TARDIS being moved across Vortis and the establishing model shot of the TARDIS's materialisation; the one-third scale prop created for The Romans was used. Martin wanted to use a greased neutral-density filter on shots of Vortis to capture its thin atmosphere, but found that the optical glass was too expensive, opting for a cheaper alternative; two special lenses were fitted, both of which broke at some point during production. Some of the bird's-eye view shots were achieved by using mirrors. Several of the shots featuring Barbara were filmed in advance from 6–7 January to accommodate for Hill to take a holiday; she missed rehearsals of The Romans to film these. Rehearsals for the first episode began on 18 January at the London Transport Assembly Rooms in Wood Green, and weekly recording for the serial began on 22 January. The second episode's recording session, on 29 January, overran by a costly 16 minutes due to several production problems leading to seven retakes; among the problems were broken costumes, actors walking through shots, scenery problems causing actors to forget their lines, and a cast member speaking unprompted. The third episode, recorded on 5 February, was beset by similar problems, including a delay in the delivery of some sets, camera failures, and a delay with the studio lighting; the recording overran by 37 minutes. The recording had finished so late that the dressing room lights were switched off by studio management, forcing the crew to exit in darkness. Following the recording, Lambert asked Martin to avoid allowing the actors to alter their dialogue, noting that major changes should be suggested at readthroughs with Spooner present. Fifteen bags of seaweed from Cornish Manures were requested as set dressing for the fourth episode; during recording on 12 February, the seaweed emanated an overpowering vegetable smell under the hot studio lights. William Russell was absent from rehearsals for the fifth episode on 16 February to film for the subsequent serial, The Crusade. Hartnell's granddaughter Judith Carney (later Jessica Carney) visited the studio during the fifth episode's recording on 19 February. The final episode was recorded on 26 February, and the session overran by 15 minutes due partly to sound problems necessitating a major retake. For the final episode, the crew treated the set more carelessly to achieve the damaged look they were seeking, as they knew it would not be used again. Throughout filming of the