It most certainly isn't solarised. The light source is simply a little above the lens and closer than the front of the lens. I have spent a lot of time in studios in my life, so it is easy to see. I find it rather interesting as a lighting technique. I have used it myself.
The shimmer could be from a platinum print or the silver papers from the time. Off the top of my head, I can't remember when he switched from platinum to bromide (matte then to glossy). I remember that he was still using platinum paper when he was in Mexico. Old materials were silver rich as well. A lot of his prints, as well as others from the period, had a great deal of depth to them that is nearly impossible to replicate today. Any chance you get to see his prints don't pass it up. I saw a show at LACMA years ago and I spent a few hours just walking around the gallery looking at his work. It is easy to see in person why he is a master.
If you are a member of MOPA they will probably show you other Weston's if you ask. I have seen quite a few famous images up close without glass and from my experience, if you get the chance, it will change the way you look at photographs, let me tell you....