acidic stain

ac·id·ic stain

a dye in which the anion is the colored component of the dye molecule, for example, sodium eosinate (eosin).
References in periodicals archive ?
It also has a high tannin content that results in a blue, acidic stain when the wood comes in contact with metals in wet conditions.
If you want to neutralize an odor or a stain but don't know its pH, try this test then use an alkaline cleaner on acidic stains and an acidic cleaner on alkaline stains.