The inserts from Sandvik come sharpened on both sides, but a person may want to change the radius, usually to something of a smaller radius for finer spotting, also I keep a insert that is ground nearly flat for scraping rust off way surfaces. The best thing for sharpening is the Glendo lapping machine, next in line a carbide grinder with a diamond wheel, then the green wheel. When I started scraping, about 56 years ago, I started out using Dykem (Prussian) blue, then after doing some reading in the Machine Tool Reconditioning book, started using red lead in oil, kept in a paper snuff box; you mix it well with a minimum amount of oil, press it into the box, and the box wicks the excess oil, for use put in a few drops of oil and rub it in with the fingers and transfer it to the marking tool and rub it into the surface, and piece of grit or forigen matter can be felt and rubbed off. I have the Canode that Rich K. gave me and it sure is a lot easier to clean off than any other medium, and I like using the yellow for background on the article being scraped; it is applied very thinly and mostly rubbed off, it makes the blue medium stand out much more clearly when rubbed off the marking tool.