Stargate (device) - Making of The Props

Making of The Props

Two full Stargate props were originally built for the SG-1 pilot "Children of the Gods", the second of which was reconstructed from the prop used in the film. They are made of steel and fiberglass, and are 15 feet (4.6 m) in diameter. The second prop is less detailed, and is used for exterior scenes; in the pilot it was used solely on the planet Chulak. The primary one is fully automated and capable of rotating and emitting light. This is achieved by the use of a specially designed 15-foot (4.6 m) circular gear, which turns the inner ring on a precise pinion drive wheel, using an eight horsepower electric motor. The top seven chevrons emit laser pulses which are read by a sensor fed into a computer responsible for the gate's movement, which is consequently able to start and stop the rotation very quickly. This main prop is kept almost immovably at the permanent set of the SGC, at Bridge Studios, Vancouver.

There are further Stargate props which are no more than two-dimensional or semi-three-dimensional (jar-lid shaped) Stargates, being more lightweight and easier to erect on location. These are always filmed front-on to preserve the illusion. If a shot involves the iris, this is added in post-production, as the mechanics of it opening and closing would be very difficult to build. However, when a Stargate is filmed with just a closed iris (i.e. without it moving), a tangible prop is inserted into place.

The visual effects for Stargate SG-1 and Stargate Atlantis are predominantly produced by Rainmaker Digital Effects, a notable visual-effects studio. However, some effects, including the entire Ori battle sequence in the episode "Camelot", were done "in-house". The unstable vortex effect, both in the film and the early seasons of the series, on account of being "difficult to achieve" was generated only once and recorded from various angles; this recording was the same used for all gate opening shots early in the series. Rather than being a jet of water, it is actually the image of high-pressure air being blasted into a tank of water. The effect was achieved by mounting a jet airplane engine two feet above a water tank, and using its 180 mph (290 km/h) windstream to create the sufficient water displacement. In post production, the surrounding water was removed with computer editing, and the image of the air-jet pasted into the center of the opening stargate. This technique was only used for earlier episodes, and the effect was replicated digitally soon after to allow more flexibility in shots.

To cut down on costs, the opening of a Stargate is often just implied rather than shown, by a costless sound-effect followed by distinct lighting effects characteristic of light shining through water (as the event horizon is depicted). The DVD commentary for Stargate SG-1 explains that these effects are produced by reflecting light off large sheets of vibrating Mylar.

The Stargate itself is nearly always filmed against a blue or green backdrop, not only making it easier to paste the vortex imagery onto the scene, but also facilitating the superimposition of the "event horizon ripple effect", which is entirely computer-generated. However, if a shot only involves an open wormhole without anyone stepping through it, the crew may choose to use a "practical puddle," which is simply a back lit screen placed in the gate displaying a video of the wormhole effect. This only works, however, on a darker set, as otherwise the projection will get washed out. On occasion, the Stargate itself is also completely swapped out for a computer generated model, usually in cases where it is being moved, or is depicted in space. Series producer Robert C. Cooper explained that it often costs a lot to erect a Stargate on location, and so in some cases offworld gates are also entirely a visual effect.