As Kobranek said, it's very important to heat everything up while adding the vinegar and salt.
You need to add enough vinegar so that (most) everything dissolves. Once everything is dissolved then add the salt. It doesn't hurt to filter the solution again before adding the salt just to get a cleaner product in the end.
After you add the salt, let everything cool off slowly. As it cools, crystals should start appearing.
Good luck!
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