In my book, ‘natural’ is the opposite of ‘artificial’. The latter is defined in the (2017) Laws as ‘A bid, double, or redouble that conveys information (not being information taken for granted by players generally) other than (or in addition to) a willingness to play in the denomination named or ...
As I play over a strong notrump, 1NT-2♣-2♦-3♦ is ‘Weissberger’: 5-5 majors, invitational or better.
1NT-2♣-2♥/♠-3♦ is a fit in the major and forcing to game at least.
A diamond suit, with or without second suit, is shown via an immediate transfer.