Vincent is that a piece of granite I see setting there and what do you use it for. It might even be a piece of carpet pad except for the shine. "Duh".
There was a comment about rivet size. actual skin rivets on a full size plane have a 1/8" shank and a 1/4" brazer head which are very shallow, for 1/4 scale the head is 1/16", they will look fine on a 1/5 scale sport plane, on a war bird it would be best to use scale to size vinyl rivets
Leroy