Australian artist John Lovett has a great article on his website about different kinds of sketchbook-keeping. Aside from using sketchbooks to capture ideas and practice drawing, he talks about using a notebook or sketchbook in the studio as a working book, for recording technical stuff about materials and methods:

Artists Studio Notebooks

I always have a working notebook in the studio where I test out new colors, experiment with color arrangements or write down little things I want to remember about the behaviour of different materials. These become a handy source of reference – especially years later when ideas and experiments are long forgotten. They don’t need to be attractive or carefully planned – just a way of preserving and keeping everything together. 

He says they don’t need to be attractive, but these pages can be beautiful, as seen in his example above!

Read more: Artist Sketchbooks and Journals | John Lovett Artist