Source : Webster's Revised Unabridged Dictionary (1913)

Assayer \As*say"er\, n.
   One who assays. Specifically: One who examines metallic ores
   or compounds, for the purpose of determining the amount of
   any particular metal in the same, especially of gold or
   silver.

Source : WordNet®

assayer
     n : an analyst who assays (performs chemical tests on) metals