Prerequisites: Alchemist 6.
When you create an extract or mutagen that provides invisibility, if the invisibility effect would be ended prior to its normal duration, such as by being dispelled or being broken due to you making an attack, the invisibility effect lingers for a number of additional rounds equal to your Intelligence modifier. If something else occurs during this time which would end the invisibility effect, it is ended immediately. In addition, the DC to dispel an extract that provides invisibility is increased by an amount equal to your Intelligence modifier.
On the Inverse Calculus of Unseen Refraction © 2012, Legendary Games; Author Jason Nelson.