The essence of Table 3 is not of simply listing Escher's 137 periodic drawings, but rather that of determining what Escher did to border his tessellations, or otherwise. On occasions, he chose not to have a border line, with the edges of the tile determined by colour alone of the motif. Ideally, this would be a simple listing, but various factors militate about this:
Revised working, where the revision has obliterated the original e.g.No.54, of October 1942 and April 1963
'Instructional' tessellation, e.g. 136
Imprecise outline
The following key applies:
Colour. Motifs defined as by their colour alone, without an 'extraneous' border line. Included in this category are black and white
Outlined. Motifs with a decided outline (albeit of different thickness), with a black line by default, with occasionally a different colour, as stated
Unclassified. Occasionally, it is not possible to place easily into the above categories. These I term as 'unclassified'.
2 Of different thicknesses