Rosco Supergel Information

Filters were originally made from gelatine (hence "gels") but by the1950's Strand developed acetate filters.

Nowadays there are two raw materials used in making colour filters, polycarbonate and polyester. Polycarbonate is the material able to endure the highest heat and is liable to give the longest possible life.

There are two fundamental ways of manufacturing filter. The cheapest way is to buy in clear polyester film and to dye it on one or both surfaces. You can tell a film made this way because the colour can be removed by wiping the surface with a solvent or by scratching it. In most cases it will be a perfectly serviceable filter but a problem will arise if you use it in colour scrollers. This is because during the manufacturing process the film is extruded thick and then stretched and rolled to produce the final thickness. The process puts a linear orientation into the film which causes it to shrink in width when heated. It will be prone to failure in colour scrollers.

The best filters are produced from pellets of the raw material which are deep dyed then extruded to the correct thickness and finally coated with a clear film on each side. Supergel is the only filter made this way.

Lee Filter numbers were developed by Fred Bentham of Strand. The numbering system was widely adopted in Europe. Rosco E-Colours were developed using surface coated polyester to match these European numbers.