Sinappikaasua October 2008, Pepino and Talavera de la Reina Ø 7 x 9.5 cm Full jar of French mustard, permanent marker on label, fabric, rubber band i Sinappikaasua (Finnish) = Mustard gas. Mustard gas is a vesicant chemical warfare agent with the ability to form large blisters on exposed skin. It is yellow-brown in color and have an odor resembling mustard. Mustard gas was first used effectively in World War I by the German army against British soldiers Mustard is a typical condiment of the Christmas ham in Finland and a common gift during the holiday season.