Cast iron trivets protect surfaces from hot cookware and serving ware. Long-lasting and attractive, they come in a wide variety of shapes. In most households, cast iron trivets won't require frequent cleaning. However, food or drink spills -- and sometimes corrosion -- can occur. Basic cleaning of metal trivets is not much different than cleaning other materials, but if trivets are rusting, you will need to take special measures.
Place the trivets in your kitchen sink. If you are worried the trivets will scratch the sink, place a towel down first to protect the sink's surface.
Pour a mild dish detergent over each trivet. Wet a fingernail brush (or a comparably soft-bristled scrub brush) with warm water and scrub both sides of the trivets.
Use a wet toothbrush to scrub any tighter spaces that the fingernail brush can't reach. Rinse off each trivet beneath warm, running water, then dry it as thoroughly as you can with a towel. Place it in your dish drainer until it has dried completely. Repeat this process with each trivet.
Insert a drain stopper in your kitchen sink. Fill the sink with 1 gallon of water and 1 gallon of white vinegar.
Place the rusty trivets in the sink. If the water and vinegar do not completely cover them, add more water and vinegar, using the same 50/50 solution.
Check the trivets after one hour by rubbing a cloth over them. If the rust comes off easily, drain the vinegar and water solution from the sink. If the trivets are still rust-coated, put them back into the solution and check back every hour. Do not leave the trivets in the solution overnight because the extended exposure to vinegar could damage the cast iron.
Rinse the trivets and scrub with a fingernail brush, then refill the sink with water. Add two tablespoons of washing soda to the water and let the trivets soak in this solution overnight. The washing soda neutralizes the vinegar.
Scrub the trivets with warm water and dish detergent in the morning, and follow up with a warm water rinse. Towel the trivets dry, then place them in the dish drainer.