Russian dressing may have a base of yogurt, mayonnaise, or ketchup, although the latter two ingredients are today more associated with Thousand Island dressing. Earlier historical recipes claiming to be Russian dressing usually do have a base of mayonnaise, and are in fact indistinguishable from modern Thousand Island dressing.
Russian dressing ingredients may also include horseradish, pimentos, chives and various additional spices.
The clearness that has come to be associated with Russian dressing may be owed to the fact that early recipes for it sometimes included gelatin or aspic.
Thousand Island dressing is a salad dressing (a variant of Russian dressing), commonly made of mayonnaise, ketchup, Tabasco sauce and finely chopped vegetables, most often pickles, onions, bell peppers, and green olives; chopped hard-boiled egg is also common.