In general, the more vinegar the better. It sets the color and makes it brighter.
Well that depends on how much salt and how much water you have
Vinegar is actually mostly water. It generally does not contain any salt.
it depends where the salt water is coming from
The concentration would be about the same as for sea water.
Seawater has a salinity of arround 3.5 percent. So, 1 liter or 1000 milliliters or 1000 cubic centimetrs freshwater needs 35 grams of salt to make "seawater".
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