The atmosphere suddenly shifted after around 20 minutes of exploring Giorgio Armani’s jaw-dropping new exhibition dedicated to his 20 years of couture. It was just after noon this Monday in Milan: Mr. Armani’s team had spent the weekend fine-tuning the installation of around 150 looks here at Armani/Silos, the four-story former granary he transformed into a museum back in 2015.

Downstairs, that team had seemed purposeful but perfectly at ease: after all, 90% of the work before this exhibition—entitled “Giorgio Armani Privé 2005-2025, Twenty Years of Haute Couture”—opens tomorrow had been completed. Placed at the center of the Silos’ cavernous atrium was a full-skirted off-the-shoulder gown from fall 2019 that had been worn just last week by Irina Shayk at the opening of the Cannes film festival. Its layered surface of white pinpoints dotted above an inky black nicely reflected the abstract starscape projected against the soaring walls around us.

Backstage at the spring 2017 Armani Privé haute couture show.

Photo: Kevin Tachman/ Courtesy of: Giorgio Armani

We moved further into the exhibition, to be faced by a triptych of looks: a long jacket, a crescent shouldered full-length gown, and another off-the-shoulder dress, this one with a dramatically angled hemline. All were cut in cream silk and sequin and positioned against a crescent moon backdrop: an evening theme was dawning upon even this slowest observer. The looks here were drawn from two seasons, fall 2008 and spring 2010: an approach that grouped looks according to affinity rather than chronology would emerge as another theme of this show.

Around a darkened corner was the first, very discreet, allusion to these looks’ lives beyond the Paris runway where Mr. Armani has shown since 2005. A small plaque alongside an eye-popping one-shouldered silver mesh gown with Swarovski floral details at the hem noted it was the very same design worn by Cate Blanchett at the 2007 Oscars. Onwards, upstairs, were sections dedicated to color, tailoring (even in couture, jackets are Mr. Armani’s best-selling garment), influences from Japan and Asia more broadly, and many others.