wax lyrical about
wax lyrical about (or over)talk in an effusive or enthusiastic way about something.
Wax (from Old English weaxan ) was used to mean ‘increase in size’ right through until early modern English, but since then it has been superseded in all general contexts by grow . It now survives only in certain expressions, especially with reference to the moon's monthly increase and decrease (waxing and waning ).
1998 New Scientist Even as they wax lyrical about the perils of a changing climate, Clinton and Gore are presiding over the most massive expansion of oil exploration and drilling since…the Trans-Alaska Pipeline twenty years ago.