Patinas are acids. You should wear gloves while doing this work.
After cleaning the solder beads, wash the panel off with warm water and a little dish washing liquid to remove oils and other residues. When washing use a very soft scrubbing brush to get in all the little crannies.
Dry the piece with a soft old towel. If the piece is framed in zinc, make sure that any trapped water is eliminated and the piece is entirely dry. Often letting it stand overnight will be sufficient. A panel with no moisture will help the polish of the solder lines to be more even.
Pour a small amount of the patina into a small container so as not to contaminate the rest of your patina. Do not pour the remainder back into the bottle, as it will begin to neutralise the main supply.
Apply your patina with a small flux brush reserved for the purpose, or a piece of a rag. If you use a rag, renew it frequently. Do not be afraid of putting too much on. If you are not happy with the colour when dry, you can rub the solder over with a 400 gauge (also known as 000) wire wool to abrade the surface. Then give it a further coat. Rub with a soft cloth to a shine.
To preserve the desired finish, a coat of beeswax helps, but you must remember that copper will oxidise over time no matter what you do. It is this that gives it a rich deep antique lustre.