A rouge for polishing metals is obtained as follows: Sulphate of iron is to be heated in an iron vessel over a slow fire and continuously stirred with an iron spatula until it becomes dry and assumes the form of a pale, greenish-yellow powder. Crush this powder in a mortar and sift same. Then calcine it in a new crucible and give it an exposure to the fire of a smelting stove, as long as it continues fuming. As soon as vapors cease arising from it the contents of the crucible may be left to cool and then they will look like the rouge employed in the polishing. The color of the resultant rouge may range from pale red to brown-red, or may be blue and violet. These varieties, however, are caused merely by the different degrees of heat employed, and it may be laid down as an axiom that the higher the temperature during the process of manufacture, the darker the color of the powder and the harder it will be. This is also the explanation of the reason why the violet powder is employed for steel, and the pale red powder is only used for silver and gold. Questions of color aside, it is vitally essential that the rouge be well bruised and washed in water before its employment. To do this you take three glasses and fill one of them with clear water, in which a little rouge is mixed by stirring it a minute or two with a little piece of wood. After the rouge has been allowed to settle to the bottom of the glass (the time being about 1/2 minute) the remainder of the liquid is decanted into the second glass, but every particle of the deposit is to be left in the first one. This identical process is followed for the second and third glasses, but there is this difference: The powder in the second glass is allowed to settle fully two minutes, while the powder in the third glass is left for two or three hours, which is the time required for the assumption by the water of its natural clearness. The sediment in the first glass is of no value; that in the second, of medium quality, while that in the third is very good and can be very advantageously employed after it has been slowly dried. In some cases this rouge may be mixed with grease, and as a general rule found quite advantageous to wet it with spirits of wine and burn it in a clean iron vessel.