When Dumbledore and Voldemort duelled, Lord Voldemort countered Dumbledore's attack with a "silver shield". I'm wondering what the exact nature of this shield is. In other words, is the shield a silvery, more powerful, version of Protego, or is it a tangible, physical silver shield?
I think it is indeed a physical object but J.K. Rowling is sometimes ambiguous in her descriptions, so I would very much like to hear your interpretation of canon.
Dumbledore flicked his own wand: the force of the spell that emanated from it was such that Harry, though shielded by his golden guard, felt his hair stand on end as it passed and this time Voldemort was forced to conjure a shining silver shield out of thin air to deflect it. The spell, whatever it was, caused no visible damage to the shield, though a deep, gong-like note reverberated from it - an oddly chilling sound.
Order of the Phoenix, chapter 36