 From the mid @-@ 1870s Busch 's illustrations were printed using zincography . With this technique there was no longer any danger that a wood engraver could change the character of his drawings . The originals were photographed and transferred onto a <unk> zinc plate . This process allowed for the application of a clear , free pen @-@ drawn ink line , and was a much faster printing method . Busch 's use of zincography began with Mr. and Mrs. Knopp . 
