When specifying glass in a design there are a number of issues to consider:
Glass vs. plastic - (e.g. for packaging, which is better - glass is heavier but more easily recycled, might be kept for longer, prestige packaging?) More information
Glass is 100% recyclable with no loss of clarity or purity. Some regular green drinks bottles contain 93% recycled content.
Clean sorted glass can be easily recycled.  Mixed glass, and dirty glass contaminated by silicone, glue, screen printing and coatings with silver or aluminium make recycling more difficult.  Screen-printed and reflecting glass can not be recycled into first class glass, but down-cycled.
Use your label to remind people to recycle their glass - show them how and where to recycle, do not use a bin symbol.  If you use blue glass - let customers know to put it in the green bottle bank
Interesting links:
- Independent designers network - www.indes.net
- Rediscovering glass packaging - www.devicelink.com/pmpn/archive/98/09/001.html
- Glass Packaging Institute - www.gpi.org/