Here's how to do it:
1. Tear a scrap of paper that is at least as long as your card. This will be your mask.
2. Lay the torn edge along your card where you would like your faux tear to be
3. Use sponge daubers and your inkpad to sponge along the torn edge
4. Move the mask up over the sponged edge a few mm and stamp or sponge the cardstock above the tear
Here I stamped with the Paisley Background above my faux tear. The colours I've used here are Bashful Blue, Brocade Blue and certainly Celery. The "Merci" Sale-a-Bration set is so lovely to watercolour!