Night (9 - 10pm) On 17th September I was out metal detecting on a field in Essex, As I was metal detecting in a ploughed field, I looked over to the lane next to the field where my car was parked to see the police checking over my car, most probably wondering why a car was parked on its own in the middle of nowhere, at the same time I noticed over the estuary a large airplane heading in my direction above coryton oil refinery, a moments thought was that this was going to pass right over me, instead it swiftly suddenly changed direction to then disappear, I thought well thats strange, on a very clear night, so I decided to watch in the flight path it went to see if could be seen again, then it came out of nowhere again for a couple of seconds then went again for good.I am a little uncertain of things as I was also watching the police at the same time, however, I definitely saw something that did not behave like any airplane, it seemed to be transparent except for lights either side.I often metal detect at night and see many planes, this was not one.This aircraft had the ability to disappear and reappear.