I don't think the contaminants is useful information, unless it has combat relevancy. Poisoned weapons would be good info to have and it'll presumably be easier to poison weapons in the future.
The quality differences are very nice to look at and you can still tell the material easily. When the battlefield is littered with copper, iron, bronze, and steel items, it's important to be able to distinguish by the material and I think you have a subtle enough difference in quality that it won't get in the way of that. Contaminants would make that more... busy, I guess?
Poisoned Weapon Attempts. Not skilled at all as a pixel artist at all, just proof of concept.


You can still tell it's steel at a glance. Clear green poison sheen on half. Quality/wear level won't get in the way of that.
I don't know how you solve the problem of quality levels looking visually distinct without adding a visual style that would only really fit for "
Decorated" objects. Quality, Wear, Material, and Contaminant (as long as it matters for combat effectiveness) are important pieces of information that would be nice to not have to fiddle in menus to see. As much as I'd hate to say it, sacrificing a visual look for quality may be for the best. But it'd be cool if there was still a "decorated" and "artifact" sprite even if you can't get a unique sprite for the 6 other levels of quality.