illusion or reality

You will not be able to find information about the sort of stage magic that David Copperfield and Steven Frayne do on this website. Spells of magic is not about stage magic. You'll need to search further on the web for a site that deals with that sort of "magic".

how strong an illusion could be that the water actually freezes

Neither of the people you have asked about are using real magic. It is all sleight of hand. There is no actual magic involved. We have told you this I believe a sufficient number of times.

You have also been told that discussions of stage magicians is not appropriate for this Forum. I am locking this topic at this point.