kostj

On 9/8/2021 at 2:02 AM, gmarguli said:

A quick acid dip will turn many red copper coins to gray.

Brass does not turn to gray. Check out the photo from the last post. 

On 9/7/2021 at 11:25 PM, RWB said:

They have a different color... CuNi will look like a 5-cent nickel coin in color. Also, the density will differ. The density of Cu 75 Ni 25 is 8.95; common brass, Cu 80 Zn 20 is 8.59 g/^3 cm.

The difference in density is very small.
The density of 5 centavos 1965 Cu 75 Ni 25 is 8.92; brass, Cu 85 Zn 15 is 8.66 g/^3 cm.
The difference is near 0,01 g for coin. I don’t have such precise instruments. 

Check out comparative photos. 

Thanks. Your color correction is wrong. The coin looks the same as on the display i.e. look like a 5-cent nickel coin. CuNi and brass coins have weight 4 grams. Different catalogs specified diameter both coins 20.4 - 20.5 mm.
How can density be determined? 

The problem is the brass and copper-nickel coins have the same weight, diameter and edge.

Hello, Is it brass or copper-nickel coins?