Fair question! I believe that fine press publishing is in the printing and binding process, and in the details. My books use a variety of printing and printmaking processes to come into the world. They're sewn together with few exceptions, and they are made with quality materials. But the books shine with their details: the illustrations, secrets, construction quirks. The details and materiality are what make these books art. I've made a handy little mind map because that's how my brain works, and some of the terms are expanded upon below.
On more note: a lot of these parameters are less about making the book special, and more about making the book last. Because when you have a book that makes you say "wow" before, during, and after you read, you're going to want to hang onto it.
Lightfast ink: oil, rubber, and acrylic inks are generally lightfast. Laser printing is also quite good. Dye-based ink and conventional inkjet printing will fade quite quickly (a couple of years in occasional sunlight). You know why old bookshelves in sunny spots seem to have a TON of blue spines? It's pretty disproportionate, even? What is up with that? It's because the cyan and black channels on non-lighfast cmyk printing hold up way better than the Magenta and Yellow. Pull out a book from one of those blue shelves to see the colours it was originally printed in on the front and back covers.
Acid Free and Archival Paper: all of the cover paper is minimum acid free, usually archival. If a Carp Dreams of the Milky Way has no digital printing so it'll last forever and ever. All of the digital printing is on acid free bond.
I kind of feel like a jerk for making this distinction, but it's a useful one. Materials are what you use to make something. Materiality is when the materials that you use contribute to your viewers understanding or experience of the thing that you make.
Printing + Printmaking
Printing, is likely what you are most familiar with, xerox, laser, inkjet... you stick a paper in a machine connected to a computer and it comes out looking more or less like whatever is on the screen. Printmaking is what I have a Bachelors of Fine Art in. Printmaking has several subcategories including:
Letterpress, which is a relief-based printmaking involving a large mechanical machine, and a substrate (lino block, wood block, lead type, wood type, polymer plate) that is a very specific height. Uses oil or rubber-based-ink. (all of my fine press books)
Linocut, which is a relief-based printmaking that can be printed with a press or by hand. Involves carving into a piece of linoleum so that the raised parts print and the carved parts don't. Read more about it in Linocut Printmaking 101. (all of our fine press books)
Polymer Plate, which is a relief-based printmaking that translates a digitally-generated image into a plastic sheet with raised and lowered areas.
Screenprinting, which is a planographic printmaking when you use a squeegee to push acrylic ink through a fine mesh with a chemical stencil on it. (If a Carp Dreams of the Milky Way)
All of these fine press books are sewn except for The Size of Texas and The Midnight Garden. The Size of Texas and The Midnight Garden are perfect bound with a machine we had in 2018. You can read about our favourite binding method in Pretty Perfect Paperback Binding.
Illustrations (that aren't just for kids): Adults like pictures, too. (Caterpillar Portraits, The Size of Texas, The Midnight Garden, If a Carp Dreams of the Milky Way)
Marbling: This is a totally beautiful process that I've used to enhance the cover on Caterpillar Portraits. It involves floating a bunch of swirling pigment on some water, and placing your paper very carefully on top of it so the colours transfer.
Hand Drawn or Written Details: We try not to do too much of this because it is impossibly labour intensive. The Midnight Garden has a handwritten note and a kiss on the inside of the front and back covers (all 200 of them).
Rivets: Little metal circles that hold two pieces of paper or fabric together.
Metallic + Embossing Powder: powders that are applied to still wet ink, and sometimes heated so they melt and become smooth. (Caterpillar Portraits, If a Carp Dreams of the Milky Way)