Rust-proofing chrome-plated steel

Chromium plating is porous. Anything that effectively blocks the pores helps. There have been many recipes, usually consisting of some sort of wax or grease and a solvent. Such as white spirit and vaseline. Allow to dry. Repeat. Finish with a coat of good wax polish (maybe risking a car polish). Repeat wax occasionally. Others may well come along with their own, and possibly much better, ideas.

Spray it with a clear lacquer of some sort. Holts do (or did) a car body protector spray aerosol that might do what you want.

If you're lacquering metal (esp. brass, to which nothing wants to stick) then you're best going straight to a methacrylate lacquer specifically for metals. Few quid for a small bottle. Rustins do one, Axminster sold it last time I looked.

Really though, stainless is the way to go here. Otherwise nickel plate, rather than chrome. Looks nicer (IMHO) and is effectively impermeable, in the way that chrome isn't.

Think on a good job, nickel is used underneath chrome for this very reason.

On old chrome plated steel I've seen the underlayer appears brass/copper colour, nickle is a "white" metal is it not?

For a possible solution to the OPs problem how about "Chrome Cleaner" as one would use on a car bumper when they where nice tough bits of chrome plated steel rather than large expensive and weak plastic mouldings.

"Triple chrome", which is very rarely done these days.

Copper goes on first, because it's cheap, dead easy to plate and you can polish it smooth more easily than the substrate (usually steel).

Then nickel, because it adheres well, is impermeable, and is also fairly easy to plate.

Finally chrome because it's shiny but is otherwise utterly useless as a plating material. It's only platable from cyanide solutions (vapour hazard, whereas most plating baths are only acutely toxic if you drink them), doesn't stick worth a damn (nickel is a little better as a substrate, but directly to copper is poor) and plates so slowly and badly that it has to be done as a really thin layer, so it remains permeable.

"Hard chrome" (hydraulic rams and machine gun barrels) is a different process to shiny, polishable, decorative soft chrome. That has its own problems, but at least it's thick and hard enough to provide a robust layer.

For plating onto flexible non-conductors (baby bootees etc.) it's good practice to alternate layers of nickel & copper. This can look like either, according to which you stop with, but the layering makes it much stiffer and stronger.

IIRC, the most durable chrome plate on steel goes brass first, then nickel then chrome.

That certainly keeps the steel well away from the chrome. Isn't the problem with chromium on steel that the chrome stays shiny because the steel acts as a sacrificial anode that protects the chromium?

Thank you everyone for the ideas - I'll give the spray lacquer a shot and see how we get on.

That may well end up being the best long term solution. I'll keep an eye on out for what's available in a similar design/size.

Thanks again,

Mathew