I have played on a standard yamaha 11B4 mouthpiece for years on my intermediate trumpet. However, I am after a darker, fuller tone- I heard a deeper cup gave this affect. Could anyone suggest a specific brand or shape to try out?

Much thanks

It is true that, other things being equal, a deeper cup gives a darker tone. Try having a look through this Brass Forum page. You will find enough info to keep you confused for days ....