Even etching is not necessary. 
Usually one can see both intermetallic layer quite nice. They have different shades of gray.
If this is not clear enough, just polish at the end with soft cloth and 0.25um SiO2 for some seconds ( 30 or so ) and clean on the same cloth with water. Pressure approx. 1N. 
The differences in hardness give beautiful structured surfaces. To enhance the contrast one might use DIC.

I attached a JPG picture. Beauty isn't it?

Have a great day 

Guenter

Guenter Grossmann
Swiss Federal Institute for Materials Testing and Research EMPA
Centre for Reliability
8600 Duebendorf
Switzerland

Phone: xx41 1 823 4279
Fax :      xx41 1823 4054
mail:     [log in to unmask]

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