Which of the following are the two general liquid penetrant techniques?

The two general liquid penetrant techniques are color contrast and fluorescent. These methods are utilized in non-destructive testing (NDT) to detect surface-breaking defects in non-porous materials.

The color contrast technique uses visible dyes to highlight defects against the surface of the material. The penetrant is applied, allowed to dwell, and then excess penetrant is removed before a developer is applied, drawing out any penetrant trapped in surface flaws and making them visible as colored indications.

The fluorescent technique also involves applying a penetrant, but this method uses a dye that fluoresces under ultraviolet (UV) light. This can enhance the visibility of the indications significantly, making them easier to detect in low-light conditions. The use of UV light allows for greater sensitivity, detecting smaller defects that may not be as easily seen with standard lighting.

The other options listed involve different NDT methods or techniques that do not fall under the liquid penetrant testing category, thus confirming that color contrast and fluorescent are indeed the applicable techniques in this context.