The plates that these prints are made from started life as electro-etch test pieces. They are all made from electro-etched aluminium. It is a soft metal that etches deeply and in the areas of open bite provides a tooth that holds ink really well. Peter Wray, in his article on saline sulphate etching in Print Making Today, describes it as a natural aquatint. Although aluminium is soft the depth and quality of the etch achieved with electro-etch appears to hold out really well against the pressure of the press. I have plates that have been through the press thirty times with little effect on the quality of print obtained.