How to determine if a paint can is clean?

1. Visual Inspection (Basic Standard): Visually inspect the inner wall of the can, the gaps in the lid, and the threaded joints. A completely clean paint can has a smooth inner wall, with no visible paint clumps, residual paint stains, or sticky residue. Only a very faint trace of the original primer is allowed. If there is a noticeable layer of colored paint or clumps of residual paint, it indicates that the paint has not been cleaned properly.

2. White Cloth Wiping (Precise Verification): Take a clean white cotton cloth or tissue paper and repeatedly wipe the inner wall and hard-to-reach areas. If no visible stains or pigment residue remain on the cloth after wiping, and only a very faint trace of the original primer remains, it is considered clean. If there are obvious traces of paint or oil, it indicates that there are still residues and further cleaning is needed.

3. Odor-Based Confirmation: After opening the lid, smell the inside of the can closely. A completely clean paint can has only a slight smell of the can material itself, without any obvious pungent odor of paint or solvents. If a pungent odor can still be smelled, it indicates that residues have not been completely removed and it does not meet recycling requirements.