Engraving
Inscribed IH.W., attributed to Johannes Wierix, 1572. 

Transcription of Inscription [Lampsonius]:

FRANCISCO FLORO ANVERPIANO, PICTORI
Si pictor quantum natura, Flore, valebas,
     Tantum adiunxisses artis et ipse tibi,
Dum tibi multa libet potius, quam pingere multum
     Nec mora te limae iusta, laborque iuvat :
Cedite clamarem, pictores, omnibus oris
     Quos vel avi, nostri vel genuêre patres.

Translation of Inscription [Lampsonius]:

To Frans Floris of Antwerp, painter 
If, Floris you had acquired for yourself as much skill as you had natural ability as a painter (since you preferred to paint many things than to paint a lot,¹ and neither the just delay of the file nor hard work² pleased you) – I would cry out ‘yield painters from all lands,³ whom either our grandfathers or our fathers produced’. 

1. The Latin “multa…multum” is equally vague.   The sense seems to be that Floris preferred painting many works to expending much energy on any given one.
2. The author is referring to Horace, Ars poetica 291, where “limae labor et mora” are recommended for the poet.
3. Cf. Propertius, 2.34.65, “cedite Romani scriptores, cedite Grai” (about Virgil’s Aeneid).  The implication is that Floris could have been as preeminent among painters as Virgil was among poets.