Lately I've been watching quite a few Warner Bros. shorts from the 1960s, and I've noticed in the '60s that many shorts don't end with an iris-out like they were known for, instead just fading to black at the end. Considering how many cartoons from that decade I've noticed it missing from, I think it's safe to assume that Warner simply stopped putting it in their cartoons.
But does anybody know when Warner stopped putting an iris-out at the end of its cartoons? Or what the last classic cartoon was to have an iris-out? I've recently watched a few early 1960s cartoons, Person to Bunny and What's My Lion?, and saw that those two ended with an iris-out (I also know those might have been in development for a few years before they were released).
There were occasions before where cartoons just faded to black at the end, but most of those (Hare 'Um Scare 'Um, The Heckling Hare, Hollywood Steps Out, The Stupid Cupid) had their original endings cut upon release (so the missing endings probably did have iris outs). Though I've also noticed the earlier A Tail of Two Kitties and Show Biz Bugs also just fade to black, and I don't think those had anything cut at the end (considering how A Tale of Two Kitties ends, it seems like a clever exception).