Gold or plate

[Bonsai]

Not sure where to post this it's a follow up from a thread I had about the quartz being a tad loose and I wanted to start a new thread on the gold.
This was sold as 9c, untested. Seller looked through a Loupe to see if there were chips or wear to the gold plating, no.
I've tested it extensively and had a 3rd party jeweler test it.
It's def 14 k

Everything tests positive down to the hinge, except th e inner parts of the front opening.
The outer opening is thin, but the edge of the inner opening, you can see, has a flat area where it meets the inside of the outer piece.

This tests as something not gold.

I've scratched the same areas on the outer bezel prob up to 10x hard on the test stone and they still test as 14 k along with testing as 14 k on 2 different KEe testers.

So...
Is it plated
or
Is the inside lip made of something else?

It seems like, if you look at the right side being as thin as it is that with me scratching the same area 10x I'd have worn it down. I also filed it with a stainless steel file. Same result 14k.

Does anyone have enough knowledge of lockets that would they have used a different material on the inside lip?
I know with my victorian lockets (silver) they have an inner frame that's often not silver and placed around the inside lip for strength. It never tests as silver.
Do they do this with gold also... or would you assume this is plated?

I need to get bak wit the seller. I would like to keep this but not sure on the price I paid if it's plated.The red line area is what is not testing as gold.
This area on the other side, tests as gold.

 

[stracci2000]

I would not be too concerned about the inner ring surface.
Jewelers probably did a lot of things to keep costs down, and this might be an example.
As long as the outer parts and the bail test gold, I would be OK with this.
Since you have some sterling lockets exhibiting the same kind of results, then perhaps it was the standard of the day in locket engineering!
Maybe you can use it as a bargaining chip to negotiate a lower price.

 

[Bron357]

Don’t worry, they always do “moving parts” as steel / nickel silver because gold would end up “wearing away/out ” with movement.
Even with a $100,000 Gold Rolex, the watchband “pin” is always steel.
If there are signs of wear on the actual locket, it could mean its “gold fill” “gold plate”. This is a reasonably thick coating of gold over metal. Unless you can “scratch” deep enough - not recommended though- to see if there’s a different metal underneath, any gold scratch test will test as gold.