Medieval secrets and lies

I blithely told Dougie one morning that in medieval times in Murano, glass techniques were kept so secret that some guild members or spies had been killed... his eyes lit up and requested I be more forthcoming...so now i'm trying to find out if I just made it up, read a book of fiction or if there is some truth.......or if I may have to retract my scandalous remark

Murano, Its Glass and Its People
Reprinted by courtesy of both Vetri Murano: A Consortium of Glass Factories in Murano Island and the Venice Chamber of Commerce. Edited by Stanley B. Kruger

Start reading at chapter 2

'Despite the way the glass recipes and the working techniques were kept secret, every innovation soon became common knowledge in the island, thanks to a true network of industrial spying. The wile of Giorgo Ballarin, a poor Dalmatian boy called “ballarin” because of his lameness, is well-known. By pretending to be a simpleton, he was able to watch the preparation of the recipes by great master glassmakers without arousing suspicion. He then wrote them down, learned the glassmaking trade and set up his own business. When he died, he was one of the biggest glassmakers on the whole island, leaving generous bequests and paying for the erection of a magnificent tomb.'

'After the invention of crystal glass, the measures became more severe and it was soon established that only those who had full Murano citizenship could work glass as makers and as apprentices.'

http://www.dvpaperweights.org/newsletters/murano_pt1.html

well that's encouraging but no murderous skullduggery ...yet!

Contemporary fiction: haven't read them
Through a glass darkly / Donna Leon
The Glassblower of Murano / Marina Fiorato


mmmm...though as yet I don't know exactly where this information comes from

'At the time it was rumored that the Maggior Consiglio even hired assassins to capture or kill artisans who left the island.'

http://www.fossilfly.com/history_of_Murano_glass_page2.htm