"I used a glass lid from another Weck jar, and covered it with 2 layers of cheesecloth."
Ferments need to be in an oxygen-free environment. Cheesecloth allows mold spores in. That black stuff looks like mold. As it's a small jar, I'd pitch it. Too much risk.
I don't think the evaporated brine is the issue, I think it would of gotten moldy on top of the brine even if it still covered the vegetable/cabbage. Hopefully others will chime in.
There was a post by Chili Monsta (it might have gotten stickied) about yeast, molds, saving and such. I'll see if I can link it~
edit- it is pinned in this Making Hot Sauce section.
Thank you for the insight. I'll take a look at the Hot Sauce section.
Looking over my original post, I see I may need to clarify a point. The cheesecloth was covering the jar, not the lid I was using as a weight.
Not meaning to belabor the point, but how would I create an oxygen-free enviroment, even using an airlock? There's still air trapped inside a bottle when you use an airlock. All the airlock does is allow for expansion without letting more air in, right?
As you say, the cheesecloth allowed mold spores in, but I still can't help but think evaporation played a part in the equation.
I'm hoping you can shed some light on this for me. And, yes, it's been pitched.