Go to your local feed store where they sell hay, etc... There should be available bags of copper sulfate crystals used to keep pond scum down. Use an old food blender (never again to be used for food) to turn these crystals into powder. In a large jar (mayonnaise is good) blend several tablespoons of this powder with a pinch of salt in warm tap water.
Before cleaning your copper-foiled work with detergent (but after a light windexing) use an old sock to sop this copper sulfate mixture over your solder lines and "magic." An aged bronze effect is instantly produced.
A bag of copper sulfate crystals will last a very very long time and is considerably cheaper than the commecial products sold in bottles.