COCHINEAL
Is an acid-base indicator made from the bodies of dried female cochineal insects, found in
Mexico and Central America. You'll have to grind about 70,000 insects to make one pound
of dry indicator. The powder is about 10% carminic acid, which is yellow in acidic solution
and deep violet in alkaline solution. Cochineal solutions are not used much as acid/base
indicators these days.
CURCUMIN OR TURMERIC YELLOW
Is a natural dye found in curry powder. It turns from yellow at pH 7.4 to red at pH 8.6.
ESCULIN
Is a fluorescent dye that can be extracted from the leaves and bark of the horse chestnut tree.
You'll need to shine a black (ultraviolet) light on the indicator to get the full effect. Esculin
changes from colorless at pH 1.5 to fluorescent blue at pH 2.