Short answers, pulled from the story.
Glass production in Venice began as early as 450 when glassmakers from Aquileia fled to the islands to escape barbarian invaders. The earliest archaeological evidence of a glass factory in the area comes from the Venetian lagoon island of Torcello and dates from the seventh or eighth century.
A law dated the 8th of November 1291 confined most of Venice's glassmaking industry to the island of Murano because furnaces often caught fire and posed a threat to the wooden structures of the city. This decree removed the possibility of a major fire disaster for the rest of Venice while keeping the technology and glassmakers themselves confined to Murano.
Cristallo is a soda glass created during the 15th century by Murano's Angelo Barovier. Manganese dioxide served as a key ingredient in the secret formula used to make cristallo which became Europe's clearest glass at the time.
Napoleon conquered Venice during May 1797 and the Venetian Republic came to an end causing hard times for glassmaking in Murano. Some of the Murano methods became lost under French and Austrian control where tariffs and taxes made glassmaking unprofitable until Venice became part of Italy in 1866.
Foreign imitations and difficulty attracting young workers caused the number of professional glassmakers in Murano to decrease from about 6,000 in 1990 to fewer than 1,000 by 2012. By 2012 about 50 companies were using the Artistic Glass Murano trademark of origin to certify products made on Murano.