Here's something I have wondered about for 30 years; what is the sediment that is on the bottom of a quart/liter bottle of oil. It cannot be seen in a black plastic bottle, but in most others it is visible. Seems to be more of it if the oil has been sitting around for a while. I always thought that it was the impurities from the refining process, but now wonder if it could be additives that have come out of solution. Any thoughts?