Do I not detect the 18 stamp inside the case back? This would indicate solid 18 karat, not 24 karat. Anyway, nice watch.
Grandad retired from Fry's Chocolate Company in 1924 after 47 years service ..........
Even if it wasn’t marked it’s extremely rare to find anything made from pure gold as it’s quite soft. Maybe 22k is used occasionally, but 18k is definitely the default choice for a top quality “solid gold” case.