Dirty or clean.....
How do you strip? I have heard and read both ways ( don't know where or when so please don't ask). My thought would be clean as to not allow excess diet and bacteria into pore. But wouldn't you open it up anyway.
It is preferred to hand strip on a dirty coat, as this allows for a more natural traction/ grip on the hairs when stripping and plucking. Since the outer harsh coat collects the dirt and debris, they usually doesn't get into the pores to cause bacteria. Dirt and debris either comes off with the hair, or doesn't get past the undercoat. If the coat is exceptionally greasy you may wash the coat first, but ideally you would wait three or four days before stripping to allow oils in the coat to build back up. If it is a situation of a non-showing client dog, where that isn't possible, you would still preferrably strip the dirty coat and then bathe. If you must wash the dog first due to excessive grease or grime (not a normal situation), I prefer using a super fine chalk for stripping, like CC White Ice or Iv St. Bernard Jeunesse.