As Uli Kusterer was musing aloud on Twitter about how the slime in Ghostbusters II was made, I decided to pull out the ol’ Cinefex collection and look it up. This slime recipe is quoted from issue 40 of Cinefex:

For the slime corridor — and most of the live-action scenes as well — the ectoplasmic ooze was made from the same ingredients employed in the first film. Central to the formula was methocel — a thickening agent marketed by Dow Chemical — mixed with water and nontoxic food coloring. To create even more viscosity when needed, a supplemental thickener called serapan was added. “The usual formula to create thirty-two gallons of slime,” Chuck Gaspar explained, “was about eight cups of methocel to four-and-a-half cups of serapan. Then we would add about fifty cc’s of red food coloring and thirty-two gallons of water. You could actually eat the stuff. It would not have any taste, but you could eat it. The grade of methocel we used is also used in pie thickeners and salad dressings.”