My house was built in 1940 -- the plaster is likely similar.
I've had success in nailing at an angle. Wherever possible, I use actual picture hooks, whose nail guides go in at an angle.
Forty-five degrees works well, and I'd err between 45 and 90 -- less than 45 and you will either damage the wall with the hammer or chip out a chunk of plaster.
One other trick I've heard about, but not tried, is to use rusty nails (or let untreated ones sit in salt water), as the corrosion will help them stay in the wall. This is likely more important for drywall, where there isn't much to hold things in place.
Anyway, I have a very large aluminum-and-glass frame hanging in a stairwell. It's been up for two years, and the nails are holding fine. I used to large picture brass hooks secured with 1 1/4" brass nails inserted at a 45 degree angle.