When did plate armour replace chainmail?

It never fully replaced it — the two were worn together for over a century. Rigid plate reinforcements appear from the mid-1200s, and the first near-complete plate ('white') harnesses date to around 1400–1420. Mail continued to guard the gaps at the joints, throat and groin.

How heavy was a full suit of plate armour?

A fifteenth-century field harness weighed roughly 20–25 kg (45–55 lb), distributed over the whole body — comparable to a modern soldier's kit and far lighter than the myth of the 'crane-lifted' knight suggests.

What is 'white armour'?

'White armour' (French harnois blanc) is fully plated armour left bright and polished rather than covered in fabric — the classic look of the fifteenth-century knight.

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The Evolution of Plate Armour (1200–1500): From Mail to the White Harness

How European armour changed from the mail hauberk to the fully articulated plate harness between 1200 and 1500 — the coat of plates, the great bascinet, and the first 'white armour'.