I used bark tanned calf skin for the cover - it has a relatively fine grain, is smooth and strong and has a nice colour due to the chesnut bark used. The leather was cut to size and the part of the leather that will be folded over the edges of the boards was thinned using a paring knive.
Here you can see my little glue pot - its just a small period mug that I use to warm the animal glue on a little stove. Animal glue is only usable when warm and quickly cools down to a kind of jelly. I like working with it, you have to be rather quick or work only smaller areas at a time, but as there is not so much water inside the glue it does not soak through leather or paper. Some people say that it smells bad - but in my experience that only occurs when the glue pot is used over several days without cleaning. After all, animal glue is a feast for bacteria as long as its not dry... Once dried, it stays strong yet flexible for decades (even centuries).