Originally Posted by ubeaut
Urban and others - Talc is Magnesium Silicate Hydroxide. Yes it is also known as French chalk but this can be a bit confusing, as Chalk, also known as whiting, is actually calcium carbonate and there is a big difference.
You can use talc in a mix as sanding sealer as it is translucent and as a rule won't leave white in the grain unless you use way,way, too much or use the regular stuff from the shops which may actually contain some chalk.
Chalk on the other hand will act like a paint and will blanket out the grain of the timber.
Cheers - Neil :)