[A. G. Maisey]

Thank you David.

Yes, I'm sure it is old fashioned blackboard chalk.

Chalk used to be made mostly of calcium carbonate held together with other ingredients.

The reason that even old Balinese blades have a smooth surface is that Balinese keris are routinely cleaned with powdered limestone, which is comprised mostly of calcium carbonate.

Calcium carbonate is a very mild abrasive and has a number of applications where it is used to polish away surface stains and dirt.

I do not know what modern chalk is made of but I suspect it might be something other than the old recipe.

Incidentally, Ballistol is a pretty effective polish for silver & brass.