While making acrylic collages, I stumbled onto a technique. I start on glass, and make layers of Golden Acrylic Gloss Medium, a layer of texture(dried leaves, lace, glass beads), and a layer of gold composition leaf, or copper leaf. When I put a layer of the Gloss Medium over the metal leaf, during the drying process colors come up spontaneously. The colors are patina-like ranging from gold greens to deep blacks with intense turquoise. The color range is dependent upon the drying rate of the acrylic medium. Humidity, airflow and temperature come into play. The brand(alloy) of the metal also affects color. Once the layer is dried, the colors do not change again. I can pull the sheet off of the glass, and cut it up for collages. I do demonstrations of the technique locally in San Diego. When they ask how it happens, the best I can come up with is "Magic"...Is there a more scientific explanation?
It sounds as though you have an interesting technique. One of the reasons we don't make that many true metal paints, especially bronze powdered pigments and others, is because these materials react with the acrylic paints.

The most obvious reaction occurs because the acrylic paints are waterbased. As you stated, the environment and drying rate has much to do with the various effects you can develop.

Another aspect of acrylics is their relatively high alkalinity. The average pH of our products is 8.7, which is because of additives like ammonia and other pH raising additives used. This is a vital part of acrylic paint stability, both while the paint is made and for long shelf life in the store and studio.

I recommend experimenting with retarders, ammonia, and possibly our pH-reducing Additive (custom product available by calling our Customer Service Dept.) Varying the pH with salts, acids and alkaline solutions may offer you interesting results, more control and insight regarding reactions.