In relief printing, a reduction print is a multi-color print in which the separate colors printed from the same block at different stages.
Reduction, in this way, is “cutting” the printing plate to block the surface from touching the ink. Usually, the lightest color of the design is printed first, then the block is “reduced” by carving to the areas which the artist wants to print the second color from, and so forth.
For example, in my project, I planned my still life to be printed on white (paper itself), yellow, turquoise and orange.
First-time printing: white on yellow. Firstly I “carved” the white part of the design and applied yellow on the whole printing plate. Therefore, the hollow part never touched the yellow. Similarly, I carved parts that should be yellow in the design and applied turquoise in second-time printing to keep the yellow apart from turquoise.
The disadvantage of reduction printing as opposed to printing from multiple blocks is that once the first color is printed, the matrix for it is destroyed in the creation of the printing matrix for the second color. In this case, the turquoise turned green and orange turned brown as layers overlapped others.
It is impossible to undo mistakes.
In my experience, so brain squeezing is this technique. It requires lots of concentration to understand the logic of overlapping colors and creativity as the design can be continuously created and amended along the way printing.