As the name implies, the sandwich dial utilizes a layering technique. It’s unique to Panerai, but the Florentine watch brand did choose laminated dials early in its history to create highly luminous watch faces. According to Panerai, its vintage military replica watches were so glowing that the Italian Navy combat divers who wore them sometimes had to cover the dials with mud to prevent detection. 
Panerai’s sandwich dial consists of two separate discs, with the bottom layer placing the luminous material in recessed indexes and the top layer having index cutouts that allow the bright material to pass through. When looking at copy Panerai’s sandwich dial, you will immediately notice this excellent stencil effect.
It’s worth noting that the earliest examples of Panerai’s sandwich dials used three layers: the highest plate was perforated, the middle plate was transparent Perspex, and the bottom plate was solid and coated with the luminescent paste. However, this was replaced by the two-layer construction we are familiar with today.
Much to the chagrin of Panerai enthusiasts, it seems that Panerai no longer uses the sandwich dial on most of their current replica watches, leaving the technique to specific versions.
In contrast to the sunken indexes of the Panerai sandwich dial, the Panerai sausage dial has painted hour markers that protrude slightly above the dial. In some models, the index is first etched on the dial and then filled with luminous material. In other versions, the luminescence is drawn directly onto a flat surface.
Regardless of the technique used, the result is that the numerals and stick markers are more curved, swelling and curving around the dial, which ultimately provides the way for the (unfortunate) nickname of sausage. If you prefer to use the term (as I do), these are also known as Panerai Painted Dials.
Panerai’s painted dials are not to be confused with Panerai’s printed dials, which have a flat surface. So remember, the next time you browse different Panerai watches to decide which one you like best, take a close look at the dial and see if it is sandwich, sausage (aka painted), or printed. This seemingly small detail can make a big difference in the overall look of a watch.
Put Panerai’s sandwich and sausage dials together, and you’ll immediately notice the difference. Some people prefer the sandwich dial for its style and because it is closer to the dials that came with earlier Panerai fake watches. However, fans of Panerai’s sausage dial say that this design offers better readability from all angles because there is no recess effect. The curvature of the crystal and the indications of the depressions sometimes cause distorted viewing.
Both dial designs offer a unique look, and both have a place in Panerai’s history. I’ve always liked the stencil typography, so I lean toward Panerai’s sandwich dial. However, I have nothing against Panerai’s sausage dials (aside from the dreaded nickname), as they are also quite good-looking.