It seems like the light
weight solidus has a little smaller size than the toher 2 solidii, so it actually could be from clipping.
Gold has density 19,32 g/cm³ and copper has density 8,96 g/cm³.
So if it would be
plated with copper core it should have either about 2 times the size as a real
solidus or 2 times the thickness as a real
solidus.
Or a combination of huger size and thickness for example 50 % huger size and 50 % huger thickness.
It only looks like
red encrustrations on pictures and as written a
plated coin would have huger size and thickness, which I can not see on pictures.
I do not see any reason to suspect it on pictures but pictures are not
good enough for a really reliable authentication.
So you can either make much better pictures including pictures of the whole edge to
search for clipping.
Or showing this coin to dealers or experts of
auction houses for example at coin shows/fairs, it is possible that some will have a look at it for free.
Or you can offer it to dealers or
auction houses, some have the option to upload pictures of your consignment/coins you want to sell and if they want to have or sell it, it is likely authentic and then you will have to say depending on their estimate yes or sorry I hoped for more not interesting anymore in
selling for such a
price.
Or sending it to
Sear or
NGC etc.