Fusion created some highly challenging fluid fx on, as usual these days, a pretty tight tv sched. Fortunately, we were partnered with the experienced and skilled team at Ingenuity Engine, and that paid off in a big way!
It's always challenging to create highly realistic liquids, but having them interact with real people in full camera view with 2 different liquids interacting, is a real push. But probably the hardest thing was we were creating 9 shots of continuous action, so while you are dealing with art-directing two interacting fluids, you are also having to watch for solid continuity from shot to shot. The end-stage of one sim had to work with the start-stage of the next - from fluid behavior, to fluid volume, to fluid distribution. We had to make sure the black tar was at the right level to just overflow the tub and that it was overflowing in specific locations, with specific character, consistent in each shot.
The Ingenuity Engine team created high quality match-moved digi-doubles of the women, allowing us to create high detail water in the tub interacting with them, and then to insert in a layer of tar/oil on the water. Getting nice, controlled interaction came down to creating a push-and-drag rig at the margins of the tub and to move the tar over the surface, and using a couple of python-scripted force fields at the interface of the water and tar, plus applying our smorganic tool to the tar to make sure it remained a coherent, smooth layer of fluid (with no webby holes) no matter what action happened.
For the climax of the sequence where the tar is forcefully jamming itself into the witch's mouth (creepy!), we designed a 2-level force-field that would give the tar the right feeling of sinister-crawly intelligence that the action demanded. The outer level force-field is a planar horizontal, vertically bounded funnel force that drives the fluid along asymptoting paths toward the back of the girl's mouth. As it slinks toward her mouth, that force trails off while the inner force picks up. The inner force was dubbed "the skin-crawler". As soon as fluid contacts any part of her skin, it is pushed with a force that is directed parallel to her skin and pointed toward her mouth. This "crawls" the fluid over her body like a swarm of centipedes.
Another perfect combination of RealFlow and Fusion's in-house tools (especially our bad-ass smorganic!) Oh, and don't get those witches mad at you! (see Ingenuity Engine's Salem FX Build: youtube.com/watch?v=eyTZZLec9ho