Cockerell is especially known for his skills as a fine binder. The Killam Library at Dalhousie University here in Nova Scotia, has a collection of about a dozen books bound by Douglas Cockerell which I was able to see firsthand last week. There is a digital exhibit on the library's website with really great photos, better than any photos that I'd be able to take, so, have a look at the online exhibit at digitalexhibits.library.dal.ca/exhibits/show/cockerell/ which has multiple photos of each book as well as information about Cockerell's life.
Of course, Cockerell's bindery also developed a distinct style of marbled papers that have been used widely by binders around the world. Cockerell, and the others who worked with him, developed their own style and techniques for marbling that allowed them to produce high-quality marbled papers, replicating their patterns with ease, which is incredibly difficult to achieve with hand-marbled papers. There is a video available showing the Cockerell marbling process, where you can see how they manage to get consistent patterns every time: https://youtu.be/Vyga8VMWXKg. And here are a few pictures of the marbling on the books in the Dalhousie collection that I saw last week.