I recently just got into using a straight razor. One of the items I understood needing was a strop. The sales person at AoS said I needed strop paste, which I see is recommended using. However, everytime I've used it it has left a black film on my strop. At first I thought it was something on the razor that caused it, but I've made sure the blade is clean, and it still keeps happening. The people at AoS said I can clean it off with a rag and warm water. Has anyone had this issue?