Hello there Cary,
Leave it in the open air to get rained on or you could try using salt water and leave to dry. You could ofcourse cheat! Use an acrylic paint?
Hi! Checkout Modern Masters Patina finishes!
Here is a link
I created this effect on Pennies and this post might help you - https://chascrazycreations.com/how-to-patina-on-pennies/
Incubate with Hot Crushed Boiled Eggs
The hot boiled egg method is perfect for creating a brownish patina on copper. Eggs are hard boiled and then crushed to pieces in a re-sealable plastic bag or container while they are still hot. The copper is then placed into the bag and sealed for minutes to hours, depending on the desired shade of brown patina. The longer the incubation time, the darker the brown color. This method is ideal for small copper items, but large ones are difficult to manage through this technique.Use Miracle-Gro
Miracle-Gro plant fertilizer is an excellent oxidizer of copper. For a blue patina, mix one part Miracle-Gro with three parts water for a solution that you can spray or wipe onto the copper. For a green patina, mix one part Miracle-Gro with three parts red wine vinegar. A patina will form within 30 minutes and become permanent within 24 hours.Soaking in White Vinegar and Salt, Sawdust or Potato Chips
Soaking copper in white vinegar and salt will create a blue or green patina. Other ways of doing this are to bury the copper in sawdust or crushed potato chips soaked in white vinegar. The longer the copper is buried, the darker the patina becomes.
Spray the copper with a solution of salt water and then place the copper in a container that contains non-detergent ammonia. The copper should not be touching the ammonia liquid, but should be raised above it.
The sealed container will trap ammonia vapors that will then make contact with the copper. Be careful when handling ammonia: wear protective gloves, wear safety goggles and be near water in case you need to rinse ammonia off of yourself. Also, do not sniff ammonia and use ammonia outdoors or make sure the room is well-ventilated.How to Naturally Influence the Color of Patina
There are ways to allow the patina to form naturally without applying chemicals to it. Exposing the copper to outdoor conditions will help patina to form. Outdoor conditions include fog, rain, snow, and heat. Leaving the windows open will change the temperature and moisture content of the room, so any copper objects in that room will also experience the changes.
You can purposely leave copper furnishings next to sources of heat and moisture, such as in the kitchen next to the stove or the back of the refrigerator. Leaving copper next to a window so that it receives lots of sunlight will expose the copper to natural heat.Sealing the Patina to Keep Your Desired Color
The patina that forms from artificial methods can be easily brushed off, so it must be sealed to be kept permanent. Sealants can be wax, lacquer or a proprietary mixture of chemicals. Jewelry-making and craft stores carry multiple brands of sealants for protecting patina.
Since patina forms through chemical reactions between copper and molecules in the air, preventing the air from reaching the copper will stop any more patina from forming. Applying a sealant can also be a way to keep the patina that you like, preventing it from changing further.
You can spray it with salt water to speed up the aging process.