a company that supplied fish tanks to London Zoo, they were re-built with thicker glass after one of them burst from the water pressure. The move away from black and white sometimes caused problems as build-ups of algae in the aquaria caused the water to change colour. The illusion of scenes being set underwater was further enhanced by populating the aquaria with tropical fish of various sizes to create forced perspective.Rogers et al., p. 83. Food was dropped at various points around the tanks to keep the animals in shot. A disc with various portions cut out was placed in front of an overhead lamp and rotated to give the impression of light being refracted through the ocean, while the water in the aquaria was disturbed to create "rippling" effects. Wires were painted over to make them non-reflective and fans were used to simulate currents passing over puppets' hair and clothing. For the climax of the Stingray launch sequence, in which the vessel shoots out of an underwater tunnel, part of the set was painted onto the aquarium to conceal the air line that produced the accompanying rush of bubbles.Meddings, p. 33. Ocean surface shots in Supercar and Fireball XL5 had been filmed in an outdoor tank, but for Stingray several tanks were built inside the studio. Among the challenges presented by these shots was the need to make the scale models appear realistic while filming on water, which cannot be miniaturised. In a 1980 interview, Derek Meddings, the series' special effects director, described the process as "designing the shot carefully [...] then shoot[ing] it at very high speed (to make movement slower and therefore seemingly vaster) and hope you didn't get huge globules of water that would give the game away." Models were controlled using wires, poles and underwater tracks and rigs. To make the water look blue, the crew first tried experimenting with various lighting effects; these proved inadequate, so the water was dyed blue instead.La Rivière, p. 100. Various powders were used to create foam and whitewater. Each tank incorporated an artificial horizon system whereby the back wall was built low and the tank was deliberately overfilled to create a waterfall, blurring the divide between the rim of the tank and the painted-sky backdrop.Hearn, p. 38. The effect was sustained by collecting the escaping water in troughs and pumping it back into the tank.Rogers et al., p.