I love the idea of finishing off a black-tie ensemble with a smart boutonniere as was popular with young blades back in the 1930s. However, in this age of stripped-down minimalism I fear it would come off as a bit too dandyish. I have no such compunctions about a pocket square though.
The classic rule with evening wear is that the handkerchief be of white linen, preferably hand-stitched. Silk is a more modern variation but some feel that the outfit’s satin lapels and accessories already supply an ample amount of sheen and adding any more is gilding the lily.
The arrangement is largely a matter of preference. Some men lean towards the dégagé flair of a nonchalantly stuffed handkerchief and consider precisely folded shapes to be too studied. Personally, I love the simple square shape known as the “TV fold” for the way it evokes the Rat Pack era when combined with a sleek shawl-collar jacket and relaxed turndown-collar shirt.
The only time I opt for silk is as a substitute for a scarlet carnation. In that case the irregular shape of the puff protruding from the breast pocket parallels the natural asymmetry of the bygone lapel flower. Just make that sure the rest of the outfit is strictly black and white (as you would with any other type of coloured accessory).