I offered some Mysterious Embossing Instructions which included a clue you can download and print out.
This video explains the clue I gave, my reason for offering it in this way and a demonstration of how I use indirect light and a three-dimensional view to make quick and effective work of embossing harmonica slots.
With this method, you get benefits similar to using a microscope and a light-table but avoid the respective disadvantages and limitations of those devices.