The animation cel story

Brian Clark of Film Sales Ltd directs our attention to a basic material many of us take for granted.

Animators are only too familiar with cel even if, in common with learned reference books, some know it as cell. It is an interesting reflection on this raw material that whilst the animation industry has grown, the number of cel manufacturers around the world has declined from about eighteen – when Film Sales was established 21 years ago – to a present world total of four or five.

There is some difficulty in being really specific – because countries use what has been traditionally available, and quite frankly it is amazing how standards of acceptance vary! In that respect and doubtless at the risk of cries of protest, I make the charge that British Animators are among the most privileged, having two of the residual film manufacturers and arguably enjoying the highest world quality standards.

The translation of cel (or cell) into Italian ‘cellula’, French ‘cellulo’ and German ‘zelluloid-montagcmaske’ gives away its derivation from that good old 1869 English invention celluloid, then called Parkesine after its inventor, based on the original highly involved method of making the first thermoplastic sheet products.

Celluloid, chemically named cellulose nitrate, being a close relative of gun cotton, suffered from a tendency to combust, sometimes quite spontaneously, but nevertheless from 1891 the US Celluloid Company produced 300 foot lengths of 5 thou. film by drum casting, which provided a film base for cine – and subsequently cel for cartoon animation.

It is believed that Disney was still using celluloid in 1929 on The Skeleton Dance, but both properties and production of the film base left much to be desired! Celluloid was ideal for such eccentricities as inflammable envelopes for phosphorus incendiaries in World War Two, — but, apart from the fire risk, animators were not so attracted by its tendency to yellow and become brittle with age. Even its surprising strength, optical clarity and a surface able to accept a wide range of artwork media could not compensate for its obvious limitations.

A non-flam home cine alternative had been in limited production from the early l900s, but it was not until the 1930s that ‘acetate’ film for animation emerged on a commercial scale. Both celluloid and acetate are based upon chemical modification of cellulose of which cotton linters is the best quality source with wood commonly used for lower quality grades. The production was similar – ‘flake’ of cellulose nitrate or cellulose acetate being mixed with plasticizers to give flexibility and improve water resistance, and the resulting mix dissolved in an appropriate solvent such as alcohol for nitrate or acetone for acetate to produce a viscous dope.

In the early days of nitrate production the dope was cast onto a drum which was typically twelve feet in diameter and probably silver coated from which any surface imperfection would faithfully reproduce every turn of its 38 foot circumference. As the drum revolved the dope lost its solvent to atmosphere leaving a rigid film to be pulled away and reeled after nearly completing its revolution.

By the time acetate became established the casting unit had transformed itself into a sophisticated enclosed machine housing a polishable resin coated band nearly 200 feet long and 4 feet wide, with complex zoned temperature controls and several hundred drive, guide and web rollers. The efficiency was dictated by the amount of solvent that could be recovered – commonly as much as 96 per cent of the original amount.

Until now the term ‘acetate’ has been used as if there was a sole alternative to nitrate, and that its difference was only to do with the resistance to combustion. As with all changes many paths were followed encouraging considerable diversification away from the traditional photographic film monopoly if the casting process. The early acetate mentioned above was actually ‘diacetate’, which may seem a little curious as its properties are inferior to triacetate, and, to make diacetatc the process must first produce triacetate, and convert it, by hydrolysis, to the di (or secondary) version.

The reason being that whereas acetone as solvent for diacetate was well known, it only softened triacetate (as it is much more chemically resistant) and production of Tri had to wait until a suitable casting solvent, methylene chloride, was in bulk production. So it was not until the late 1930s that tniacctate finally threatened celluloid in both photographic and animation outlets. Since then it has had a virtual monopoly of 35mm film stock and, at least in the UK, dominated animation cel. Triacetate production in the UK, established as a source for Ilford, was of such a quality that once used by animators any lesser alternative would be difficult to accept.

Cast Diacctate, manufactured mainly for lamination and packaging, has always been available, but, based on wood pulp and made on non-photographic casting machines it never achieved the surface or optical qualities of triacetate. Inherently it also tends to be blue dyed to disguise its poorer base transparency, which, for the animator creates filtration problems at camera if multi-layer shooting were to be attempted. It must also be said that diacetate is less stable due to its water absorption and has a softening point in the 1200-l400c region – 500c or so below treacetate.

Strangely, extruded cellulose di-acetate, unacceptable in the UK, with its faults accentuated by its lower cost, higher output production process of local manufacturers finds application as cel in some other European countries. To high background colour is added an inferior surface finish compared to casting which restricts the number of layers possible to a probable three or four at most compared to six and eight for cast triacetate.

Despite the speed of today’s communications and the benefits of the EEC it seems from Film Sales findings at the 1987 Annecy Festival that many animators in Europe have never been exposed to British triacetate, which, though more costly per cel would doubtless show significant overall production savings and enlarge its capabilities!

Film Sales of Woolwich was established in 1966 as the UK distribution centre for British made photographic triacctatc animation cel. Since then capacity has been commissioned to cut and punch all field and panning sizes with continuous, double and triple Acme standard punching — or specials where quantities justify. Cast diacetatc was soon incorporated into the range — but its use has been noticeably limited to hobbyists, titling and simple two or three layer animation where the blue colouration of the film could be easily compensated.
Animators are always anxious to win their crock of gold with an ever better cel, and with this in mind have looked at numerous alternatives to triacetate, but to date nothing has bettered the products of the 1930s! An obvious candidate is Polyester film – already very successfully exploited by ICI. Its properties are superficially attractive – extreme chemical resistance, lustrous surface, strong accurate thickness and high heat and dimensional stability to name just a few! For photographic films outside of 35mm or 70mm roll stock it is nearly ideal – and is a major contributor to the diminution of cast acetate producers from that figure of eighteen mentioned in the first paragraph.

Incidentally, cine film stock remains exempted as polyester is just too strong – camera mechanisms can shatter before the film does; its chemical resistance makes splicing just that bit more difficult and, an odd quirk this, it tends to tangle badly in the editor’s bin. By good luck, triacetate has none of these problems, though it must be said that neither did celluloid!
The polyester carrot for animators is the high heat-resistance tag – with visions of effortless copying to replace tracing. Well, nothing is perfect and even polyester is not quite so good as triacetate at transmission and base colouration, is more fussy over what paints it will accept, and shows blocking marks on overlays. But at first glance it looks good for copying using the plain paper copier.

In 1987 the removal of tracing with copying is hot news, although those who used to do lust that with the Xerox 1385 copier in the early 1960s may not think of it quite that way. They are obviously in the minority and the benefits and technicalities of copying are of sufficient importance to be the subject of another article.

Printed in Animator Issue 21 (Winter 1987)