated databases to find synonyms. Dye chemists do not like using the term synonym because the different names do correspond to slightly different products that include of the same basic dye chemical.

Nevertheless, the best method of locating a dye is to ask a manufacturer to look for the closest dye to the one you need. One dye we have use is Direct Blue and this exists in a database under 84 different "synonyms" including Chicago Sky Blue and Soluble Blue in one such database.

2.6 STARTING POINTS FOR RESTORATION

* Tinted and toned original prints

* Existing duplicate negatives made from tinted and toned original prints

* Existing duplicate negatives made from black and white original prints

* Black and white prints already in existence

We have not carried out any tinting and toning of existing prints as in 4.4 above. In this case a copy negative and print must be made or about two to four frames must be lost at each colour change. It may be possible in the future to cut out sections and rejoin them without loss if the print is on Estar.

2.7 DUPLICATE NEGATIVE AND PRINT PRODUCTION

If an existing print on Estar [see below] is not available there is a choice as which route a laboratory should take to reach the positive cutting procedure.

2.7.1 A duplicate negative made from an original is made over length at the colour changes by "pulling back" the nitrate original print in the printer to achieve a few frames extra. The advantage of this method is that the duplicate negative produced is in one length and can be printed on a production rotary contact printer in one pass. The disadvantage is the risk of damage to the original during the "pulling back".

2.7.2 A duplicate negative is made in one pass and then printed with "pull backs" during the print production process. This makes the initial duplicate negative printing easier, especially if it is wet gate. It slows down the final printing.

2.7.3 A duplicate made in one pass can be used to make two prints. This enables each colour section to be cut from alternating prints to achieve the overrun. This method is probably good for fast cut colour changes, and for occasions when time is short [and the client will pay for the extra print].

2.8 PROCESSING

Tests were first carried out in dishes or beakers with short film lengths, moving on to a crude aerial film processor for 30m [the Doran Processor], a 1.7m 35 mm spiral reel, culminating in production in a 30m spiral reel originally used for aerial reconnaissance film.

By the time we began to make reel length restorations we had made hundreds of test examples using a wide range of dyes and techniques and already discovered that there was considerably more to both tinting and toning than just following a 1925 recipe. Detailed records kept with the examples form a reference collection to refer back to select, identify or research into the images produced.

Tinting is relatively straightforward, the depth of tone only dependant on solution concentrations, acid concentration, tint time, washing time, temperatures and agitation! Toning is a little more problematic.

2.9 SPECIFIC TECHNIQUES

Some of the most important techniques that we experimented with were:

2.9.1 Copper Red Toning.

We realised during the very first tests using the Eastman formulae that the copper toning process did considerable damage to the film emulsion layer resulting in a blistered surface probably caused by excessive softening. Special hardening solutions using Tannin were in some literature. Some literature replaces copper toning by a form of Uranium toning, which produced a similar image colour, and eventually by mordant dye toning. We believe that early nitrate films suffered the same problems our Kodak 5302 and that this was why other toning methods replaced it. We decided not to continue with a copper tone as a routine, but later when we tried the Agfa formulae the results were better and the emulsion less damaged.

2.9.2 Uranium Red-Brown Toning

Uranyl nitrate like all Uranium salts is now very difficult to obtain. It is costly at £10 per gram, available from a few specialised sources, and subject to quite onerous Health and Safety legislation even though as an "unsealed radioactive source" it's radioactivity is insignificant. It is also extremely toxic. In the 1920's uranium was not only a common toner but was also the basis of a very common mordant used as the starting point for a wide range of dye toned colours. One early paper [Reid, 1917] suggests that mordant dye toning could and should replace both copper and uranium because of toxicity and emulsion damage. We decided not to use Uranyl nitrate either, as all the mordant dye procedures could be carried out using potassium ferricyanide, which yielded silver ferricyanide as the mordant image.

2.9.3 "Sulphide" or Sepia toning

Sepia was a common toner for paper prints until the 1950's and the image on paper varies from pale to dark red-brown. It was produced by bleaching the silver image to an insoluble halide salt and "redeveloping" in sodium sulphide solution to silver sulphide, which is red-brown but dense and opaque. When the process is carried out on a normal motion picture print the visual result is a "cold" greenish black. If a very thin print was used a "warm" tone not unlike copper toning was produced. We found that this was extremely difficult to repeat and a low-density print did not become as brown as the literature suggested. This may be due to differences in the modern print stock.

Sodium sulphide is an unpleasant and potentially dangerous chemical to use and needs good extraction and atmosphere testing. Mordant dye toning procedures seem to be the best alternatives today, and some original "recipes" use a mixture of Iron-tone blue and Uranium ferrocyanide to produce a sepia, suggesting that the problems we experienced were present then.

2.9.4 The toning process

The earliest photographic toning processes used many process stages: wetting, bleaching, rinse, toner, wash, sometimes clearing bath and then a final wash. We chose to try first the shortest later processes. Even these can be quite lengthy - the so-called "one-step iron-tone blue process" of Eastman [1928] was still wetting, bleach-tone, rinse, fix, wash.

Mordant dye toning was almost always two solutions - a mordant-bleach, rinse and dye bath.

2.10 FINAL ASSEMBLY

After colouring the positive print is cut together using a tape or cement splice, or in the case of Estar based film, a welded butt join is possible which just fits in the inter-frame line at each colour change. Every print has to be produced in this way. The procedure has all the disadvantages that any film of that period had - it has numerous joins and the risk of a break, if the film is not on Estar base, is higher.

So-called "eight perf" tape covers two frame completely, one on each side of the join and we have found that even the most experienced viewers are unaware of the tape.

The process is more labour intensive than almost any other laboratory technique.

2.11 USING DUPLICATE NEGATIVES FOR OTHER RESTORATION

If a repeat restoration is never to be needed the over-run and pullback frames can be removed to yield a normal duplicate negative [to print a black and white or a Desmetcolor print].

Alternatively a normal black and white or Desmetcolor print can be made from the duplicate negative by direct printing, and the extra frames cut out of the resulting print.

If the print is on Estar base and welded butt joins used there will be no increased risk of film breaks.

2.12 FUTURE PLANS

Every process can be improved and we look forward to the following research and development

2.12.1. Increasing the dye range

Continuing searches for more references, dyes and formulae have lead to a considerable increase in the range of dyes available to us. The discovery of an English version of two editions the Agfa manual in the hands of a private English collector gave us new formulae especially for metallic tones, and the Agfa copper tone is a very successful procedure. On the other hand some of the Agfa blue and green metallic tones have not been successful at all.

2.12.2 "Sepias" and warm browns

The search for more workable "warm brown" or sepia tone images still continues, although these are common in the literature, they are not common in the films themselves, and we have not researched this group of effects as much as we would like.

This area is confused by the range of colour of the developed silver image alone during the early years of this century, and by the colour of film base. The developing agents used today for black and white processing are usually a mixture of Hydroquinone and Metol [variously also called Elon and Genol] or less commonly Hydroquinone and Phenidone. Both, in conjunction with the modern silver bromide emulsions, produce a good neutral grey image.

Old silver print images vary but most are "browner" than the images of today and while some of this may be due to time or some retained oxidised developer products, probably most is due to the different formulations of developer. Many more developing agents were in use but the earliest manufacturer’s formulae for print film usually consisted of Hydroquinone alone, and our tests on modern film stocks show that these formulae produce "warm brown-black" images similar to many old prints.

[The warmer projection arc light would have added to the overall warm appearance]

2.12.3 Pastel tints

We have also identified a wide range of apparent base colours or emulsion tints that are almost subliminal on a light box and virtually unseen on projection. These too may add to the overall "warmer" image colour. We were introduced to this by Noel Desmet of the Royale Cinématèque de Belgique. There is no doubt of their existence, and the colours range from yellow to pink and sometimes green.

A few explanations for these faint tints are:

* That the original tint dyes have faded so much that the effect on projection has been lost

* That they represent the last film processed in a progressively weak batch process and are therefore laboratory errors

* That the base nitrate material has discoloured in time - this seems to be accepted by some technicians

* That the effect was intentionally almost subliminal - it is known that general colour fatigue can accentuate a colour change effect at a scene change.

None of the original papers of the period mention these pale tints.

2.12.4 Process control

We have established a process monitoring system. No such system ever existed in the past, as far as we know, but as modern laboratory technicians we felt vulnerable without knowing how variable our results are. We now use a standard LAD print on black and white film stock, measure the density of the LAD step to Status A and plot the values as a tri-linear display. Also without measurement we were unable to extend our investigation to the following.

2.12.5 Identifying faded dyes

Our moves to develop a technique to identify of the original dye and process have been moderately successful, to the extent that we can measure the original archive film and try to match it to a tested recipe or dye. With tints this works reasonably well to the extent that we can state if a dye matches the original. The major problem exists with metallic tones which are the most unstable of dyes, and for this a table is needed defining the fading characteristics.

So far all we can say with confidence is

Prussian Blue tones [Iron Blue tones] probably Darker and desaturate with including all "grass-green" tones that originate time - may become less from ferric ferrocyanides green/more blue

Prussian Blues Discolour in UV projector light

Uranium ferrocyanides Darker- may become redder/less yellow.

Copper ferrocyanides Discolour with time

Vanadium ferrocyanides No data - difficult to recognise

Non-destructive testing is insufficient to identify many of these tones, although it does become possible to recognise certain effects. Simple destructive testing is mostly impractical or inconclusive although quite easy because of the relatively large amounts of film needed to be certain [about 2-5 frames of 35 mm for conventional inorganic "Group analysis"] and because some mordant tone processes in which the main dye was an organic "basic" dye, used uranium or copper ferrocyanides as the mordant!

2.12.6 Fade testing

We would like to have investigated the effects of fading by time, temperature or projection lamps on the dyes and metal salts directly, but this has not been possible. Very little literature is available on the fading of the dyes we are interested in - there is a lot of literature on the fading of modern printing ink or felt tip pen dyes.

The logical investigation that is still available to us is to reproduce the original recipes that are found in the sample books and compare them with the old samples.

This was how the simple table was devised for metallic tones above, but there is a great deal more information waiting to be discovered from this procedure. Using modern film may alter the colour produced but not much since old uncoloured nitrate film seems to produce the same effect as modern film, at least for Orange G, Iron Blue tone and Croceine. We did find that Agfa film processed at Haghefilm in the Nederlands produced a lower density of colour than Kodak film processed at Soho Images but increasing the dye concentration resolved that.

2.12.7 Better aims for Desmetcolor

A major result of this investigation is that we are also more confident with the Desmetcolor system since we now have a much better concept of the colour of the original dye. Already the dazzling vision of recently prepared Iron Blue has stimulated tests by Noel Desmet of the Cinématèque Royale in Brusselles to show that the colour can be reproduced on modern colour film. The Desmetcolor process will always be less costly than restoration by the original tinting and toning, and will clearly be used for much routine work.

However we are now almost certain that some of the red dyes [e.g. Croceine and Amaranth and maybe Greens such as Malachite] are outside the saturation achievable by mixing cyan, magenta and yellow in a subtractive colour print film.

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