Crimtane Brick

This is how you build in red and black without the biome creeping out of your walls. Turning the stone into brick kills the spread, so you can face an entire base in it and nothing next door will convert. That is the whole reason to use it instead of the raw block, and it is why it turns up in so many arena builds near the evil biome.

A stash of it appears once the Wall of Flesh has died in a crimson world, and since that boss can be summoned again as often as you like, the material never truly runs out. For a large build it is faster to refight the wall a few times than to strip ore veins by hand. The one thing to remember is that it does not hold up to explosives, so it is a poor choice for anything you want standing after a bomb goes off nearby.