Actual 2x4’s, wooden lathe with plaster, metal lathe with plaster and then Sheetrock. Who would want to take it down to the studs when you can just add another layer 
. I guess it traps all the lead paint in between those layers, unlike on the trim work.
On the bright side I don’t lick the walls and all that lead means I can take off the tinfoil hat when I’m inside.
I swear that the “plaster” was concrete. It was far harder than today’s plaster. The lathe was also oak. I tried to use my Sawzall, but the back and forth movement would vibrate the lathe into the wall cavity and not create a hole with minimal damage around the hole. So I used one of those saws for removing grout with a diamond blade. No fun. Lots of dust too.
The house I grew up in was built in 1900 and had the same stuff. The plaster was a much grittier mix than today’s plaster or gypsum. Very grainy and gray. Even some horsehair mixed in. Then a skimcoat of fine plaster on top.
Had the same rough-sawn oak lath - maybe an inch & half wide with 1/4-3/8" spaces so the plaster would squish through creating overhangs that end up locking the plaster into the lath.
That stuff was painful to repair. 
And I’ve busted a number of drill bits trying to get into it. But once you’ve hung something on that wall it’s staying there.
Excellent job. (Though it is hard to compare with the perfection of the one bulb. 
)
Exactly. That’s the stuff.
My last place was a 1930s-40s house with forever cracking button board and plaster. I removed most of it with a small sledge hammer and a claw. I researched the material type to see if it contained asbestos, but came up empty. I replaced all the electrical in the house and added something called insulation.
At the time adding networking wasn’t high on the priorities list because kid number one was on the way and everything had to be drywalled.
We have moved since then and I have wired most rooms as needed. What a chore, itchy at times too.
Back to the chandelier, nicely detailed work!
Beautiful. Great story too. Nice work indeed.
Looks fantastic!