How to feed dry leather?

Hide needs occasional feeding to stop it cracking. Most restorers apply a good quality hide food or a microcrystalline wax. Work it in gently with your bare fingers or a soft cloth. Leave the chair to sit overnight in a warm room before buffing off any excess wax.

Can flat horsehair be replaced?

Yes. Traditional upholsterers can strip the seat and tease out the old horsehair. Then they build the layers back up. They're usually keen to save original materials.

I have inherited a set of dining chairs but one of the legs is a bit loose when you sit on it, can that be fixed?

Loose joints often turn up on old dining chairs. The hide glue dries out over a century of central heating and shifting body weight. A cabinetmaker will knock the joint apart. They clean the old surfaces down to bare wood before re-cramping the frame tight. They use traditional animal glue so the fix can be reversed in the future if needed.

Some of the brass tacks around the edge of the seat are missing or stick out and catch on clothes, should I tap them in?

You can tap loose tacks back in. Use a small tack hammer and place a piece of cloth over the head to stop it bruising. If the hole is too wide, the tack will just fall out again. An upholsterer might plug the void with a sliver of wood before driving the tack home.