Quote Originally Posted by yonsson View Post
It's not, it's tritium. Sometimes tritium gets puffy. But you can't fake tritium, just leave it uncharged and check if it still glows very faint after 24hrs in a box.
Really interesting you say that, I have a 6306 with aged dark brown like that I've always suspected is tritium, you don't often see it in vintage Seiko divers but when I have seen it it's usually in 6306s, I've brought it up a couple of times on the SCWF but no one really commented or got into the discussion as to weather it was indeed tritium and when Seiko changed to their own lume compound, it must have been around when they introduced the 6309 diver?