Samuël de la Bella was a certified diamond cleaver (klooven). His change in career was likely only due to the German occupation, as Samuël had been a member of the diamond worker's union since shortly after his 18th birthday.
Samuël had paid his dues and updated his contact information last in July 1939, suggesting he was an active diamond cleaver until the Reich invaded the Netherlands. In Reich territory, Jews were forbidden from working with precious stones, including diamonds, hence why Samuël may have had a last-minute, forced career change.