These weapons are semi-translucent or opaque green and give off a greenish-glow in the dark. They begin appearing randomly in the world and on opponents after player level 12. Strangely the Glass Longsword does more damage (at max health) than the Glass Claymore. On another note, If you complete Valus Odiil's quest "The Killing Field" and both of his sons survive then you will receive Chillrend (a unique glass shortsword). He is located at the Grey Mare in Chorrol.
"Base Value" refers to the actual value without mercantile or disposition affecting it.
"Max. Damage" refers to the maximum amount of damage an item can do, assuming maximum stats and skill.
"Health" refers to a weapon's durability, "speed" refers to a weapon's attack speed, and "reach" refers to how close an opponent must be in order to be struck with a weapon. Also there are replicas in display cases that look the same but they're weaker than rusty iron.