Slag is the byproduct of IndustrialCraft 2's Blast Furnace when smelting Steel. Each Blast Furnace cycle in IC2 Experimental consumes 6 Iron Ingots, 1 Coal Dust (or compressed equivalent) and Air Cells, then outputs Steel Ingots together with Slag as a secondary product. Slag is a recycling-economy material: it represents the leftover impurities that the Blast Furnace separates from refined Steel. The item uses a grey-brown crushed texture and stacks up to 64 in the inventory. Slag is not placeable — it is an item, kept in chests, Drums or sorting pipes next to your steel line. In IC2 setups, players macerate Slag for trace dust returns in some configurations, use it as filler in addon recipes, or simply store it as a record of how much Steel a base has produced. Because Slag scales 1:1 with Steel production, it is a reliable indicator that the Blast Furnace pipeline (Iron Furnace heat source, iron supply, coal dust feed, Air Cell input) is running stable. Keep Slag separated from Steel Ingots in the output buffer of your Blast Furnace to avoid mixing it into automated Steel crafting recipes.