what would 19 on the hand held rockwell tester conver to?

Which handheld -- the Ames? That one (which I have one of), IIRC, is made to measure purely Rockwell C scale. And for something that thin, you want a Superficial scale instead, which requires a different indenter, and a different maximum pressure. Predicting what it would be is beyond my capability -- there is a reason that hardness testers are made with separate scale capability -- conversion between Rockwell C and Superficial when the thickness of the material pretty much demands superficial is not a simple matter of looking up a table.

Good Luck, DoN.