What roller placement technique produces a full-volume curl by sitting directly on the base?

The technique that produces a full-volume curl by sitting directly on the base is known as on-base placement. When the roller is positioned directly on the base of the hair strand, it allows for maximum lift and volume. This is because the roller's weight and the hair's natural fall are working together to create a curl that has the highest level of elevation from the scalp.

When utilizing this technique, the roller is placed at a 45-degree angle to the section of hair, which not only secures it firmly at the scalp but also encourages the hair to wrap around the roller completely. The direct contact with the base enhances the curl’s bounce and allows for a more defined, voluminous look, making it an ideal choice for styles that require significant height.

In contrast, other roller placement techniques such as half-off base, off-base, and under-base do not achieve the same level of volume or curl definition since they don't maintain the roller at the scalp level. Each of those methods results in a different degree of lift, which is less than what is achieved with the on-base technique.