I did a bit of research on the biochemistry of cannabinoid production. The best books for this is marijuana botany by R.C Clarke.
There has been some great research that accurately details the chemical transitions during cannabinoid synthesis. The process from clear to cloudy and cloudy to amber is not quite as clear cut as its typically thought. When the resin glands that develop on the flowers of cannabis are clear, this indicates active cannabinoid biosynthesis. When the color starts to become opaque, cannabinoid synthesis is slowing and has passed its peak levels of THC. Which is kind of interesting because many attempt to harvest at peak THC, but harvesting when clear is thought to be quite early for many. Which suggests quite strongly that High THC numbers is not the defining factor in a superior euphoric response. And that other cannabinoids such as CBD and CBN likely play a major part in this.
When color starts to shift amber, this is not a direct result of the degradation of THC to CBN. But research has shown that the timing of this shift indicates very accurately the degradation process. Which is caused by the oxidative process of THC to CBN. However what makes things much more complex in the interpretation of the resin glands is that even when they start to turn amber, this does not mean that cannabinoid biosynthesis is still not developing further, and can be that more time can allow extensive increases in cannabinoid levels, even though THC is degrading to CBN. For example. Amber bulbs that are still transluscent and clear, can be still undergoing cannabinoid biosynthesis faster than THC is being degraded to CBN. However amber bulbs that are opaque are likely degrading and would be wise to harvest at this point.
As far as CBD levels, this is determined mostly by genetics and is hardely influenced by much. However you can use the above information to determine how to obtain a different THC to CBD ratio. As when trichomes start to become opaque, it is generally THC which slows rather than CBD. So letting them develop longer past this peak THC point, will allow CBD to continue biosynthesis and potentially be higher. Though this is very minimal increases and it largely influences the THC to CBD ratio as the degradation of THC shifts faster than the synthesis of CBD.
This is on the list of mine to complete a article which details this process for readers to be able to use to interpret their products more accurately and determine what they actually are after as far as the end result of the product.
