What are the two types of Penetrant Testing?

The correct choice focuses on Colour Contrast testing, which is one of the key methods used in penetrant testing to detect surface defects. In Colour Contrast testing, a penetrant is applied to the surface of a material and allowed to seep into any cracks or discontinuities. After sufficient penetration time, the excess penetrant is removed, and a developer is applied. The developer draws the penetrant out of the defects, and the contrast in color between the penetrant and the developer helps to highlight the location and extent of any flaws present. This method is particularly effective because the color difference makes it easy to identify defects visually against the background of the surface.

The other options, while related to various testing methods, do not represent the recognized types of penetrant testing. Developer testing is a component of the overall process but not a standalone type. Infrared testing is unrelated to penetrant testing, as it is used for thermal imaging and assessing heat patterns in materials. Viscous penetrant testing would not be a standard term used to categorize the types of penetrant tests. Therefore, Colour Contrast testing stands out as the correct focus for types of penetrant testing in this context.