It sounds natural (of course other than "unzip, "come undone") to use open with zips. Like (if they sound natural)..
Open your zipper.
Your zipper is open.
But it does not sound natural to say:(now the unnatural ones
Your button is open.( unnatural)
Open your button.(unnatural)
Why is this difference? Why is it only "undone" and "do up" for buttons but "open" sounds okay for zippers (along with alteranatives of course;>)