However, most grinding balls are solid and do not contain liquid, which makes the leaking black substance unusual.
2. Hollow Float or Buoy Component
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Another possibility is that the ball is part of a floating or buoyancy system.
Large hollow steel spheres are sometimes used in:
Marine equipment
Pipelines
Floating docks
If damaged or corroded, they may develop holes and fill with water or other substances.
Why it fits:
Boreholes could be corrosion points
Internal cavity could hold liquid
Steel construction is common
The black liquid could be contaminated water, oil residue, or decomposed material trapped inside over time.
3. Old Industrial Tank or Pressure Vessel Component
In some cases, spherical steel objects are used in pressure systems or tanks.
These may include:
Gas storage systems
Pressure vessels
Mechanical equipment parts
If such an object was discarded or lost, it might end up in a creek due to flooding or improper disposal.
Why it fits:
Hollow construction
Possible internal residue
Industrial-grade material
The leaking substance could be leftover oil, tar-like material, or degraded contents.
4. Military or Historical Object
Although less likely, the possibility of a military origin cannot be ignored.
Some older military devices used spherical metal casings, including:
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