Dry martinis may have only a few drops of vermouth, while a regular martini has the full 1/2-ounce measure noted here. Be sure to ask your guests how dry they like their martinis before adding the vermouth. During the 1930s, people enjoyed their gin martinis with one-third vermouth!
The following recipe has been adapted from The Culinary Institute of America's Entertaining (2012, Houghton Mifflin Harcourt) cookbook.
Dirty Martini: Add ½ ounce olive brine and garnish with an olive.
Gibson: Garnish with cocktail onions and a little brine from the onions.
Note: Martinis can be made in large batches and mixed in a cocktail pitcher.