This summary of Del Monaco activity with Decca is a veritable historical document.
It encompasses his vocal parabole from the start to the end, via crisis and resurrection. The early recordings show a voice that had (and has) no equal in terms of ring and volume. His interpreations were accurate and insightful as the first 2 reviewers appropriately noted. Listen to the almost wispering start of
"Vesti la giubba" from Pagliacci, he is the only one to do it, showing a total respect for the drama of Canio, or the dynamics of "O tu che in seno agli angeli" from Forza del Destino, or the very accurate account of " Cielo a mar" from Gioconda
this to say that he was very insightful in his approach. Certainly he was a son of his time and some things (sighs and laughters) are now looking obsolete, but the artist was a serious one. He suffered a vocal crisis around 1962-1964 period
(the recital with Mantovani and the Italian and German Arias, original LP title,with Isabeau and Francesca da Rimini etc were both frankly terrible)worsened by the road accident he was involved with, that kept him away from vocal exercise quite a while. During that period that started showing its first signs in Otello with Karajan (see my review there in case of interest)his vocality was a shadow of itself. A(for him) disastrous Carmen (1963, with Resnik, Sutherland, Schippers) bears also testimony. During this period he recorded also Adriana Lecouvreur with Tebaldi and Tabarro (again with Tebaldi)but the troubles were luckily far less noticeable. He finally resurrected in 1965 with the Sacred Music recital when his voice turned again to the voice of the past if somewhat "heavier" but never the less "recognizable". His last effort Verdi Arias was commendable for the discovery of less famous pieces of the composer but the voice (he was approaching 55) shows more of the same heaviness, still the volume and the ring are there but age was there too. During this period he recorded Cavalleria and Norma with Suliotis, Wally with Tebaldi and Fedora with Olivero and the voice is exactly as I mentioned, clearly "recognizable" but heavier less agile than in his prime. In the end a commendable issue by Decca for one of their top sellers (with his beloved Renata) before the arrival of Sutherland / Pavarotti era. Incidentally Decca had quite a run with Tebaldi/Del Monaco and Sutherland/Pavarotti, lucky people.