Ive hunted high and low for a solution. I can put inclined labels on bar charts:
BarChart[{{1, 2, 3}, {4, 5, 6}},
ChartLabels -> {Placed[{"c1", "c2"}, Axis, Rotate[#, Pi/4] &]}]
, but this fails for stacks:
BarChart[{{1, 2, 3}, {4,5,6}},
ChartLabels -> {Placed[{"a", "b"}, Axis,
Rotate[#, Pi/4] &]}, ChartLayout -> "Stacked"]
Where am I going wrong?