HORN - A white cloud in a white chapel. Just a moment and then it disappeared. Artist Berndnaut Smilde announced on Thursday clouds in the Hoorn Lady Chapel, for a fascinated public. Bell 17 hours the first cloud floats through the chapel. Shortly before has Smilde spraying the room with plants considerably blurred. With a touch he lets some smoke escape. The water binds to the smoke. Magically, the cumulus cloud is almost perfect. Joe is excited Neefjes. 'This is sensational. I do not often get the shivers, but I do now.''
I used Google Translate to translate the video description from Dutch to English. I have no idea what they are saying in the video but you get to see a guy make a cloud in a chapel using smoke and some kind of spray.
From: Here - which is in Dutch.