How to add dirt and grime to any characters hair

Toobis

I mean any type of hair for any generation Iray/normal/dforce what is the general process here please? What can you use?

onix

Iray decals can work somewhat but generally, you need totally different hair model if your original hair is too fluffy. there are some products where dry and wet hair is provided.

I rather just try to avoid hair getting  wet or dirty if your hair is dark then dirt is not that visible anyway