This is something that I have just recently needed to learn for a client. I thought I might share with you the process, so you can do it for yourself. If you don't want to assemble all the needed materials yourself, you can just get a patina kit here.
• X-Acto knife
• Staple remover or a pair of pliers
• Clear packing tape
• Drop cloth
• Protective goggles ($2.97 at Home Depot)
• Heavy-duty rubber gloves ($3.29 at Home Depot)
• Sprayable paint stripper ($9.26 at Home Depot)
• Paint scraper
• Patina solution ($4.99 for Modern Masters Metal Effects Blue Patina Aging Solution at Janovic)
• Kitchen sponge
• Sea sponge
• Glass or bucket (for water)
• Gold, copper or black paint (we used Modern Masters Metal Effects Rich Gold, $11.99, at Janovic)
STEP BY STEP
1. Place the mirror face-down and carefully cut through the paper backing with an X-Acto knife. Peel away the paper, exposing the mirror’s backside and as much of the framing as possible.
2. With a pair of pliers, remove any staples that may be lodged in the frame. This eliminates interference with the backside of the mirror.
3. Use clear packing tape to line all four edges on the backside of the frame; this protects it from being damaged by the paint stripper. If you’d rather create a warped, antiqued look on the frame itself, skip this step.
4. Lay the drop cloth over the area where you will be working, preferably a smooth, flat surface. Wearing protective goggles and gloves, spray a thick, even coat of paint stripper on the back of the mirror and allow the solution to sit for 15 minutes. Once the paint on the back of the mirror begins to bubble, use a paint scraper to gently remove it, revealing the mirror’s silver leafing.
5. Thoroughly clean the mirror’s exposed surface under running water or by using a damp washcloth. Make sure that the mirror is completely dry before continuing.
6. Soak a kitchen sponge with water and set it aside. Pour a moderate amount of the patina solution onto the sea sponge and dab it onto the silver leafing (depending on how heavy you want the patination to look, you can also pour, spray or wipe the solution on). The silver leafing will begin to corrode immediately; as soon as it has achieved the desired effect, pat the sponge soaked in water over the silver leafing to stop the chemical reaction, otherwise it will eat straight through the silver finish.
7. To seal the back of the mirror up and protect your handiwork, paint four layers of gold, copper or black paint over the “antiqued” silver leafing, allowing each coat to dry fully (about 20 minutes per coat). Gold paint will create a sepia tone, copper will appear rusted, and black will give it a charcoal feel.
8. Hang or lean your newly distressed mirror, with strategically placed vintage bottles and flickering candles around it. Fin!
Information found here.