Decorative cast iron was meant to be functional as well as beautiful and was used to create gates, garden statues, fences, door knobs and knockers, as well as toys. The high carbon content of antique cast iron makes it more brittle and less workable than later types of iron, and like many metals, its worst enemy is time and rust. Contrary to most types of antiques, cleaning and repainting them does not decrease their value, but rather protects and enhances them.
Brush dirt, rust and loose paint from the antique cast iron with a stiff wire brush.
Coat the object with a light spray of lubricating oil. Rub the object with a piece of fine-grit emery cloth to remove remaining rust. The oil will prevent undue scratching of the surface while the cloth gets rid of the rust.
Wipe the antique cast iron with a soft cloth dipped in white spirit to remove oil and remaining rust particles. Wrap the piece in newspaper and place it in a warm, dry place for several days to remove all moisture that will cause rust to reappear.
Wipe gently with a rag, sprayed lightly with lubricating oil, or apply paste wax with a cloth and buff. Either treatment will keep moisture away from the cast iron surface and prevent rusting.
Scrub the piece with a wire brush to remove dirt, rust and loose paint.
Pressure wash the piece of antique cast iron with a pressure washer if complete removal of paint is desired. Allow the object to dry completely.
Prime the piece with a primer that contains zinc, and allow it to dry for 24 hours before painting with rustproof paint or lacquer in the original colour. Typically, antique cast iron was painted dark green, white or black.
For small, cast iron antique toys with complex painted surfaces, you may wish to consult a conservator for professional advice on cleaning and conditioning.
Don't use a sandblaster or chemical strippers to remove rust from antique cast iron, especially if the piece is valuable.