Which condition is known to affect the rate and extent of liquid penetrant entry into small openings?

The surface condition of the specimen being tested plays a crucial role in how effectively liquid penetrants can enter small openings. A clean, smooth surface allows for better wetting and penetration of the penetrant into cracks and other discrepancies, while a rough or contaminated surface can hinder this process, reducing the effectiveness of the testing method.

The surface condition can influence factors like the presence of contaminants (such as oil, grease, or dirt), which can create barriers that prevent the penetrant from entering cracks effectively. Moreover, surface roughness can affect the wettability and the ability of the liquid to spread across surfaces, further impacting the detection of defects.

In contrast, while temperature can influence the viscosity of the penetrant and the cleaning effectiveness, and the type of penetrant and size of cracks are also important considerations, they do not directly relate to the specific condition of the surface which can significantly enhance or impede the penetrant's ability to enter openings. Thus, the surface condition is fundamental in determining the success of liquid penetrant testing.