BTW, cerium oxide is a very hard material. It is used for polishing scratches out of optics not cleaning gunk off the surface.
Slightly off-topic , but I sometimes use window frosting spray as a diffusion method . I figured out that if you submerge a lens with this coating on it in some Greased Lightning for a while , the window frosting floats right off .
It's a weak sodium hydroxide ( lye ) solution . I'll bet it will remove a lot of other coatings or grime ...
I like ashes for polishing stuff ....but like anything test it first .. works like a champ on silver ware and the price is right
Here’s a tip I’ve used. If any of you are photographers you know a lens pen works amazing for removing all the difficult to remove oily haze off even the most delicate coated glass lenses. Well after doing a lot of research I found out that the black powder the lens pen uses is simply carbon. So figuring this I knew lamp black is pure carbon.
Lamp black can be bought in art stores, I bought two cans online pretty cheap and now can recharge my lens pens indefinitely so they can clean and clean and never load up with oil.
If you want to see how effective lamp black is, try this. Get a drinking glass with a smooth glass bottom, not a ceramic mug, glass. Then light a candle and run the glass bottom over the flame, you actually want to run it below the top level of the flame so it deposits maximum carbon on the glass. This is pure lamp black. Tightly fold a soft cotton cloth into a useful applicator and wipe up the lamp black. Rub that on the lens and watch it completely remove any difficult to remove oils sheens like fingerprint residue, nice thing is it removes it in a single swipe so no needless rubbing which can scratch sensitive lenses and filters. If you think you’re removing everything with just a cloth and fogging the lens. Shine a bright flashlight on the lens and it’ll reveal what you’re leaving behind still. The lamp black will remove everything.
Since this is basically how the lens pen works you can even use this on you camera lenses. I know that’s how I clean my lenses, lamp black and a folded microfiber cloth. Perfectly clean lenses.
the stuff on the A60 lenses is like a baked on film that resists all normal attempts to remove by whatotherwise would do just dandy like your lamp black technique. I’m convinced the stuff on A60 lenses is an alien technology. 
The three A60’s I got in from DX a couple of weeks ago are spotless. Also they had a properly mounted LED (no paper donut under the star).
the same time. It’s unconscionable. :cowboy_hat_face:
I’m a manufacturing engineer and am familiar with industrial glass manufacturing. If you’re talking about the hard coating that is stuck on one side of the glass, I can tell you it’s tin bloom from the residual tin used to create the original float glass. Some glass artists say steel wool and CLR will help get rid of it.
This is stellar info. Yes. Yes indeed.
I got around to finally trying this. It scratched my lens.
I used 0000 grade steel wool, new, and dry on a SF L2 lens. The lens had a couple spots of residue which I couldn't remove with windex and cotton ball which is what I normally use. The steel wool cleaned up the residue, but it left fine, swirly scratches. The scratches are very fine and hard to see, and if the lens had been very dirty, I think I would consider the fine scratches an acceptable trade-off for having a cleaner lens. But it seems like this is not a totally safe and scratch free method.
I suspect that you had either a plastic lens or a coated lens…
Solarforce L2 stock lens. Glass. Uncoated.
I’ve always used Hydrofluoric acid on all of my torch lenses, its definitely the easiest way to clean glass.
Yeap. Hydroflouric cleaned my lens totally, it’s invisible now. My lens also weighs nothing and has 100% light transfer rate afterwards. Better than coated lens!
The downside is that the lens now also let water/rain/fog/dust etc to go through. Sigh. Can’t have everything.
Bumping an old thread.
i just tried cleaning old c8 lens full with unremovable smudges and white film.
using sandpaper grit 1500 in watery condition. In few seconds already can feel the surface become so smooth.
good news: lens is clean.
bad news: visible scratches 
also try steel wool which usually to polish kitchen granite table top.
scratched even more
now need to find proper material to buff it.
And has an extreme flair for the Understatement!
Would finer grades (I have a huge bag of 0000) help/hurt/waste my time?
(Dimbo runs off to scrounge up every glass lens in the house…)
Wow! Great tip. I just tried this on a few of my lights for 10~20 seconds each & the improvement is huge!
I’m almost tempted to bring the steel wool to the glass front of my smartphone (maybe I’ll try it on my “old” phone 1st.)
Regardless, thanks for the tip. It works wonders.
DEFINITELY don’t do that. Almost all smartphone glass is coated with a fingerprint resistant coating or an antireflective coating (or both). I’d be very, very wary of that.
[quote=rollinstone157]
Thanks for the warning! I somewhat remember they’re coated but now I know for sure.