Nic base comes in different strengths as well....100mg nic base which is the strongest you can buy pretty much from any vendor for personal use is dangerously strong and must be handled in a well ventilated area with gloves and it's a good idea to wear a mask because it is concentrated enough to poison you from skin contact if you're not careful...it will have a stronger odor to it. If you try and vape nic base that strong it will kill you, if it doesn't kill you it will poison you and you'll regret it...where as like 12 or 24 mg nic base is the same strength is already diluted down to a strength that can be vaped and is much safer to handle but should still be handled like any other eliquid.
Also...the purity of the of nicotine in the base has a lot to do with it light BigNasty said....this is my personal opinion and experience but I've bought nic from four different vendors over the last couple years and it seemed like the higher the quality and more pure/filtered the less the odor and cleaner the flavor after being mixed into liquid...also, if you don't freeze or at least refrigerate nic base and leave it out at room temperature....once you open the bottle it begins to oxidise and change color and the odor will increase....the color change will begin with in a couple weeks in stronger bases and will take much longer to start in less potent bases as there is less nic in the base to react with the oxygen in the air. after about six months of sitting at room temperature and oxidising the nic will loose about 1-3 percent of it's potentness. Ideally you want to store nic base you plan to use with in six months to a year in the frig and let it sit out to warm up for awhile before use...if you're planning to buy in bulk to save money and store it you'll want to get some brown glass jars and freeze it...nic can last years without oxidising or coloring and staying fresh in the freezer...I have some nic I need to transfer from the frig to the freezer myself soon as I keep putting off my DIY projects and never seem to use as much as I think I will....also, PG and VG bases are good for about a year kept at room temp....they may last longer but I've never kept a bottle around long enough to find out
