Not a clue. That’s why I assumed it was sanded or otherwise rubbed off instead of using a chemical process. Normally, I’d expect to have to soak the thing in caustic soda then gently brush off the loose bits then soak then brush then soak then brush, then start polishing it after everything is cleaned and dried. But that wouldn’t leave the fin valleys and other concave spots intact like this.
I assumed he stuck something in the fins but looking closely at the pictures it does look like it was just sanded down.
edit: wow yea after an even closer inspection and read through of this thread…this does look like a beat up light that was sanded down just to make it look better. The lens is in horrible condition even though it was described differently. The edges are VERY rounded which would signify a sanding job vs chemical strip (and the missed ano spots). It would be hard to chemically strip an sc52 considering it is hard to take apart.
I would personally ended the deal and sent his light back but if you like it, that is all that matters. I personally run dcfix on my sc52w too so I guess the lens issue isn’t as important.
You know how they say, “beauty is in the eye of the beholder”. Well, I like my SC52 with its Zebralight coloured anodizing. Once you take away the anodizing, it just doesn’t seem like a Zebralight anymore.
Yeah. It didnot occur to me. What the f? Chemically removing the anodising left the anno in the fins? Impossible. More like sanded down…
I’m okay with how the trade went; I got about what I expected. Given that I already have an original SC52, this was interesting to me mostly because it was something different and something to keep me busy for a while. I have enough lights that this hobby has gone far beyond anything practical and is now mostly a form of entertainment.
As far as the light goes, the main thing I’ve never liked about Zebralights is the military drab color. They have at least improved this lately with darker anodizing, but there’s still an extra something about bare metal. The rounded edges give this particular light a nice-feeling texture and an unusual retro look, and in natural light it shines like jewelry. Functionality seems unaffected, so it works well as a bedroom night light and as part of an EDC rotation. I’m usually pretty gentle with my lights so the soft surface isn’t really an issue, but it would be kind of nice to have a clip.
The H52w I traded was nice, but I was planning to sell it as soon as the H52Fw I ordered (months ago) shows up. I don’t enjoy the process of selling things, so I was kind of glad to bypass all that and get something interesting out of the deal. But I do enjoy the process of taking and sharing these detailed pictures, and talking to BLF about it. 
Now I just need to stop procrastinating and start doing some mods. There’s a C8 with a de-domed XP-G2 calling my name…