A.T. Robertson Commentary Mark 9:3

"and his garments became glistering, exceeding white, so as no fuller on earth can whiten them." — Mark 9:3 (ASV)

Glistering, exceeding white (στιλβοντα λευκα λιαν). Old words, all of them. Matthew 17:2 has

white as the light (λευκα ως το φως), Luke 9:29 "white and dazzling" (λευκος εξαστραπτων) like lightning.

So as no fuller on earth can whiten them (οια γναφευς επ της γης ου δυνατα ουτως λευκανα). Γναφω is an old word to card wool. Note ουτως, so, so white. Some manuscripts in Matthew add ως χιων, as snow. Probably the snow-capped summit of Hermon was visible on this very night. See on Mt 17:2 for "transfigured."