In order to produce glass, your map must have sand (or rock crystal, for high-value crystal glass - see below). Sand is never carried by a caravan nor offered by a liaison. This is a dealbreaker*. If you want a glass industry, check on your pre-embark map for sand layers.
- (* Although there is an easy cheat to work around it, if you just have to have glass on an otherwise sandless map.)
To produce glass, sand must first be gathered in bags using a task available at any glass furnace, "Gather Sand". You must designate a Sand Collection zone from the (i)-menu that includes an accessible area of sand in order for this task to succeed. Gathering sand requires item hauling, whilst moving sand bags to stockpiles requires furniture hauling*.
You will need spare bags in order to collect sand, and probably many of them, perhaps a half dozen or more per active furnace. It's also a good idea to build spare furnaces just to have "Gather Sand" orders on Repeat (perhaps 2-4/active furnace, depending on your haulers, rate of glass production and the distance) so as to keep your production furnaces available to accept other tasks. (This is important also to prevent clutter, as the empty bags tend to stack up in the glass furnaces.) These furnaces don't use fuel and are not manned (dwarfed?) for the Gather Sand task, so if you are using magma Glass Furnaces, these can be standard versions, and in an out-of-the-way corner of the map - the sand haulers will never go there, but the orders have to come from there.*
- (* You can also queue up "Gather Sand" tasks through your manager, but some will get apportioned to the active furnaces, interfering with the actual manufacture of glass items. It's better to do this one workshop by workshop.)
Once you have one bag of sand you can order glass to be created at the furnace. A standard glass furnace will consume one unit of fuel per job; a magma glass furnace uses no fuel.
- To produce green glass, you only need a bag of sand.
- To produce clear glass, you also need one bar of pearlash.
- To produce crystal glass, you don't need sand, but you do need pearlash and rock crystals, a gem which is not found on all maps.
Once you have the ingredients, you have two basic choices when making any type of glass - produce raw glass, or produce a specific glass item. Raw glass is treated as a low-value gem, not a raw material - it does not ever get re-melted or processed again into other items, but is further processed by a gem cutter. If you want a glass item, order it specifically from the furnace menu.
See also "Glass" for a full discussion of the properties of glass items.
Glass Industry Flowchart