Old jewellery looks like fancy dress when it is worn in the arrangement it was designed for. A matching set, worn as a set, with the hair and the clothing that set was made for, is a period costume. The same pieces separated and put against plain modern clothing are simply good jewellery. So the first rule is to break up anything that arrived as a suite. Wear the earrings and leave the necklace. Wear the necklace with a t-shirt and nothing else. The second rule concerns finish. Jewellery from the middle of the last century was often highly polished, and high polish now reads as formal in a way it did not then. A jeweller can give a piece a softer brushed finish for very little, and it changes the register completely. The third rule is about the neckline. Older necklaces sit higher than contemporary ones, so they want a plain crew or a bare neck rather than a collar to compete with.

The most effective thing you can do with an old piece is put it in a stack with new ones. This is where mixed metals stop being a rule you break and start being the mechanism. A high karat yellow gold heirloom next to a cool white gold band does not clash so much as date each piece correctly, and the effect is that neither looks like a costume. Keep the contemporary pieces very plain when you do this. A textured or detailed modern piece next to a detailed old one is a collision. On practical matters, have an old clasp checked before you wear the piece out. Spring rings and older box clasps fail, and a chain lost in a taxi is the common ending. Earring posts on older pieces are frequently thicker than modern ones and can be uncomfortable, which a jeweller can thin. Screw backs can be converted to posts, and it is reversible.

Wear it. That is genuinely the advice. The pieces that read as costume are the pieces that come out twice a year for occasions, because occasions are where costume lives. A heavy old chain worn with jeans four times a week stops being a period object within a month. What we would avoid is the full-suite approach, where the earrings and the necklace and the bracelet all appear together, because that is the one arrangement that cannot be rescued. We would also gently suggest not polishing an old piece back to a mirror finish. The softness it has acquired is the thing that makes it look real rather than reproduction, and it cannot be put back once it is buffed away. If you take one thing away, split up the set, because a suite worn as a suite is the single thing that makes old jewellery look borrowed.