BGE Aesthetic Artworks - They used a "Decalcomania technique" its the process of applying gouache to paper or glass then transferring a reversal of that image onto canvas or other flat materials.
Decalcomania Demonstration Video - YouTube
Abstract Decalcomania Contemporary Art NYC | Paul Kolker Contemporary Artist New York
Decalcomania Painting Art Exploration | Inquiry Based Learning Lesson Plan - Art Sprouts
Lazy Nerd Explainer: Decalcomania Art is a Hot Mess