John Gill Commentary Mark 9:3

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

And his raiment became shining
With the rays of glory and brightness which darted from his body through his clothes, and made them as bright as the light of the sun at noon day: and exceeding white as snow ;
than which nothing is whiter;

so as no fuller on earth can whiten them .
The Syriac version renders it, "as men cannot whiten on earth"; and the Persic thus, "so as men could not behold him". Just as the Israelites could not steadfastly behold the face of Moses, because of the glory of his countenance, when he came down from the mount; (See Gill on Matthew 17:2).