Sugar refining was the basis of Glasgow's Confectionery industry, which continued to expand after the last refinery closed & cheap continental sugar became available. Wotherspoon, Buchanan, Hay, Birrell's, Stewart & Young & Montgomery's, big firms who probably also made chocolate? There were two chocolate factories, Carson's Ltd in Barrowfield & The Sweetmeat Automatic Delivery Company which made chocolate bars for vending machines.
Anent the Coop at Shieldhall, the UCBS main bakeries was in Ballater Street & MacNeil Street & the giant bakeries in Cranstounhill & Plantation of J & B Stevenson plus many others.
Looks like a needle in a haystack situation? Wilton, I think you've as much chance of discovering this as you have in finding the knife used to cut your grannie's umbilical.
