In both "Nimbus" installations and 2012's "Cumulus," the science remained the same. The air in the space had to be kept just cool enough that water vapor (produced by, essentially, a fog machine) couldn't fully condense into rain, but warm enough that it would condense around dust particles in the air (just like naturally occurring clouds). Then too, the space had to be dry enough that the ambient moisture didn't condense the vapor, but moist enough that the vapor wouldn't diffuse out and fill the room (after all, that's what fog machines are built to do).
Artistically, the emphasis is on the lighting and the environment of the installation to create perfect photographs, but the artist must rigorously monitor these temperature and moisture conditions while the art is being made. Each successive cloud, once it falls apart, adds to the total moisture of the room, so there's also a limited amount of time available for each installation to be photographed.
What's true for the art pieces, then, is equally true for the layman: Indoor clouds are not meant to last, so your dreams of having a pet cloud are not yet reachable. However, a German design firm is working on a concept for an indoor cloud lamp which uses an Internet connection to predict and mimic weather right in your living room. Using liquid hydrogen, lamps and a high-suction vacuum system, the Nebula lamp reproduces conditions -- from warm yellow sunlight to stormy "rainclouds" -- in a way Berndnaut Smilde would probably approve. A hanging cloud, although created by slightly different means, reproduces and brings the signifiers of weather inside, making art of the everyday.