To evaluate the seal seam, dye is applied to one side of the seal. It is then visually examined whether the dye penetrates through the seal. Each side of the sample seal is observed for 5 seconds. The package must not contain liquids or condensation, as this could distort the test results. The dye used must provide strong contrast with the opaque packaging material. One of three methods is selected for seal testing.

Method A: Injection method
The dye solution is injected into the package. The seal is observed to detect possible seal defects indicated by dye leaking from the inside to the outside.

Method B: Edge immersion method
An outer edge of the seal is immersed in the dye solution. If dye penetrates from the outside to the inside, leakage points are present in the seal.

Method C: Pipette method
For this method, one outer edge of the package must remain unsealed. Using a pipette, drops of dye solution are applied to the inner side of the intact seal seam. The seal is then inspected for dye penetration.