A loose chair is the most common — and most fixable — problem in any secondhand haul. You need less than you think.
Nearly every wobbly chair that comes through here has the same fault, and it is almost never a broken part. Old animal glue simply gives up after fifty or eighty years, particularly in a centrally heated house. The joint is fine; the bond isn't. That distinction is the whole job.
Work the joint apart gently — patience, not force, and never a hammer against bare wood. Clean the old adhesive back to bare timber with warm water and a scraper; fresh glue will not bond to a layer of dead glue. Dry-fit everything before you commit, because a joint that doesn't close dry will not close wet.
There's a line between honest wear and neglect. Restore function; leave the story. A century of hand-polish on an armrest is worth more than any refinish, and stripping it is the one mistake you cannot undo. Structural failure gets fixed; evidence of use gets left alone.
Hide glue is reversible. Whoever repairs this chair in forty years will be able to take the joint apart the same way you did. Modern woodworking adhesives are stronger than the timber around them, which sounds like an advantage until the next repair splits the wood instead of the joint.
If you spend long enough matching hardware and finishes, you start noticing the same work in films — the furniture, the felt, the light fittings chosen to date a room precisely. There is a good piece on how period rooms get dressed on screen, and it changed how we look at reference photographs.
New to it? Start with the beginner's kit.