As best I can tell, most artists of that genre nowadays produce digital images. Graffet, however, seems to have mostly or entirely painted using acrylics. That is more laborious than digital, given the amount and type of detail he uses. But the result is something tangible that can be sold for a good price, if auction values for some of his works are any clue.
Below are examples of his paintings found on the Internet.
First, to place Graffet's work in context, a fine example of digital Steampunk art by the well-known Stephan Martinière.
Trafalgar Square, London. HMS Victory sits by Nelson's monument while a huge dirigible loiters overhead. The people are dressed as in the 1890s.
The train station for points north of Paris. The façade is there, but far, far above street level. The sign fragment at the upper left advertises trains for London.
Eiffel Tower as seen from across the Seine. Some of the airships are steam powered, highly unlikely in reality, but found in Steampunk illustrations by other artists.