Dic: wax adj about/on..

• He waxed lyrical about the skills and commitment of his employees... 
• My mother waxed eloquent on the theme of wifely duty.
• Journalists wax lyrical about the band.

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■ [VERB] V adj, V adj △If you say that someone, for example, waxes lyrical or waxes indignant about a subject, you mean that they talk about it in an enthusiastic or indignant way.

■ wax sentimental/eloquent/lyrical etc: to talk with extreme feeling, liking or pleasure about something - used humorously

.... COBUILD, LDOCE

• The Marquis d'Argenson was the first man to wax passionate on the economic advantages of governments leaving trade alone. To govern less, he said, one must govern less('Pour gouverner mieux, il faudrait gouverner moins.') ─ J. M. Keynes, The End of Laissez-Faire (1926)