The adhesive used in most aspects of violin making is hide glue. It is made from the connective tissue (skin bones, tendons,etc) of animals. Hide glue has been in use for many thousands of years, although it is not as commonly used today. It is a good glue for violin making because it can make both very strong joints and weaker, easier to separate joints. The joints don’t creep like joints made with modern aliphatic resin glue often do. A well made joint doesn’t show a glue line, and hide glue is easily cleaned up with water. This is particularly useful for making repairs.
When I worked in a repair shop, the first person to arrive each day would have the job of turning on the glue pot and making new glue. You wanted new fresh glue for some tasks- like reseting a neck, fixing a crack or gluing in a bass bar but older weaker glue was better for joints that were meant to come apart eventually like glueing on a fingerboard or a top.
Hide glue can be stored in its dry, granulated form indefinitely. When you need some glue you mix it with water and heat it. It is a gel at room temperature so it has to be warmed to around 140 degrees F to be used. It has a short “open” or working time because it starts to gel as it cools. Consequently, it is difficult to do a long complicated glue up with it because you have to work very fast. It requires a relatively long curing time (12-24 hours) under clamping pressure for the strongest joints.
Modern aliphatic resin or white glues by contrast, work at room temperature; have longer working times, but then set up much more quickly, often only needing to be clamped for an hour or so. Hide glue has been largely replaced as a go to adhesive for most other wood working by these modern glues, not because it doesn’t work well but, because it is harder to use and is less forgiving to casual users.
I bought a big tub of hide glue many years ago and have been, for the most part, happily using the same glue ever since. Recently I have added some new animal glues to my arsenal. Fish glue is very similar to hide glue and is compatible with it, but it stays liquid at room temperature and has a much longer working time. I have started using it to glue ribs to corner blocks and to glue in linings. Both are jobs where you really benefit from having more working time. I was a little concerned about the strength of the joints but fish glue seems to be even stronger than the hide glue I have been using. A colleague recently introduced me to bone glue. Bone glue makes a weaker joint than traditional hide glue, but otherwise is quite similar. It needs to be heated like hide glue but its weaker strength makes it a good candidate for gluing on tops and fingerboards, that you might later want to take off.