COLOUR SEPARATION OVERLAY (CHROMA KEY) (1970)
Blue Peter presenter John Noakes demonstrates some of the mind-boggling visual effects that have been made possible using the Colour-Separation Overlay (CSO) technique.
Only the BBC calls it Colour Separation Overlay, by the way - feel free to call it chroma key or blue screen like the rest of the world.
Duration: 4 minutes
Suggested credit: Blue Peter (1970) © BBC Archive