This topic has got me thinking about something related and possible off-topic but...
What about when Harry redirected the malocchio (the frozen turkey)
?
He improved it so I assume it was an evocation. A block would have protected the target but wouldn't redirect the spell. It's more like a counterspell used to catch the spell's energy, instead of countering it, and then recasting the original spell. An evocation using another spell as the energy source instead of gathering power yourself? And you would not need to have any knowledge of the "element" use for the original spell.
Just a random thought to toss in: what about single/limited use items to "block" spells, as seen in the short story "The Warrior"; how would those be factored in?
As we saw it, it soaked up Harry's spell and burned out afterward, making it impossible to trace or use again.
Would something like this be considered a potion (and would you consider one-shot talismans like this as potions?), or as an enchanted item?
Just curious now that InvisibleHoser mentioned enchanted items.