Plato, Laws 769b

ζωγράφων παῖδες, οὐκ ἄν ποτε δοκεῖ παύσασθαι κοσμοῦσα, ὥστε ἐπίδοσιν μηκέτʼ ἔχειν εἰς τὸ καλλίω τε καὶ φανερώτερα γίγνεσθαι τὰ γεγραμμένα. σχεδὸν ἐννοῶ ἀκούων καὶ αὐτὸς ταῦτα ἃ λέγεις, ἐπεὶ ἐντριβής γε οὐδαμῶς γέγονα τῇ τοιαύτῃ τέχνῃ. καὶ οὐδέν γε ἐβλάβης. χρησώμεθά γε μὴν τῷ νῦν παρατυχόντι περὶ αὐτῆς ἡμῖν λόγῳ τὸ τοιόνδε, ὡς εἴ ποτέ

laying on colors or taking them off—or whatever the professional painters term the process—and reach a point where the picture admits of no further improvement in respect of beauty and lucidity. I, too, remember hearing something of the fact you mention, although I am by no means practised in that kind of art. You are none the worse for that. We may still use this fact, which it has occurred to us to mention, to illustrate the following point.