What’s the difference between gold fill and gold plated?

First I rarely see gold filled pieces made in the last 60 anos. The only pieces I see that are gold filled tend to be estate pieces, particularly “gold” pocketwatches of the 1930’s

In most cases of reputable manufacturing a gold filled piece should be marked .

In most cases of reputable manufacturing gold plated items .

Aside from that you can tell with a trained eye quite easily. Gold plating rubs off quickly and easily. you can take it down with sandpaper in seconds. Likely underneath you will find a soft grey metal. Putting gold plated jewelry to a standard acid test of any carat will immediately dissolve the sample in less than a second.

Gold filled is actually much harder to separate from solid gold than it is from gold plated items. Gold filled items have a shell made of gold; then the middle is filled with crap. A poorly conducted acid test can leave one with the impression that the item is solid gold. To be 100% sure an item is not gold filled one must do substantial damage to the piece in question. A proper acid test cannot be performed unless the item is filed down no less than 1/16th of an in. Ideally you would cut the piece in half and test the core but it can be done with a file as well in a pinch.