Is a grey-green surface layer on copper and copper alloys, which consists of basic carbonates and sulfates. This layer forms when in reaction with the carbon and sulfur dioxide contained in air. Patina protects copper against decomposition. In its salient green form the patina, dependent on rain quantity and water composition, appears after approximately 8 to 15 years on flat surfaces that are strongly exposed to rain.
is a mixture of basic green or blue copper acetates, which settles on copper or brass. It develops as a result to longer influence of weak acids with mostly organic compounds. Food remainders (fruit acid, acetic acid) as well as animal eliminations (urine acid) are included in the above-mentioned category.
Unfortunately these two terms are often confounded and that is why it is frequently said that poisonous verdigris might develop itself on copper garden-devices. In reality a protecting patina layer forms on the devices; this layer protects them and guarantees a long life span. It is out of the question that the food remainders mentioned in the definition above, which can be found in the compost and also be regarded as possible source of organic acids, are the ones causing the verdigris in the practical horticulture. Verdigris develops due to longer effect of acids on copper. Neither the concentration of possibly available acids by food composting nor the duration of the contact between the metal and these acids would facilitate the formation of poisonous verdigris.
The above remarks also contradict the beliefs that food, which proceeds from own horticulture by using copper soil-tilling machines, could be a danger in the nutrition of infants.