It can be a pain to add the nic when you're mixing small bottles of
juice. Having to add a tiny quantity of nic each time when you're trying out flavors and mixing really small bottles of different recipes. Especially when the nic is very strong and you have to be extra careful.
The way a lot of folks do it is to make some diluted base before you start. I get 100mg nic, then mix a few hundred mls at a time of 8mg base, just nic, VG, and PG. If you use 12mg
juice then you could mix base at 15mg or 20mg. It's a lot easier to add a larger quantity of base than a small quantity of high concentration nic. And you only have to handle the strong nic once in a while. If you spill 20mg base on your hand you don't have to worry, just wipe it off with a paper towel.
Once you get the hang of it you can mix your base just a little stronger than where you want the
juice to end up. Like mix 14mg base and rely on the flavoring to cut it down to 12mg. Makes mixing a doddle.
I picked up that tip here soon after I started mixing.