Strange "Phenomenon"

[Geo]

Hi .
Before 5 days i went to detect old buried objects with my LRL. Basically i wanted to find a object who will give me a strong signal so to have it as reference when i make every modification on my LRLs. But no one signal.
After it i went to a farm where there are a lot of old broken buried ceramics.I believed on this "archaiology" place to find a good signal. I found another problem. A lot of signals but not so strong. I received at least 30 different signals, but when my LRL beep 3...4 times then i must waited 0.5 ... 1 minute so to receive the signal again. The time was 21:00 and temperature 23o celsius. So i want your opinion ... was the small signal from the alone small objects deep in the ground or the signal was from ceramics, because more of the old ceramics have iron oxides who metal detectors detect them.