A lash fan is formed by _____.

A lash fan is formed by joining two or more single eyelash extensions at the base while their tips are spread out. This technique allows for a fuller and more voluminous look compared to using just a single extension. The fan creation technique is essential in volume lash applications, where the aim is to enhance the overall appearance of the lashes by providing depth and density.

The structure of the fan is crucial; it allows for a seamless blend with natural lashes, enhancing the eye's appearance without compromising the integrity of the natural lash. This method also helps distribute the weight of the extensions evenly across the natural lashes, improving comfort for the client.

In contrast, using a single lash extension for a fuller appearance wouldn’t create the fanned effect that characterizes volume lashing. Applying multiple lashes to one natural lash doesn't account for the technique of fanning, as it often leads to potential damage to the natural lashes. Lastly, creating a layered effect with different lash lengths pertains to styling rather than the formation of a lash fan specifically. The focus is on the joining technique, making the second option the correct choice.