Gel

Gels are sheets of heat resistant, translucent plastic, which are coloured so that they change the colour of a beam of light. They are placed in gel holders, which go directly in front of a light. There are two main manufacturers of gels used in UK theatre, Lee Filters and Rosco International. Whilst they both produce more or less the same coloured sheets, the sheets have different colours and names. See below for converters between the two types.

Frost
Frosts are similar to gels, in that they are sheets that alter the beam from the front of the light, except that instead of changing the beam colour, they change the beam focus. Adding a frost will soften the focus of the beam, with different types of frost softening by a varying amount. Like gels, frosts will also reduce the brightness of the beam.

Gel Fading
After extended use, a gel may fade or melt in colour (especially if it has a high saturation). At this point the gel should be replaced. However, less used gels can often be used in several different productions before they need replacing.

Composite Gels
Instead of using just a single sheet of gel, you can layer multiple sheets together to create a new colour. This will block more light so the brightness of the beam will be reduced.

Gel Scrollers
Instead of using a single gel, gel scrollers can be used to change gels during a performance.

Swatch Books
Swatch books are books with a sample of every gel from that manufacturer