Board Thread:Theories and Speculation/@comment-36019309-20190114073523/@comment-32685487-20190211194250

Amaterasu burns as fast or as slow as the caster wants it to. For example, it burned instantly through the fire breathing toads stomach, showing that Itachi was able to make it INSTANTLY go at full temperature and against Sasuke he made it burn fast slower than that but still not so slow as it burned Sasuke's snake shed skin clone half to ashes before Itachi stopped it. Albeit it seems Sasuke can add shape manipulation to Amaterasu but Itachi can control the temperature output on the tech, controlling the rate it burns.