Why copper tungsten has different color?

Some of our customer has doubt when they received our copper tungsten alloy bar, rod, or plate. They don’t know why the product color totally different compare to the last delivery? Or why the products color different compare to the other supplier’s product? Is anything wrong? Below is our explain:

copper tungsten rod-yellow

copper tungsten plate - yellow

Above pictures show copper tungsten light yellow color. Those rod diameter bigger then 20mm, it is machinery by lather. The lather tools bring the copper cover the surface of rod. So the rod looks like coppery, it does not mean the tungsten composite less.

copper tugsten rod- graycopper tungsten- dark gray

Above picture shows dark gray color. This rod diameter smaller than 18mm, it was machined by grinding.Grinding process working with the coolant liquid. And it will eliminate the copper particle. The dark gray color does not mean it has more tungsten composite.