Windows
Business Glass Block
Glass is a wonderful invention that lets light in while keeping the cold wind out.
Crafting
Craft at Forge · makes 1
Crafted as 
Glass Block: pick this one of its variants when you place it.
- Glass (forge units)× 12
- Lead (forge units)× 5
- Clay (forge units)× 5
Drops when destroyed
Broken Glass× 1-3