This is the Stillman & Bern Gamma series, hardback, 14cm x21cm or 5.5 by 8.5 inches.
The description says “Dry media, Light wash, Ink”.
I’m using it for quick watercolours. The pages crinkle a bit, which troubled me at first, but I got used to it. They straighten out if I clamp it with bulldog clips.
The pages are a pleasing ivory colour and smooth, not shiny and not cold press. It’s cartridge paper, very strong, with “tooth”.
A good chunky feel, 62 pages and about 2cm thick.