The heat basically sped up the oxidization process of the tattoo by opening up the skin pores to let in more oxygen, thus darkening the tattoo. However, this heat was in excess. His skin under the tattoo began to swollen and scab. He was in pain for 3 days from the scarring of the tattoo, and it left a semi-permanent scar on his skin for several weeks, then it disappeared completely.
In summary of this experiment, it is not wise to apply extreme heat in any form to a fresh applied Jagua tattoo or painful reaction will occur to the skin.