Brass & Sterling Silver
Brass & Sterling Silver are metals that will darken over time. Exposure to water and heat will accelerate the formation of patina. This is a natural process and there is nothing wrong with the piece once it darkens, it can always be returned to the original color and shine.
Body chemistry, hormones, humidity and temperature, all play a part in darkening the metal. If skin discoloration occurs, hand washing with soap and warm water will remove it. I also suggest avoiding thick or oily hand creams when handling your Firstborn pieces. A thin coating of clear nail polish on the inside of the piece will also help to prevent any skin discoloration. (reapply as needed).
If the patina is too dark for your liking, first clean the piece with a dry soft cloth to remove any excess residue. Give it a quick bath using warm water, gentle dish soap and a very soft toothbrush. Be careful not to leave jewelry submerged in water. Rinse the piece thoroughly and then dry completely.
Once dry, use an all-metal polishing cloth, like the Sunshine cloth, to restore the polish and shine. Feel free to polish aggressively with the cloth, it is not going to hurt the brass or sterling silver.