For blackening carriage ironwork, japan of two kinds is employed; one kind is known as baking-japan, and is hardened by heat, whilst the other dries in the open air and at ordinary temperatures. Baking-japan is made by melting asphaltum, removing it from the fire, and stirring in oil of turpentine; its effects are permanent, and it does not need to be varnished; such a protection is necessary for ordinary air-drying japans. Small work that has become dull by storing is dipped into the japan, the surplus is drained off, and the work put into an oven, where it is maintained at a temperature of several hundred degrees Fahrenheit for some hours. Fine work should have a coat of dead black colour first as the japan is transparent, and in this case may be applied with a brush. The air-drying japanis a jet black solution of asphaltum in turpentine; it is brushed on and dries quickly, but does not become so hard as the baked japan, but it may be recommended for parts which are not handled much. An alternative method of blackening iron is to employ ivory black ground in brown japan. This is made up to the consistency of butter and is thinned with turpentine, being applied then with a small camel-hair brush. It dries in a few minutes, and should then be varnished.

When work is wanted in a hurry, quick-drying French shellac varnish may be used. For cheap work, lampblack and shellac varnish will do admirably, but asphaltum, of course, is to be preferred. Japan may be applied to small articles by means of 1-in. flat badger bass brushes having tin ferrules. When working, it should be borne in mind that all japans are partly transparent, and that when one coat over a bright metallic surface does not cover satisfactorily, a second coating must be applied; care should be taken that the first coat of japan is quite dry before applying the next, or rough, dull work will result.