Zhenya didn't realise the silver shield wasn't actually silver. She put that piece of information in her brain, hoping it would stick there so she could write it down after class. But what were some down sides of using it over protego? Zhenya thought about it, but it was a bit of a tricky question. What were some negatives? She could probably think of a few small ones, but nothing really obvious. She thought some more, then raised her hand. Any guess was better than no guess. "One possible down side," she thought to herself, not really sure HOW the spell worked, "Could be space? If the user had to cast the spell in a really small space could it not work?" Being that it was a solid shield and all, was the spell conjured in varying sizes? She wasn't sure.