Complex sentence: Steel of this quality must be made in a crucible and requires much higher temperatures than European blacksmiths of the time were capable of producing at their forges; there is no evidence that Europeans could make crucible steel themselves until the Industrial Revolution 800 years later.
Split into simpler sentences: Steel of this quality required production in crucibles at much higher furnace temperatures than European blacksmiths of the time were capable of producing at their forges. There was no evidence that Europeans could make crucible steel themselves until the Industrial Revolution 800 years later.