Wearing jewelry as a part of an outfit, or to complete an outfit, is relatively recent. Before the richness of, say, the past 120 years, jewelry was worn for itself in conjunction with clothing. Think of it like an engagement and wedding ring set...we do not consider whether they "go" with our outfits. Jewels and clothes were not purchased anticipating each other. They were worn without concern for "matching" or creating a "look" beyond a broad adherence to fashion (black for mourning, silhouettes for certain decades, etc).
That contributed to art nouveau's drama. Those sensual, flamboyant pieces were for every occassion. To the same occassion where Queen Mary would wear a jawdropping diamond and emerald stomacher across her bodice....
Lalique envisioned someone wearing his disturbing dragonfly stomacher- every time with the same style of clothing. It is as big as Queen Mary's stomacher, too. Bare breasts and a bug eating a dead girl- whoo! Imagine sitting across from that at a dinner party or diplomatic soiree! Guess where you would stare all night! How about worn to a high society wedding?
Diamonds indicated success and fame, even to Paris' artistic community, so Mucha's stomachers were a countercultural kick in the garters. Fashionistas have been trying to recreate art nouveau's jewels' shock and awe ever since.
In fairness, the most dramatic art nouveau jewels could only be purchased by those wealthy enough to also have more conventional jewelry, too. However, smaller pieces with the subversive design elements like menacing mythological women, dreams and hallucinations, opium references, and nudity were worn for daytime and evening daily.
