I got my first 'staybright' (forage cap) capbadge in 1962 (JLRRA, Nuneaton). 'Bombs' where still brass, as was belt buckles and beret cap badges. Button on No2 Dress uniform were also Staybright but we still got issued a button-stick!
Staybrite or Anodised Aluminium badges were first issued in the 1950's with the Sussex Yeomanry (TA) having the doubtful distinction of being the first unit to have a Staybrite capbadge with a King's Crown (KC) dating it as pre-1952. I have a KC staybrite cap badge of The Rifle Brigade (The Prince Consort's Own) in my own collection, again dating it as early 1950's.
If anyone has Staybrite versions of the Royal Sussex, East Surreys, Lancashire Fusilers and Somerset Light Infantry regiments that they are willing to sell I would be very interested.
Anodised Aluminium, otherwise known as Staybrite, (alternative spellings Sta-Brite or Staybright) was/is an Electro-plating process resulting in lightweight shiny badges.
Staybrite replaced brass and white metal as the main metal for British Other Ranks military insignia from about 1950 onwards. Given that King George VI died in 1952, it stands to reason that King's Crown Staybrite insignia is quite rare!
However it was not un-commen to still see brass Kings Crown cap badges still in use long after 1952.