In the 70s, one of the Photographers I knew, Mike Carmicle, who had a studio in Sacramento he took an Kodak 3 element 80 or 75mm and used a light, very light sand paper, maybe an Emory pad and in very light moves treated the front element. From I recall he treated the out side so it had more of a diffusion effect. Not sure how many passes he made, he told he did a bit, then tested until he the effect he wanted. I have a still life he did stashed in storage, I'll see if I can pull it and scan it.