I'm a huge fan of Gustav Dore's work, even got one of his pieces on my right arm (Sleeve) and was wondering where would I begin to start drawing similar pieces?
Also, same question about traditional Japanese tattoo artwork, where would I begin?
Usual basics - light sources, anatomy, perspective, etc.
Study his work and look at other printmakers. Hell, take up printmaking if you can, that would help you understand the materials and processes he would/may have used.
Also, same question about traditional Japanese tattoo artwork, where would I begin?