The black HTC One S uses a process called micro arc oxidation (MAO) to harden its aluminum unibody and make it feel like ceramic. We've recently experienced some chipping on the finish of one of our review units, so we reached out to HTC to find out if this is a known problem. Turns out we're not the only ones to report the issue, and while rare, the company's gone ahead and tweaked its manufacturing process and is offering to swap affected phones for free for existing customers. Here's HTC's statement:
HTC is committed to delivering a high quality product and great experience for all our customers. There have been a few, isolated reports of this issue. The finish on the One S was laboratory tested as being at a hardness similar to ceramic. While that's hard, it doesn't mean it's impossible to damage. Regardless, HTC takes quality very seriously and are providing all customers with an immediate fix and we are implementing some small changes to ensure customers do not experience this issue in the future.