How Steel got its gleam back

The centrepiece of our celebration of steelmaking on screen, the 1945 documentary Steel features dazzling colour photography by Jack Cardiff. But restoring the lustre to a nearly 70-year-old film was no easy process, as archivist Ben Thompson explains.

Steel (1945)

The aim of the restoration of Steel was to recreate the viewing experience of the 1945 version using the earliest generation film materials, paying particular attention to the colour aesthetics of the original Technicolor Dye Transfer colour system. As this system is no longer in use it would be necessary to combine traditional film techniques and digital intermediate processes to achieve the most accurate presentation.

The Technicolor camera exposed three ‘separation’ negatives, each one recording the same frame of action but each with different light sensitivity. Thus black and white negatives were produced with different tonal values for yellow, cyan and magenta.

At the time of production these negatives made three printing matrices which held the colour dyes for recombining a single colour image onto a single piece of blank film, using an imbibition process. The complexity and accuracy required in recombining the final images makes for a huge undertaking when restoring any film shot with this system.

Steel (1945)

The BFI National Archive holds the separation negatives for the four image reels. Close inspection revealed that these nitrate base elements had survived well and contained extra footage that had been removed for a shorter version released in 1953. Following repair and cleaning, high resolution scanning of every frame of these elements was undertaken at the BFI National Archive Conservation Centre.

Also available on separate reels were the image sequence negatives used for the main titles but without the text itself. The earliest generation held by the archive that contained the text was a battered and incomplete dye transfer print made using the original imbibition process. The colour dyes had remained un-faded however the restoration team knew that the difference in image sharpness would be clearly visible if the main title sequence was copied from this print.

One frame from each of the title cards was digitally scanned. The text was lifted from the image and digitally sharpened before being shot back onto film using a laser recorder. An optical film printer was then used to reproduce the right number of frames with uneven mixes from one title card to another, thereby recreating the ‘text only’ component for re-scanning and placing over the original image background.

Having recovered every frame needed for the film, the digital image files produced were then painstakingly cleaned using restoration software to remove dirt, scratches and tears. The yellow, cyan and magenta frames were stabilised and recombined to produce the full colour image.

The three Technicolor negatives in yellow, cyan and magenta were recombined to create the full colour image
Steel (1945): comparison of restoration of Technicolor negatives; yellow

Due to low light levels in the steel works certain shots required new software algorithms to achieve accurate alignment of the three images. The original dye transfer print was used as a reference in the grading theatre to balance the colour properties of every shot as exhibited in the film’s first release.

For the soundtrack no original negs have survived but a set of duplicates were located and used in conjunction with the same original dye transfer print. After cleaning and digital transfer the two sources were edited to synchronise with every frame of the full length feature as established by the image restoration.

Audible distortions introduced by the film duplication process were removed using digital software and volume levels matched between the two sources restoring the film’s consistency as first heard and seen nearly seventy years ago.

This article appears in the sleeve notes for the BFI DVD This Working Life: Steel.

Steel is the final strand of This Working Life, a three-part BFI project comprising King Coal (September 2009) and Tales from the Shipyard (February 2011).

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