Thomas trainz faces
These eras are usually defined by repaints and changes in appearance between seasons and are grouped as such. When looking at the run of the model show, there appear to be 4 separate era concerning the faces. A select number of early faces had eyebrows sculpted on, but most simply had the eyebrows painted on. The newly cast face would then be sprayed grey and eyebrows and any other needed details would be painted on. You can see that the eye holes were cast into the face leaving just a thin sphere shaped layer of resin (so thin light can shine through it) over the eye holes on our production made unused cast of Edward's mad face. The faces were sculpted in clay, and these sculpts were used to make the moulds, but anything seen on screen was cast in resin, nothing made of clay ever appeared in the show. It's important to note that despite the common misconception the faces on screen were made of clay, they were actually resin. resin was then poured into the mould to create the faces you see on screen. Once the mould was finished and it came time to cast the actual faces, clear perspex balls (the same one used for the eyeballs on the actual models before they are sprayed white) were placed into the mould to make sure the eye holes would be cast directly into the face and would not have to be drilled out later. The original item (In this case the clay face sculpt) will be taken out of the mould and resin will be poured in to create casts. It is called a 2 part mould because the mould splits in 2 to cover both sides of the object being moulded, meaning the entire object can be moulded, not simply the front or back. Here's a non-Thomas related image of a 2 part mould. Once the face sculpt was complete, it was taken off the Perspex tray and a 2 part rubber mould was made of it. One of James's faces being sculpted on his specified Perspex plate. Each character had a different plate with their own correct eye spacing on which their faces were sculpted. This was so the eye holes would match up to the eyes on the prop. The faces were originally sculpted in clay atop clear Perspex panels with eye shaped half spheres attached to them to act as the character's eyeballs.