Gather needed materials
To clean a cast-iron toy, collect soft cloths, a steel-bristle brush, a soft brush, sand paper, phosphoric acid, mineral oil, gentle dishwashing detergent and a bucket.
Scrub the toy
Scrub the toy all over with the steel-bristle brush. Scrub very hard in order to remove as much rust and dirt as possible. If the toy is very rusty, sand the surface of the toy with sandpaper. Finish by scrubbing with a softer brush to remove the debris and dust from the surface.
Spray the toy with phosphoric acid
Wearing protective clothing and working in a well-ventilated place, spray the toy with phosphoric acid. Place the toy on top of a soft cloth, and leave it overnight.
Scrub the toy again
Using the steel-bristled brush, scrub the layer of iron phosphate off the toy. Go over the toy with the soft-bristled brush to remove all debris.
Oil the toy
Rub a layer of mineral oil into the surface of the toy. Leave it overnight on top of one of the soft cloths.
Remove the oil
Use one of the soft cloths to rub off the mineral oil.
Wash the toy
Squirt a little dishwashing liquid into a bucket full of warm water. Gently wash the toy with a soft cloth dipped into the soapy water. Let the toy dry.