It is generally not recommended to wash a 1960s US Army steel canteen cup in the dishwasher. The dishwasher's high temperatures, harsh detergents, and vigorous water spray can potentially damage the cup's finish, cause rusting, or affect its overall appearance.
To safely clean a vintage steel canteen cup, it's best to wash it by hand using mild soap and warm water. Gently scrub the cup with a non-abrasive sponge or cloth to remove any dirt or residue. Rinse it thoroughly and allow it to air dry completely before storing it.
If you notice any signs of rust or corrosion on the cup, you can try removing it by using a mixture of baking soda and water, or by gently rubbing the affected areas with a soft cloth dipped in vinegar or lemon juice. However, be cautious when using these methods and test them on a small, inconspicuous area first to avoid any potential damage.
By taking these precautions and cleaning the canteen cup manually, you can help preserve its vintage condition and ensure its longevity.