Types of Gel

Surface-Coated Polyester

Deep-Dyed Polyester

Body-Colored Polycarbonate

Surface Deep Dyed Body Color

Lee Filters and Rosco E-Colour

GAM and many Roscolux filters

Most Roscolux filters and all Rosco Supergel filters

The easiest way to produce a color filter is to simply coat the color on top of a plastic film base.

Surface-coated polyester filters begin as a roll of clear film that is "painted" with a dye solution on one or both sides. Polyester film is widely used as a base material for coloring since it is relatively inexpensive and will accept coatings of solvent-based coloring agents.

Since no heat is involved in the process, dyes used need not be heat-resistant.

Of all three methods used for manufacturing color filters, surface coated is the simplest to adapt, but it results in filters most susceptible to fading from heat.

Deep-dyed color filters begin with a roll of clear polyester.

The film is passed through a bath of heated solvent suffused with dye. The solvent causes the film to swell expanding the polymer structure and allowing the dye molecules to penetrate the surface.

The film is then washed, and the polymer contracts to its normal form, trapping the dye molecules below the surface of the filter.

Compared to surface coating, more extreme temperatures are required to cause the dye particles to sublimate through the surface. Deep-dyed filters are, therefore, more resistant to fading than surface-coated filters.

Trapping the dyes below the surface of the plastic benefits the scrollers. In other filters where the colorants sit on the surface of the gel, the coating may begin to soften under heat and become sticky. If a scroller winds up a frame of gel in this condition, it can "glue" itself in place, freezing the mechanism or tearing the gelstring.

Because the dye is now trapped within the material and the surface is free of dyes, there are no materials that can become sticky when warm, something that can be seen with surface-coated color. This could result in a scroll that may bind and gel that will stick. This is particularly important when scrolling a warm gel back onto a string.

In a body-colored color filter, the color is inherent within the plastic substrate.

The process starts with powdered resin and dye fed into an extruder. Under intense pressure and heat approaching 600 degrees Fahrenheit, the drive screw combines the melted resin and dye into a thick "honey." This mixture is extruded through a die that forms it into a colored core of a film. Additional extruders seal this core between two more layers of polycarbonate.

This locked-in color, combined with the heat-resistant polycarbonate, makes for an extremely durable filter. The most significant benefit of using a body colored filter like Supergel in a scroller is that the extruded film has no orientation and will not shrink and buckle under the heat of a spotlight.

Other filters are made from commercial polyester film which is tightly stretched during its manufacturing process. When these oriented filters soften under heat, they "relax" causing the plastic to wrinkle in a radial pattern around the center of the color frame. In a scroller, this wrinkling can create problems such as excess noise as the scroller winds up around the spindle.

In addition, body-colored filter is extruded to the exact thickness, unlike polyester filters that begin as thick film and are then stretched and pulled to achieve the desired thickness. This "orientation" of film causes the filter to buckle or shrink – a particularly difficult situation in a gelstring. Because polycarbonate filters are extruded to the required thickness and not stretched or pulled, they will not buckle, shrink, or pull in a scroller.