Help! There is a name for the process most used in Japanese sake cups where

[Paper Roses]

a picture is seen in the base when the cup is held to the light. A friend just bought a porcelain tea service with tea cups and a small porcelain pot where these picture show in the base of the cups. She asked me what it is called and I cannot remember. Anyone know?
Thanks

[brer cat]

1. lithophane

They are usually of a geisha. The nudes are quite valuable.

[Paper Roses]

2. That's it! Thank you.

My friend will be happy to know and I'm glad to be reminded.
The tea cups in this set all have the head and shoulders of a geisha within the base.

[grasswire]

3. I learn something new every day!

Cool.