I use dish soap on mine too.  Just make sure to rinse it well.

I have a stone one (not jamie's) and i always put mine in the dishwasher. Not sure if this is the right thing to do but Ive been doing this for years and no harm has come to it. 

Thanks everyone for the responses. I guess I'll wash it up then!
Cheers
Briony

Dear Briony

The care guidelines for Jamie's black granite pestle and mortar are
handwash only in warm soapy water. Rinse and dry thoroughly.
I have also included some tips and advice from Jamie at Home on using it, enjoy!

Gena x
Jamie at Home Ambassador


Made of polished and unpolished black granite this item is
timeless.  A pestle & mortar is one of Jamie’s essential kitchen prep
items, as noted in his books. The large pestle allows your hand enough room to bash, mash and grind your spices without crushing your fingers too.
You can make quick, no fuss curry pastes, marinades or a fabulous basil pesto.
Be careful not to overfill your mortar, it is designed to crush about a tablespoon of spice at a time, even though it could hold a lot more.
For garlic and herbs, pound them to get a nice aromatic paste; with spices the most
effective technique is a circular grinding motion, keeping the pestle in contact with the
mortars surface at all times.