In Joe's spirit of serious application to task, aka mucking around on the web....

My two bob's worth (or 2 cents, to satisfy our N. American 'allies'):

Squirt some thin stuff into the crack and asap switch on and sand with coarse paper. That forces the dust into the crack and makes the mix.

Yep, stand aside to avoid fling; and watch out if the crack runs right through.

On light coloured timbers the line will be obvious. ('Natural figuring sir, that's why it costs more than the other pieces').