Is my blue glazed crock safe to make wine vinegar in? I have an urge to purchase a "vinegar mother" and make homemade vinegar with leftover red wine. According to what I have read, it is not a difficult process, and I have had great success with making kombucha, which is a similar technique, only uses tea and sugar rather than wine. I have a lovely dark blue glazed crock with a spigot at the bottom that would work charmingly, if I could verify that it would be safe to use.  Is there any risk of the acid of the vinegar reacting with the glaze? Is there any way to test whether it would or not? 
Thanks, and any advise on vinegar making is appreciated, as well as good sources for buying a mother.
Acid promotes the leaching of lead from pottery glazes.
Of course, not all glazes contain lead.
The FDA claims that hardware-store lead test kits work on pottery:
How can I find out if my ceramicware are safe?