How to brighten up plated nuts and bolts?

I have a handful of plated nuts and bolts (I assume zinc) that are yellowish/gold in color that are kind of tarnished/dull looking. I'd like to try and get them looking bright again. Is there something I can soak them in that will brighten them out without damaging the plating?

A quick soak in EvapoRust will brighten them up. Maybe 10-15 minutes.(you can experiment with different times) The zinc is looking tarnished because it's doing the job it was meant to do. The zinc is a sacrificial coating. It's being eaten away instead of the fastener. I'm not sure how long the brighter appearance will last once you remove it from the EvapoRust. It just depends on how much zinc is already worn away and how much is remaining on the fastener.

Metal Polish or lime juice.

A local plater may be able to redo the zinc plating, or there are DIY kits available to do it yourself.

that will both brighten, and replenish the zinc coating.

Soak them in pine sol for a bit.

Its not as aggressive as evaporust or carb cleaners

The way your yellowish/gold parts were originally processed was (1) zinc plate, (2) brief dip in 5% muratic acid and (3) dip in yellow sodium dichromate solution. If the zinc plating is still intact, all you have to do is repeat steps (2) and (3) to get back to the exact original appearance. Muratic acid is cheap and readily available. 1/4 lb of powdered sodium dichromate is about 14 bucks delivered from eBay.

Follow the steps written up in forbbodiesonly here except skip the zinc plating. But DIY zinc plating is relatively easy. I sell pure zinc on eBay for zinc plating.

You could prep the parts by degreasing and hand wire brushing while wearing rubber or nitrile gloves to avoid any fingerprints. Degrease again and rinse after wire brushing. Power wire brushing could be too harsh on the zinc plating.

A good video is here.