But it was the black edge stain that made me pick it up from the shelf. The publisher describes in its blog why edge staining, once common for mass market paperbacks, is difficult to produce today.
Here is what a May 1942 article in Quill & Quire (Vol. 8, No. 4, p. 24) has to say about edge staining for a new paperback imprint from Wm. Collins Sons & Co. Canada Ltd.
"The edges of the first few [White Circle] books were brush-stained with colour. Then a method of spraying them was discovered, which eliminates any untidy fringes of ink running down into the margins."
Collins used green (though different shades, some bluer than others) and red until 1944 then red only until the end of the imprint in 1952. A few books such as The Riding' Fool were published with both stains.
White Circle 80 - 1943
White Circle 80 back