With the release of Arch-tempered Kulve Taroth, a new type of appraisal item has been added to the possible Siege rewards. These items, called Incandescent weapons, have a very high chance to be appraised into regular Rare 8 Kulve Taroth weapons, as well as new, more powerful Rare 8 weapons added with Arch-tempered Kulve Taroth.
The announcement video for Arch-tempered Kulve Taroth mentioned that inciting Kulve Taroth's fury and triggering her new phase during area 4 may be a requirement for receiving these weapons, as well as an all-new "Rainbow" reward slot rarity. It seemed, however, possible to receive Incandescent weapons from gold reward slots as well.
How do all these mechanics tie together? Is Kulve Taroth's fury required in order to obtain Incandescent weapons? How do you maximize the amount of Incandescent weapons obtained from the completion of a Siege?