Book  (Apr 1993)  Page(s) 165.  
 
Etna Hybrid Tea, deep crimson-maroon, 1924, 'Red-Letter Day' x 'H.V. Machin'; Looymans. Description.

Book  (1936)  Page(s) 244.  
 
Etna (HT) Looymans 1924; Red-Letter Day X H. V. Machin; dark crimson-maroon, large, semi-double, cup form, lasting, in 2-4s, floriferous, continuous bloom, growth 6/10, upright.

Website/Catalog  (1925)  Page(s) 26.  
 
Etna (HT) (Looymans) Raised from ‘Red Letter Day’ x ’H. V. Machin’. A semi-double variety of a deep crimson maroon colour. Large flowers with petals of good substance, opening flat; a strong grower, flowering freely. Recommended for bedding, massing and decorative purposes. 4/- each.