In general, emptiness depends on an object or a particular phenomenon. If the object is transient or adventitious, then its emptiness, although it is not conditioned, will cease to be when the object ceases to be. To put it another way, if the phenomenon ceases, its empty nature also ceases. One reason therefore why we practice deity yoga and visualize the “permanent form” of a deity, is that within our imagination that deity then continues and does not perish. So if take the pure form of the deity as the basis and realize its empty nature, that emptiness will become the svabhavikakaya, the “essential nature body” of a buddha. Otherwise, if we take some impure phenomenon as the basis for realizing emptiness, although the emptiness is the same, the phenomenon does not continue until buddhahood so neither will its emptiness. This is why we talk about emptiness in terms of pure phenomena; in summary, the whole basis for meditation on emptiness is the mind.
His Holiness the Dalai Lama “Mind in Comfort and Ease: The Vision of Enlightenment in the Great Perfection”