The scale that spoke of, I had heated some files with hope of making a knife,. Ihad read that files were being made in Mexico, Brazil etc. And were case hardened. Like you said the scale is very hard. Which further led me to believe it was the carbon outer layer of case hardening. Which after your mention of the scale, I see that my assumption is incorrect. What is the scale? does it come from the knife? Like rust? Would it change weight of the knife even tiny amount? Thanks for your time. The files were what started my interest in knife making. And they made sharp cutting implement be stretching it a bit to call them knives.