I have made carbon prints with and without relief. Relief takes a much thicker layer of gelatin to remain as relief once the gelatin dries and shrinks.

My first carbon prints had a relief when wet, but completely flattened out when dry. Seeing the wet relief is what led me to experiment and find a way to keep the relief in a dry print. I was successful, but it requires exposing a very thick layer of gelatin in the shadows and a thin layer in the highlights (by reducing the pigment concentration of the gelatin and using negatives with a high density range (2.5 or more). YMMD.