By means of a steam generator the bubbles turn out a bit hazy inside. In order to blow hazy bubbles out of your tube, you need to take a tube of large diameter and send some steam into it. The heated air will propel the bubbles upwards. You can do a trick with a steam generator on a
glowing desk. You can fill the bubble with hot air, and when it comes off the desk, it will also fly up. It turns out very spectacular, the audience is thrilled.