Pewter is an alloy that contains tin, with a little copper and antimony, according to Wisedude.com. It contains a minimum of 90 percent tin. The other ingredients in pewter improve its hardness. Pewter normally has a whitish or grayish-silver look to it. Over time, it turns darker on its own. An oxidizing process can darken it to make it look older more quickly. Pewter pieces with this darkness, or patina, look more attractive. You must take care when using chemicals on pewter because you can easily damage the soft alloy.
Handle and use the pewter piece often to darken it naturally, according to Danforthpewter.com. Handle the pewter repeatedly and the patina turns darker.
Check the care label on the pewter piece. If it's dishwasher safe, put it in your machine to create a patina. Because pewter is soft, place it away from the water sprayers, the detergent dispenser and the direct drying heat. Place it securely in a rack so it can't fall through or move around.
Finish filling up the dishwasher racks. Don't place other items on top of the pewter. Add the usual amount of detergent you use for a full load. Run the pewter through a normal cycle to darken it. The heat causes a patina to form on it. The finish of the pewter turns darker each time you run it through the dishwasher.