Singing Verdi is next in my historical singing survey after bel canto I and II. I will try not to humiliate myself.
Bellini died in 1835, and Donizetti died in 1848, leaving the field free for Giuseppe Verdi (1813 – 1901). By the time of Donizetti's death Verdi was already famous for composing Nabucco (1842). I think fully mature Verdi is assumed to begin with Rigoletto (1851), La Traviata and Il Trovatore (1853).
Verdi is always a bit more crisp, a bit more dramatic than Donizetti, a bit heavier on the bass drum, but I would like to argue that La Traviata is still basically in the bel canto style. Bel canto singers could still sing it. We would expect by this time to hear only tenors singing in the heavy style, and this would be reflected in the writing for tenor.
In our time we are accustomed to hearing the very heavy technique of late Verdi singing carried back into the earlier pieces, even occasionally into bel canto, but there is no reason to suppose that in 1850 you would have heard anything like that. Juan Diego Florez's excursion into Rigoletto would not have sounded odd to them as it undoubtedly does to us. However, he would already have been heard as old fashioned. The technical shift toward heavy singing came first with tenors.
Gilda (1851) is fully leggiero. Aida (1869) is fully legato. Between these dates was a complete revolution in singing. Leggiero technique disappeared completely and was replaced by a fully legato, heavy style. The most significant change was in the soprano voice.
Professor Gossett and I discussed the problems in singing Macbeth, an opera that was composed originally in 1847 and revised in 1865. It is an opera that spans two very different eras and embodies fully the technique of both.
Here's what he actually said. "Good. I understand what you are saying, and I do agree. The other night I heard a recording on the RAI of Franco Corelli singing "Quando le sere al placido" from Luisa Miller. I swear to you it sounded as if I was listening to [Mozart's] "Esultate!" This is not to say anything bad about Corelli as a voice and as a singer, but the style seemed to me totally wrong for Luisa Miller. Perhaps that experience prepared me also for enjoying the very very different approach that Florez took to music from that same period.
"Macbeth is a complicated example, because what we usually hear is a mixture of 1847 and 1865, so that it is hard for a singer to know WHAT kind of vocalism he or she should employ!!"
This was a response to my email "I am very interested in your views about styles of singing, in particular as it relates to your specialties. It is now extremely common for very heavy singers to take on all of Verdi and substantial parts of Donizetti and Bellini. It might be possible to assume that heavy style developed gradually. I didn't really care for La Favorite to be sung so heavy when I heard it in Vienna.
"I think by Forza and Aida it is supposed to be heavy, but maybe that's what is wrong with Macbeth. She was imagined to be lighter. This is a subject in which I am very much interested. I see no reason Florez shouldn't sing Rigoletto. I'd like to hear it some time."