This technique is suitable for locating pinholes through a non-conductive coating and a conductive substrate.

A sponge, moistened with a wetting agent, is supplied with a low voltage. Normal tap water can be used to moisten the sponge as it contains salts that keep its electrical conductivity relatively high.

To further encourage moisture to pass through the pinhole by reducing the surface tension of the water, a surfactant such as Kodak Photo-Flo™ can be used, Part Number T27018024.

When the sponge is moved over a pinhole, liquid penetrates the flaw and flows to the substrate and completes the electrical circuit.

The resulting current flow generates an audible and visual alarm in the detector.