Black partlet examples mount up.

And over at Starlight Masquerade we find an unattributed portrait with a third black/dark partlet. I'd call that a pattern.

Now I'm most intrigued by what it may mean. Does it indicate something about the wearer? Is it a portraitists concite? A local fad? Widowhood seems an obvious possibility but there just aren't enough of them to support the idea that it was a common practice. Fascinating...