Peter:

The tarnish you are seeing is easily removed by any acid cleaner that
contains thiourea (and not Hydrochloric Acid).  Most of the chemical vendors
serving the pcb fabrications industry have such a product.  I mention not
using Hydrochloric Acid, because the solder deoxidizers which used to be used
after ammoniacal etching were a combine of Hydrochloric Acid and thiourea.

Rudy Sedlak
RD Chemical Company

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