The original enamel used from the 80's was called Hard enamel as it was baked on and very hard and difficult to damage - they then moved to the cheaper stuff that just popped out all the time and that was called cold enamel as it was just poured onto the helmet plate after it has been chromed and lastly some forces helmet plates have cold enamel and then a plastic cover on top to prevent the cheap enamel popping out.
You can see it on my web page as the plates are listed
Hi, The older type hard enamel is called VITREOUS ENAMEL. This is a coloured glass powder which is then melted in a kiln to produce a hard glossy glass finish. The new softer enamel is called EPOXY a bit like a coloured araldite. This method tends to leave the lettering and detail proud of the colour and often comes away in a single piece. The clear plastic covering often seen on later badges is called CHRYSTAL RESIN.