hypothetically speaking lets say that a friend want’s to dissolve some of this stuff , what would be the best to do it with? PEG 400 or PG on it’s own? if you use PEG400 do you then add PG/VG to it for a vape ? Assuming you’re making a, I mean your friend is making a C-Liquid, VG/PG will dissolve it fine. If it’s just to store it, whatever you prefer. In the case of C-Liquid I wouldn’t go over 2mg per ml.  1000mg per gram, so 500ml of PG/VG = 2mg per ml ? should he want to use the whole gram for it? or could it be made up into lets say 100 or 200 ml of PG/VG and then that used to add say a few drops to a normal 10ml of vape juice? Maths seems right. It’s best practise to make smaller batches to avoid a downwards spiral of daily use and corresponding mental, social and possibly professional difficulties. Also yes, adding to an inert, normal liquid until you’re, I mean he’s happy is the way to go. But it’s the end product, i.e. the C-Liquid + normal E-Liquid that needs to be a maximum of 2mg/ml. Less strong, however you get there, is better. No one wants a noid overdose, it’s seriously horrible. So warn him to take care.