Silver plate is a crafting component in The Witcher 3: Wild Hunt. It is not needed to craft anything but can be dismantled into silver ingots.
Crafting Requirements 
It can be found as random loot, in the reward chest for Nilfgaardian Treasure, or purchased from the following merchants:
- All armorers and blacksmiths, except the one at Ardaiso Quarry
- Antiques merchant in Hierarch Square
- Armors and weapons merchants in Nilfgaardian Army Group 'Center' Camp
- Merchant in the boatyard south of Refugees' Camp
- Merchant at Calveit Watchtower
- Merchant at Coast of Wrecks
- Merchant in Ursten
- Merchant by the road west of White Eagle Fort
- Merchant at the sawmill northeast of Rannvaig
- Merchant at the Isolated Hut on Hindarsfjall
- Merchant in Mohrin Village
- Merchant in Stacheier
- Ofieri merchant at Upper Mill
Silver plates can also be obtained by dismantling ornate shields or any of the non-grandmaster Wolven chest armors.