Lol, I know because I've not seen a solid diamond shaped ridging in metal. It's always been like a big mesh, (diamonds not filled in) When solid like it appears to be in the photo, I've only seen that in rubber a d usually as floor mats. Still, I've no idea what the photo is.
No mastic, no caulk, just painted metal, maybe slightly worn or chipped paint. It's sitting on the table that you can see in other photos I've posted.
I'm just saying to ignore the background part that looks like this because it's just the table that the object is sitting on. Most of the objects I have posted pictures of were also sitting on this table.
Here is a clue, the diamond pattern area is were you would put your fingers in order to use this item.