This brief guide will let you know how to make Glass in Icarus. You have to follow the step-by-step instructions in this guide to do so.
The first thing you need to make glass is Silica Ore; you can find it on the edges of the map, as shown in the image below.
Once you find it, you have to grab it and then go back to your base. You will have to open your tech tree; you need a concrete furnace on tier level three.
You can craft it using concrete mix epoxy rope and an iron ingot. Once you have it, you need to put the silica in the concrete furnace, fuel, and some wood. And then activate the concrete furnace to make the glass.