I will post but I am far, far, far from expert so hopefully so long term member will reply and give a more measured opinion.

First, when you say "it shows no effect"...what are you doing? Are you vapourising it....what pipe are you using? I wasted my first pulls by not vaping the crystal properly, I was burning it and getting very minor effects. It took me a while. How long after pulling did you vapourise. Did you dry it? Was it stored for any length of time?

I use STB, no washing and find if you get the vape spot on there is very little harshness to the vapour. Hope this helps a bit. Stick with it. Hopefully some expert will also reply.

PS I infer that you freeze precipitated the naptha to get the crystals before washing?