Ukontaku (an black engraved print as a feather) (烏金拓)
Ukontaku (also called Ukintaku) refers to a engraved print which is as black as a crow feather. On the contrary, 'Senyokutaku' refers to a light one as a cicada wing.
Since an engraved print was originally born in China to copy down an inscription on a stone monument, basically print was relatively-dark. Later, famous monuments, especially ones whose text or writer was famous, were used as copybooks of calligraphy for good examples. In that case, it was more useful when the contrast was high, so most engraved prints in China became almost jet black.
In the time of the Qing dynasty, when white paper was invented, the engraved print, rubbed by ink stick made from lamp soot until it became shiny, was born. This is Ukontaku. This engraved print, rubbed until it becomes jet black, inevitably stains the object with a little ink through the paper. Repeated prints make the object jet black, and most of the monuments in China are stained for this reason. Today, from a standpoint of cultural property protection, Ukontaku is not recommended.