Dic: wax (one of its meanings as a verb)

• He waxed lyrical about the skills and commitment of his employees.
• My mother waxed eloquent on the theme of wifely duty.
• I recall Roz waxing lyrical about the flatness of his stomach.

VERB | 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.

CF:

• wax lyrical: to talk about something with a lot of interest and excitement.
• wax angry and wax wroth: Fig. to speak in anger and with indignity. Seeing the damage done by the careless children caused the preacher to wax wroth at their parents.
• wax eloquent: Fig. to speak with eloquence.
• wax poetic: Fig. to speak poetically.

.... Cobuild, http://idioms.thefreedictionary.com/wax