Thanks! The shard is pate de verre, ground leaded glass and finely ground (by me:)) glass enamel colorants, based on an old Minoan vase. It's attached to a PMC back plate made with a polymer plate impressing Minoan letters. Fun stuff.
"Hourly Paid Tutor Jewellery
Reference: 102/18/JBSalary: £32.28 per hourHours: 3 to 6 per week term timeClosing date: 3 Sep 2018https://www.morleycollege.ac.uk/about/jobs/1757-hourly-paid-tutor-jewellery"