what is the pre raphaelite credo?

Boticelli is the pre-raphaelite par excellence. this is his idealized Portrait of a Lady (Portrait of Simonetta Vespucci as Nymph), ca. 1475. 

look at some influences:

Veronese Lucretia, (1580)

ante Gabriel Rosetti's Veronica Veronese, (1872)

 Jan Van Eyk's The Annunciation, (1434)

John Everett Millais' Mariana, (1851)

The group's early doctrine emphasized: 

1. to have genuine ideas to express;
2. to study Nature attentively, so as to know how to express it;
3. to sympathize with what is direct and serious and heartfelt in previous art, to the exclusion of what is conventional and self-parading and learned by rote;
4. most indispensable of all, to produce thoroughly good pictures and statues.