I finally got the opportunity to access my friend's science lab over the weekend and it was hell of a fun time. I've managed to recreate the original x-metal grey finish amongst other crazy things. The test subject was a very beat up pair of R1 in XM grey with heavy scruff marks and scratches. Here's an arm that's restored in original the glory of XM grey. The other crazy results from other beater pairs resulted in "X-Metal Polished Grey" and "X-Metal Black Chrome". All of these were achieved without painting, photoshopping nor electroplating. It's pure mad science chemistry.