The bluing process is often accelerated and intesified with the use of heat. On a molecular level, heat gets things moving! All things become more pliable and receptive to change when they are heated.  This science can be applied to bluing steel as well.  Warm steel will take bluing faster and often deeper than cold steel.  It's important to note that extreme heat is not necessary, and should not be used unless by a trained metal artisan or blacksmith.  Heating steel with a hair dryer or heat gun is sufficient to get all the desired benefits.  Heated steel should not be so hot that in can't be handled.  If using a heat gun be mindful of non-metallic parts that could be damaged by heat such as wood, plastics and resins.  Never heat Van's Gun Blue.  Heating the bluing itself could create vapor that may be harmful to breathe.  Only heat the steel being blued.