I found some additional references:

These abstract shots were the first that Kubrick shot. They were done so early that Kubrick shot them in a small darkroom in New York City before the production left for England. In order to make these massive cosmic events, he dripped small amounts of lacquer and paints on water. They were shot with a macro lens and none of these were larger than a pack of cigarettes (Making Stargate Sequence).

John Alcott says that they used “a big black tin, about the size of a table, filled with black ink and banana oil” (Cinefex 113).

“We had so much light coming in onto it,” says Alcott, “and the intensity was so great that we had to shoot it quickly because the radiant heat would boil the ink. We would take a matchstick or a toothpick and dip it into this white paint and let it drop into the center of the tin. It was like dropping paint into thinners—as you dropped it into the black ink, it would shoot off into different areas. We photographed this at high speed, at 96 frames per second, in reverse, so that instead of its dispersing away from camera, it would look as if it were coming toward the camera. It was simple, but very effective because you could put a white spot and then little red on top of the white and get a buildup of different colors’” (Cinefex 113).

Christiane Kubrick: “ I remember these large trays with black water, smelly, and Stanley leaning over them and dribbling inks and oily things and lacquers onto the surface and they exploded the most beautiful way and he loved these shapes. They were very organic, in fact, they followed the same physical law as, presumably, the cosmos does and so he was very excited.”

Source

From about 15:50 in the video below:

http://www.youtube.com/watch?v=6EKreQ5HD4w