Chrome plating: question for the chemists/physicists

[Gsinill]

Apparently it is not possible to chrome over existing chrome.
Now, and this might be a silly question, what makes a layer of chrome "existing"?
If I start chrome plating on a part that has only a layer of nickel, through the electrolytical process thin layers of chrome will be added cumulatively.
So generally speaking, new layers are added to an already "existing" layer as long as the electrolysis is going.
What is different when this process is interrupted and another chroming process starts?

I get it that some metals oxidize so quickly, that is impossible to add to it after the initial electrolysis, but chrome?

Kinda on topic since I am finishing up my lugs as we speak...

[Cicli]

Chrome is the protective coating and is transparent. The polished copper and nickle is what gives it the shine. If it needs to be replated there needs to be the right progression. Copper, polish, nickle, polish, chrome to protect from dulling.

[Gsinill]

Originally Posted by Cicli

Chrome is the protective coating and is transparent. The polished copper and nickle is what gives it the shine. If it needs to be replated there needs to be the right progression. Copper, polish, nickle, polish, chrome to protect from dulling.

Sorry but nope, just did a penny with only a layer of chrome, no nickel.
Not that you should, but you can chrome over copper directly.

[Mike V]

You can reverse your current to etch but you may remove the existing coat of chrome in the process. Then you are worse off.

The "silver" finish is the blue coming off the nickel that the yellow tint of the chrome lets through. The shine is the polish on the nickel. So yes it is transparent. That is why it has depth.

In order for you to "build up" chrome you must nickel, polish, chrome only in the area that is missing. The hard (nearly impossible)part is not effecting the existing chrome.

The short answer is it is best to start from scratch. That is why most don't attempt to "spot plate"

[Cicli]

Originally Posted by Gsinill

Sorry but nope, just did a penny with only a layer of chrome, no nickel.
Not that you should, but you can chrome over copper directly.

Ok,
Chrome dosent give you the lusture without the copper and nickle. And alot of polishing and finishing before the chrome is applied. You cant chrome over a alrealy chromes surface and have it come out right. Chrome finish is the last in a long plating and prep process.