Ashes represent whatever was once alive, whether it be plant, animal, or human life.
I cannot think of any material that encapsulates more emotion then the ashes of a loved one, or in making a picture using the ashes of a loved one. The ash picture could also be a picture of that person’s favorite place, or a picture that makes a statement about their life, or a picture of something that person was passionate about as examples.
Ashes also remind us that life is fleeting
As noted in a common prayer: Man comes from dust and ends in dust; he wins the bread at the risk of his life. He is like the potsherd (Fragment of a baked, clay vessel), that breaks, the grass that withers, the flower that fades, the shadow that passes, the cloud that vanishes, the breeze that blows, the dust that floats, the dream the flies away.