Ok sorry..
A bit of science with copper pans, from Herve This:
" KEEPING THE GREEN BEANS GREEN How can we put this knowledge to useand keep green beans green? First, we need to use very fresh beans whose chlorophylls have not been degraded from sitting out in the produce section of the market for too long. Next, we have to be careful not to cook them for too long, lest the magnesium in the chlorophyll molecules be eliminated. Similarly, we must avoid at all costs cooking them in acidic water, for acidity is synonymous with hydrogen, the mortal enemy of magnesium. In earlier times cooks used an ash detergent,made by filtering ashes and water, which yielded a potash solutionpotash being a base that neutralizes acids and therefore protects chlorophyll molecules against magnesium loss. Another classic method involved the use of a regreening tank, made of bare copper. Copper atoms detached from the surface of the tank replaced the magnesium in the chlorophyll molecules, imparting an almost fluorescent green to the vegetablesa dangerous technique, since copper is toxic. Fortunately, the practice of adding copper sulfate to the cooking water, which has the same effect, was outlawed in France in 1902."