I am trying to make a lithophane for my grandma. Which lights behind it. Grandpa past away last year and she carries this picture with her around the house all day every day. I am using the makerlab lithophane maker. Because I bought the Bambu lithophane lights. Is there a way to remove the gray spots? Should I be using something else? Should it be black and white? I have no idea what I am doing. I'm not a picture person.