Glass jars. I suppose they needed the metal that would go into cans for the war effort, too. What hell to deal with WWI only to be faced with WWII soon after with a whopping huge Depression in between. Urgh.
Very true - I never thought of that before! But I have some old glass pickle jars of my granny's and they're nice thick glass - I bet they're pre-WW2 and that's when they started making them thinner.