I've explained the process several times. It should be in the archives.

Here is a different approach. Below is a scan of an old badge produced by Whitehead & Hoag. The litho is printed on paper and covered by a film of celluloid. This is the exact same formula used to make the oldest of c&s (pre 1911). After 1910 the paper was replaced with celluloid (celluloid covered celluloid).

The orginal process produced beautiful lithos but they lifted. The celluloid/celluloid inlay remained flat. USPC made c&s to the mid 1940s when Burt took over.