When I used to work as a legal assistant I used to use a trick to make the notary, corporation, court clerk and secretary of state seals stand out on documents before photocopying them. You could try a similar procedure. Since the lettering, dates etc. were raised and embossed onto the paper I would take a pencil on it's side and lightly brush it over the seal to make it more visible.

You could take a regular #2 pencil, (Graphite) and scrape the point over a piece of paper. This will give you some of the black graphite in a powder form. Sprinkle that on the face of the chip and using a soft paint brush, brush the dust into the design. Use a soft cloth and lightly clean the face while working the graphite into the design. Remember to work flat against the face of the chips and not to use too much pressure so you are cleaning the high parts of the chip and not cleaning the black out of the groves or engravings. If you use too much pressure you will work your cleaning cloth into the grove. That will defeat your purpose. You might even be able to take the sharp point of a pencil and work it through the design lightly, wiping away the excess from the surface as you go along.

Good luck