Color change in e-liquids is a natural process that is affected by a variety of factors. All e-liquids are susceptible to color change, however it affects some liquids more than others.
The major cause of e-liquid color change is oxidation. Oxidation is a natural chemical reaction which occurs as a result of exposure to oxygen in the air. Many e-liquids contain nicotine, which is very reactive. This is especially true when exposed to air, light, or heat, in which case they tend to turn darker. To help prevent this, e-liquids should be stored in dark, cool places. The rate in which oxidation occurs also depends on the type of vaping device being used. Clearomizers, in particular, can increase the speed of oxidation due to the high amounts of heat that they produce.
Another reason for color change in e-liquids is their ingredients. Color change is likely to be observed in e-liquids with a vegetable glycerin (VG) base because they tend to be dense and sweet, meaning that they caramelize when exposed to a lot of heat. This build-up in the coils may cause color change when the tank’s refilled. Color change may also be as a result of the flavor used. Some flavors are more prone to color change than others. You’ll find that sweet flavored e-liquids change color faster than the less sweet e-liquids.
Age also a factor in color change. An older bottle of e-liquid will likely be a different color than a fresh bottle of the same flavor. That doesn’t mean, however, that the liquid has gone off or is no longer vapeable. E-liquids have a pretty long shelf-life if stored properly, so the liquid is still more than likely good to go. It may even be better with the extra steep on it. 😀