1896 photography medal, but what metal is it?

[bagerap]

I've bought this medal. Association Belge de Photographie. Exposition Internationale 1896. Signature looks to be Fernand Dubois, although probably not that of Émile Fernand-Dubois. Altogether a nice little bronze.
Except that on the reverse  there is a nice shiny silver looking patch.
Here is where I'd like someone to check my work and my thinking.
Dimensions in mm, if this were a flat solid:
59.6 x 44.8 x 3.5 = 9.345 cc
Density of silver= 10.49 gr per cc
Piece weighs 84.2 gr.
If it were a solid silver weight should be 98.03 gr, but sterling silver would be 90.67 gr. a difference of 6.47 gr.
This medal is not a uniform flat solid and only on the reverse does a small part of the relief protrude above the height of the edges.
Do I have enough reason to believe that this is sterling silver?
Every example I can trace is listed as bronze, but this is obviously not the case here. And yes I am trying to find a graduate cylinder large enough to try displacement.

[eurocoin]

It is not sterling silver.

[bagerap]

Can you expand on that please?

[eurocoin]

The colours of this patina I do not recognize as that of (sterling) silver. Furthermore the small silver-coloured part is not the colour of silver alloy either. By all means continue your interesting research to find out what it is made off but do not expect it to contain silver. If you can find any ways of having it XRF tested that would be interesting. Displacement is going to be difficult I think as I expect that it is made of some sort of mix of alloys of which we also do not know the proportions.

Regardless, it is indeed a nice and interesting piece.

[bagerap]

There is no patination. It is either silver colour or applied bronze pigment.

[eurocoin]

So you think that what we are looking at here is a chunk of sterling silver on which bronze pigment was applied, with at the patch on the reverse a small part of the underlying silver visible?

[Henk]

The specific gravity is 84.2/9.345 = 9,01

The specific gravity for some metals is:
Copper 8,9
Bronze 8,7
Brass 8,4
Silver .999 10,5
Silver .925  10,3
Silver .835  10,2

Your measured value is closer to copper/bronze than to silver. Measuring volume by size, especially average thickness, is of course quite inaccurate.

As a check you could make a small cut in the edge which will show the underlying metal.

My guess abronze medal which once has been silvered, explaining the silvery patch.

[bagerap]

My initial thought on seeing images of this item was that it could be solder, but on receiving it, the bronze coloured layer is definitely uppermost.
The layer of bronze is pitifully thin and I'm wondering if the silver coloured strata was applied to make it easier to plate.