When I heard that there were paintings inside the Palazzo Vecchio in the center of Florence depicting the Artistic Glassblowing Studios run by the Medici family in the 15th Century, I had to go and see for myself.
There are actually 2 paintings associated with glass in the room called the Studiolo in the Palazzo Vecchio, you need to book a special tour to go and see it. To get to the Studiolo you are escorted through secret passageways inside the castle walls themselves! If you are ever in Florence, I recommend paying a few extra euros for the tour.
The painting above depicts the Medici's Artistic Glassblowing Studio which was located in the Casino Mediceo di San Marco. Notice the glass furnace at the top of the painting.
I also went to the Casino Mediceo di San Marco in the center of Florence, however the building now houses the Court of Appeals in Florence, so access is limited.
Below is the other painting pertaining to glass located in the Studiolo, it depicts the discovery of glass, and if you look closely in the lower right hand section of the painting you can see 2 figures "discovering" glass in the embers of the fire.