Overprinting practice blocks
See "Japanese Print Making" by Toshi Yoshida and Rei Yuki, © 1966, Charles E.Tuttle Co, Inc, Chapter 11, Effects of Overprinting, Pages 131 to 136.
The book illustrates some of the effects which can be made by overlapping colors from two blocks, one printing a solid oval shape with a non-printing circle inside, and the other printing a solid rectangle with a non-printing square inside. The non-printing interior areas are arranged so as to half overlap when printed on a single sheet. Two-color prints were pulled from these blocks and reproduced to show how water color and gouache printed with each block produce different results depending on printing order, opacity, etc.
Years ago, I practiced with a set of these blocks. My oval block was carved from some grainless veneer on composition board and my rectangle block was from lauan, a mahoganey like wood with a pronounced, usually straight grain.
Here are the block designs and a few of the prints I made from them. The paper was student grade (cheapest variety) Hosho. The pigments were inexpensive watercolor and gouache from tubes. The brushes were horsehair shoe brushes with very few bristles (not nice ones at all).
The rectangular block with kento (little 'seats' for the paper to sit in for registration purposes). The gray areas in the middle are the ones which print.
The oval block with kento (little 'seats' for the paper to sit in for registration purposes). The gray areas in the middle are the ones which print.
Rectangle block printed in transparent blue with bokashi (gradation) on one side. Oval block printed with ochre with Chinese white added for opacity.
There were at least two printings of each block -- three of the oval block using transparent watercolors. The Red on the oval is a cadmium red light which tends to be more opaque.
Several printings of each block in various colors. The first printing was of the magenta colored oval. Both paper and block were too wet, as you can see on the left side of the interior circle where the magenta has 'bled'.
Another print in which the oval block only was printed at least five times, probably more.
Hope this helps...