Eugène-Alain Séguy was one of the most prominent French designers at the beginning of the 20th century. He published many design folios using the pochoir technique – for example his butterflies you can see above. 「Pochoir is a refined stencil-based technique employed to create prints or to add color to pre-existing prints. It was most popular from the late 19th century through the 1930’s with its center of activity in Paris. Pochoir was primarily used to create prints devoted to fashion, patterns, and architectural design and is most often associated with Art Nouveau and Art Deco. The use of stencils dates back to as early as 500 C.E. and was also used in Europe from the 1500’s onward to decorate playing cards, postcards and to create simple prints. It was, however, the increase in popularity of Japanese prints in the middle of the 19th century that spurred the refinement of the use of stencils culminating in the development of pochoir. At the peak of its popularity in the early 20th century, there were as many as thirty graphic design studios in France, each employing up to 600 workers.」
Eugène-Alain Séguy was working in Art Deco and Art Nouveau styles. This butterflies are just a small excerpt from his amazing works. Sources: NYPL and Smithsonian Librarys.