Sites like Azbyka.ru and Pravoslavie.ru often host free, legal PDF versions of classic theological and technical texts on iconography.
If you want to "read" an icon—understanding its symbols and theological meaning—these are the best starting points: ikonopis kniga skachat
A detailed look at the "hidden" techniques of ancient masters. Sites like Azbyka
A comprehensive overview based on the British Museum's collection, covering the development of iconography across different nations and eras . ikonopis kniga skachat
A highly visual guide that breaks down the layered process of tempera painting. History & Art Theory
Finding quality books on often involves choosing between historical overviews and practical technical guides.
For the latest editions and high-quality e-books (EPUB/PDF), Litres is the primary source in Russia.