what is cromalin plate?
(a) Printing
It was originally a photographic process. They now have a digital version -- basically a colour-calibrated high-res inkjet print.
You would laminate a substraight for each color magenta,cyan,yellow and black. Each layer would be exposed to UV through a positive piece of film. The layer remained sticky where it was not cured by the UV and toner was sprinkled over the surface and would stick. You would do this 4 times to give you a very accurate representation of what your piece would look like on press.
Swan Brand teapots were made in Birmingham, England, throughout the middle of the 20th century. It was brand owned by an electric kettle manufacturer by the name of Bulpitt & Sons Ltd and they registered the Swan Brand name in the early 1900s.
Bulpitt made their name and fortune manufacturing the first commercial electric kettle with a submersible heating element.
They began making these Swan teapots in the 1930s and continued in production (except during World War II) until the early 1970s. However, most of them date to the 1950s or 1960s which is most likely the age of yours. They were made from an aluminum or zinc alloy and chrome plated to make them shiny, a finish that the company trade-marked as "Cromalin Plate".