Hollywood -- it is not a mask that Roddy McDowall, Booth Colman and Mark Lenard wear in 20th Century-Fox TV’s “Planet of the Apes” series that airs Fridays on CBS-TV. It is an “appliance” which takes three-and-a-half hours to create each working morning.   “The only objects we can save to use another time,” says co-creator of the appliances, Dan Streipeke, “are the ears. As for the rest of it, my makeup artists start from scratch at 5 a.m.” And Streipeke is particular to call them makeup “artists” because in a sense, they are sculptors.   For the first step, a life mask is made of the actor’s face. The substance used is Jelltrate, which dentists use to make impressions for bridges and false teeth. Next, an impression is made of the face in dental stone. Then the sculptor adds in clay features of the class of apes to be portrayed -- gorilla, chimpanzee or orangutan. These are then fitted together and a special formula of foam rubber is pumped in to fill the difference.   When it is set, the rubber is removed and cooked in an oven for six hours at 200 degrees. This, then is the basic “appliance.”   The appliances are sprayed with special coloring which clings well to rubber. The edges are feathered and the apertures, such as the eyes, are cleared and a channel cut through the roof of the mouth so that the actor can breathe.   The reason for all this care and expense is that a major secret of the success of the series is the capacity of the actors to convey emotion through expression.   “One has to learn to exaggerate facial movements in order to energize the appliance,” says star Roddy McDowall. “It’s rather like that old trick of patting the stomach with one hand and circling the head with the other, but it can be done. Otherwise, all one would have is an expressionless, lifeless mask.”   The appliance cannot be removed as long as the actor is working, and he can subsist only by taking liquids through a surgical straw.   On a hot day out on location, some actors wearing appliances in costume often drop ten pounds in weight.   Roddy McDowall has quite often had to keep his appliance on for 13 hours.   During the laborious three-and-a-half hours while he is having his appliance put on, Roddy “psyches himself out” by listening to classical music on a tape recorder.