Such is the leitmotiv, more or less, of the processes for obtaining the green or brown-green patinæ. Some dip the object in cupric acid and then place it in a room in which an excess of carbonic acid is produced, by others preference is given to one or the other element according to the tone and colour desired. Brass articles are coated with green patina by a solution containing 150 parts of vinegar to which has been added ten parts of copper dissolved in twenty of nitric acid. An application of this liquid is generally made on the object. The brown patina usually characterizing old medals is obtained in many ways. One is by heating the medal at the flame of a spirit lamp and then brushing it with graphite. To colour a number of medals at the same time, some imitators dissolve thirty parts of verdigris and thirty parts of sal-ammoniac in ten of water, adding water to the solution till a precipitate is no longer formed. Then the medals are placed in a shallow dish without touching one another and the boiling solution is poured over them. The medals are allowed to remain in the solution till they have acquired the desired tint, which should be a fine brown. Green or bluish patinæ may also be given to bronze or copper by triturated copper carbonate used as a paint with a pale spirit varnish, shellac or sandarac, and applied with a brush. Verdigris generally gives a bluish tint and crystallized verdigris a pale green tint. The two tones can be mingled to obtain some special hue. Iron work is perhaps one of the easiest to imitate and give an appearance of antiquity. As far as the actual work is concerned, it rests entirely upon the skill and artistic taste of the worker. Patina on iron is either caused simply by rust or by a slow process of oxidation which confers a rich, dark tone to iron. There is also a special patina seen on iron that has been under water for a long time, but this is rare in imitations and very difficult to obtain. The rusty coating on iron can be produced by almost any preparation capable of oxidizing the surface or transforming it into basic salt provided a red colour results, as with nitric or hydrochloric acid, for instance. The brown patina is often obtained by oiling the piece and exposing it to the direct action of flame. The two methods may be alternated and the corrosion of the acid here and there adds character to the piece. Methods are so various, however, that the way to obtain a convincing patina is perhaps contained in the dictum of an Italian antiquary: “To inflict upon the object that is to be turned into an antique every possible indignity and abuse.” The patina in imitations of old iron work is so well reproduced nowadays that even experts are unable to distinguish the real from the unreal with certainty, so much so that more than one has had recourse to an analysis of the composition of the iron in order to decide whether the object were modern or antique.