Patina--vinegar (white or apple cider) and salt. For small items, fill a quart yogurt container half full of vinegar, and sprinkle in about 1 tsp salt. Add any metal you want to 'age'. Seal if you touch items a lot
Here's a fun winter garden idea for an especially chilly day. Fill up some balloons with colored water (please use a natural dye). Once frozen, remove the balloon and voilà! You now have giant colored ice marbles in your garden!