wondering about chalk and tarnish as well. I remember finding a
piece of blackboard chalk in one of my grandmother's jewelery
boxes and wonder if she put it there to keep the silver from
G'day; The 'chalk' used by dressmakers is not chalk, calcium
carbonate, but is talc, which is also soapstone.
It certainly won't stop sterling from tarnishing, and I doubt
whether calcium carbonate will either
Blackboard chalk is often a mix of calcium carbonate powder bound
with slaked lime; calcium hydroxide, or sometimes calcium sulphate.
Cheers for now,
@John_Burgess2 of Mapua, Nelson NZ