Cocaine is super water soluble and it's solutions are water clear. Good coca dissapears in very few seconds when in contact with water; whatever stuff that needs you to be stirring and stirring it in the spoon isn't good gear. If it changes the colour of the solution from water clear to a milky tone, or yellowish or whatever isn't good gear. And, of course, if it left behind "paste" or other kind of residue, that isn't for sure good cocaine.
Btw, boiling down that residue to be able to shoot it to figure out wtf is it, is a real bad idea and worse behaviour, , please don't do it again
Only a thing: I'm very far from lecturing you, but IV cocaine allways means bad bussiness.