Etching
There is no evidence that the Vikings knew how to etch metal, but the results are very similar to the other techniques described here. Consequently, etched fittings are acceptable, as they bring the relief working technique into the hands of almost everyone. However, etching requires some rather dangerous acids, so please take care!
Sketch out your design on the work and paint the design on with a thin paint brush, remembering that the painted items will be untouched by the acid, but the unpainted areas will be eaten away, i.e. they will be areas of low relief.
When the paint is dry, build a little 'wall' around the work out of plastecine and pour in the acid. For non-ferrous metals circuit board etching fluid is best, (this can be bought from electrical component stores). For steel, a stronger fluid such as sulphuric or nitric acid will have to be used, (the former can be bought from garages, the latter is difficult to get hold of, try your local school or college).
The depth of etching will depend on how long the acid is in contact with the metal – a few hours should suffice. Do not leave the fluid on the metal too long, or it will eat its way right through! Finally rinse the acid off the work and flush with running water to purge the metal of the acid. Decorate and polish as described below.