Fig. 1

pH versus pE equilibrium diagram of the Fe–S–H₂O system, modified from Garrels and Christ (1965) and Henshaw and Merrill (1980). The pH and pE of the reductive etchant should be adjusted to plot in the Fe²⁺ area. Circle symbols indicate the etchant comprising the ascorbic acid solution buffered with sodium bicarbonate. Triangle symbol indicate the KI solution