I was going to start a thread on glass aquariums, but milooo started this one first and I figured my thread would just be rolled into it anyway. So here's my spiel and take it on face value or discount it, you're choice. Besides that's what discussion forums are all about, right?
Glass is made of sand, sand has silica in it, melt it all together at 1200 degrees and you have a nice shiny, clear piece of glass with nearly 3/4's of it containing silica. Not sure how it can't leach it with that content (%).
"The resulting glass contains about 70 to 74% silica by weight and is called a soda-lime glass. Soda-lime glasses account for about 90% of manufactured glass."
Glass - Wikipedia, the free encyclopedia
The only exception I can see is tempered glass has much less, since when we'd custom cut/ and temper smaller pieces in-house, the filtration system on the furnace did have a scrubber that dealt with burn off (silica?) from the glass while it was cooking. But that was a long time ago and can't confirm if silica content is reduced during the annealing process.
Toughened glass - Wikipedia, the free encyclopedia
New tanks leach silica from the surface until it's depleted, which IMO
accounts for the (avg) 2 months of BA in a new tank.
Here's one more piece of info from a website that's one of my goto's on a regular basis.
"Silicates leach from new glass or new sand (glass and sand are silica based). It is not uncommon for new tanks to have algae growth due to silicate leaching."
Read more: How to Reduce Algae in an Aquarium | eHow.com How to Reduce Algae in an Aquarium | eHow.com
I've got more on acrylic tanks and their limitations, but since this thread is about glass, I didn't want to go off topic in order to answer HN1's question.