Essence weaves apparently do not backfire very much! They are very safe to make because no essence is actually being manipulated when one is making a weave. Using them can backfire, if one doesn't check their work before using it, or if one doesn't follow the weave's instructions.

And then, because Gren is interested, she explains how essence weaves can be used to make plants that will grow a substance that can be easily refined into whatever material the weave is made of. This is quite terrible for getting the shape of an object correct, but for materials... You can grow infinite amounts, with space and water and sunlight.