Last year 9 lost episodes were returned to the BBC by the archive recovery organization TIEA. This is what then happened to the films while restored by the specialized team: the film starts with the remedial work required to get the film on the film cleaner, then the film cleaner at work.
The film cleaner works by immersing the film in a bath of specially engineered inert fluid which acts as a transmission medium for the powerful ultrasonic waves which shock the dirt on the surface of the film and loosen it to allow it to be gently scrubbed off by rotating lambswool rollers submerged in the bath. Hot air knives dry the film as soon as it leaves the bath.
Then the people could see the first of the film watched for the very first time since it was lost.