I use sterling silver, 14 karat gold vermeil, 18 karat gold bi-metal & vitreous enamel.
I use either a matte or oxidized finish on most of my sterling silver pieces. Oxidation creates a black finish achieved through the use of liver of sulphur.
14k Vermeil: a heavy layer of 14k gold plated over sterling silver
18k Bimetal: a solid sheet of 18k gold fused to a solid sheet of sterling silver
Vitreous Enamel: Powdered glass formulated to fuse to copper, fine silver & gold
I encourage people to clean all their jewelry, especially matte finish pieces with soap & water. This removes any oil, hair products, perfumes, lotions, etc. that build on the surface of the jewelry through normal wear.
To maintain the matte finish, you can use a very fine 0000 steel wool available at Home Depot, but don’t use the brillo pad in your sink! Also, make sure the surface of your piece is dry; steel wool rusts if it comes into contact with water. You can use a commercially available silver polishing cloth, but this will make the pieces shinier as opposed to matte finish.
DO NOT use steel wool on oxidized or vermeil surfaces. This will remove the oxidation or possibly damage the gold. Most oxidized or vermeil surfaces only need to be cleaned with soap & water. You can use a silver polishing cloth on the vermeil after any oil or dirt have been removed with the soap & water.