It probably won't hurt you, but I wouldn't risk it, just in case. Glazes for food containers are unlikely to contain lead, but may have other metals that are harmful in sufficient quantities. These include cadmium, barium, cobalt, strontium, chromium, and in the case of some older orange ceramic, URANIUM.
Blue glaze is probably copper or cobalt based. I found a reference on ScienceDirect about high blood cobalt levels in association with lead poisoning from glazed Greek earthenware. This indicates that cobalt can indeed be leached out of the glaze and absorbed into the body. Cobalt is eliminated rapidly, but is moderately posionous, and copper is problematic in large quantities. Which brings this back to where I started: it won't kill you, and probably won't make you sick, but it's not really worth the risk.
File it in the same category as eating egg salad left out in the heat a few hours?
One other caution: prolonged contact with acid may damage and discolor your formerly handsome crock, in addition to leaching out these metals. To check for this, you can leave white vinegar in the container for a week or so, checking for change in color of the vinegar and the container every day.
My accidental vinegar just happened, and I have been able to propagate it by pouring the last few teaspoons from one bottle into the next (after drinking half of the next bottle).
It goes pretty slow using an open bottle (too little circulation) but it does go. I open the bottle every day or so and swish the contents around. It takes about 1 weak to even start smelling vinegary, and circa one month to really develop.
I've been sticking with the same variety of wine and not trying to diddle the sugar content.
I still have not developed a mat-like mother, but there does seem to be a culture there. I'm on the fourth generation now.
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I think it makes no difference as the vinegar does not contain bacterial spores. If so much vinegar that makes the soup significantly more sour then it can eventually go wrong even later as bacteria don't prefer the acidic environment.
To add a concrete quantitative example: while cooking 3 pieces of beetroots I added 5 tsp 6% acetic acid balsamic vinegar. 7 days later kept in fridge (~4C) is still good. I am quite sure it's because the acidity as meals used to go wrong much sooner than 7 days.