The talc is a little erratic This method works well with flat or nearly flat surfaces.
1. Take the item outdoors.
2. Face away from the sun(to lessen reflections)
3. Take the photo from a fairly low angle - this will make the base appear lighter(as it reflects the sky) and the siganture will be darker because it does not reflect. Here is an example which shows what I mean. Remember sharp focus is all as out of focus can't be readily fixed , if at all.
Ross