So I’m walking up to Fifth Avenue from Madison on my way to see another one of those modernism shows at the Guggenheim when I find myself confronted by a gathering of women in designer jeans and LV handbags hanging out in the middle of the block. It’s not your usual museum crowd,  so I peer around and see that we’re in front of Cooper-Hewitt, the National Design Museum, which occupies the stately Carnegie mansion between Madison and Fifth on 91st Street. Looking more closely, I make out the placard in front of the building announcing what has brought out this particular demographic. The featured exhibition is titled: “Set in Style: The Jewelry of Van Cleef & Arpels.” What can I say?—given a choice between exploring modernism once again and gawking at diamonds and rubies, there is no contest. I go inside.