While both brothers usually share equal credit, it is understood that most of the colour illustrations and detailed monotone images were prepared by Reginald Knowles who signed "RLK" (e.g. : Everyman's Library).
The work of the Knowles' brothers drew influences from Art Nouveau, Victorian Fantasy and Gothic Revival imagery.
A decade after their earliest work, Horace Knowles produced a stunning and comprehensive suite of colour and monotone illustrations for Peeps into Fairyland (1924).
He also illustrated the inside cover and title page of the 1933 memorial edition of The Book of Simple Delights by Walter Raymond.
Legends From Fairy Land[1] Norse Fairy Tales Old World Love-Stories My River and Some Other Waters Angler's Almanac: Some Leaves On A River There is an article & full bibliography by Martin Steenson in Studies in Illustration no.73 published by the Imaginative Book Illustration Society www.bookillustration.org