You may be right Frank: it just appears more recent than 1915.
Gilt was applied to Chance items from 1950, but this was hand applied using a brush. The earliest Chance item with gilt applied was 1960 (Golden Lagoon), but none of the Royal crests used gilt for the 1953 Coronation.
I do have a Johnson Matthey advert somewhere advertising gilt, but haven't tracked it down so far. Not conclusive as it may have been developed much earlier.