(2) The bronzes found in water, as for example in the beds of lakes and rivers, are less perfectly preserved. They have usually a thin coating of a calcareous deposit, which however often allows the lustre and colour of the metal to appear in places. When such bronzes have dark or green coloured patches or spots, the layer is very thin and may be removed by treatment with acids, which allows the metallic colour to become visible. Bronzes preserved in water still retain the same definite edges and points which they possessed when they entered the water. If bronzes which are markedly incrusted with verdigris are found in water in all probability they had lain in the ground a considerable time before being covered with water, and oxidation had penetrated deeply into the metal before immersion.
(3) Bronzes found in the earth or in graves appear covered with a fine green crust of verdigris which may be either light or dark in colour and which often has a vitreous lustre. This is generally known as Patina.
This crust varies in thickness from that of writing-paper to several millimetres. If the green crust be filed away, or better, removed by dilute nitric or sulphuric acid, the bronze is found to possess a reddish colour; below the crust of cupric carbonate is found a layer of cuprous oxide, which may be removed by ammonia, thus revealing the metal with its characteristic colour and lustre. This condition is characteristic of the slow oxidation of bronze in moist earth. The layer of cuprous oxide between the pure metal and the external crust of copper carbonate has been shown by the examination made by Dr Wibel to be a product of the reduction of copper carbonate by the metallic copper of the bronze. Bronzes belonging to this category have often lost their former metallic properties, and if of small diameter have often been completely converted into cuprous oxide, surrounded by a lustrous green or blue crust of carbonates. If a metallic core remains, it is found to be crystalline, brittle, and non-coherent, that is, it flies to pieces under the blow of a hammer. Fine ornamentation and sharpness, whether of edge or of point, have often disappeared. This does not occur with bronzes preserved in water."