Indicator Chart

Part of Acids and Alkalis

A comprehensive reference for natural and improvised pH indicators — how to prepare them, read them, and use them to control chemical processes.

Why This Matters

Knowing whether a solution is acid, neutral, or basic is one of the most fundamental measurements in chemistry. It affects soap quality, tanning efficiency, fermentation health, soil fertility, water safety, and dozens of industrial processes. Without the ability to measure acidity, a chemist is working blind — mixing reactants and hoping.

Modern pH paper and electronic meters are not available to a rebuilding civilization. However, humans have had reliable indicator chemistry available for millennia — it just comes from plants. Dozens of common plants produce pigments that change color predictably across the pH range. Once you know which plants in your region work and how to prepare the indicators, you have a functional pH measurement system that costs nothing and can be reproduced by anyone.

This article is a reference guide. Consult it when selecting indicators for new applications, when evaluating plants in an unfamiliar region, and when teaching others the skill.

How Plant Indicators Work

The chemical class responsible is anthocyanins — water-soluble pigments that change structure (and therefore color) in response to pH. They are found in red, purple, and blue-colored plant tissues: flowers, berries, leaves, and stems.

The color change is predictable: anthocyanins are red in acidic conditions, purple in neutral, and blue-green to yellow in alkaline conditions. Different plants have different specific color-pH relationships, but the general pattern is universal.

Other indicator classes:

• Flavonoids (yellow pigments) — some are pH sensitive in the alkaline range
• Betalains (beet pigments) — shift from pink-red to yellow-orange in strong base
• Curcuminoids (turmeric) — yellow in acid/neutral, red in strong base

Preparation Methods

Liquid Indicator (Quick Method)

1. Collect the indicator plant material — leaves, petals, or berries
2. Crush or chop finely
3. Simmer in a small amount of water for 10–15 minutes
4. Strain through cloth
5. Allow to cool
6. Store in a sealed glass or ceramic container, away from light

The resulting colored liquid can be added drop by drop to any solution to be tested. The color of the indicator changes immediately.

Indicator Paper (Preferred for routine testing)

1. Prepare the liquid extract as above, making it as concentrated as possible
2. Cut strips of porous cloth or paper (handmade paper, cotton cloth)
3. Soak the strips in the indicator solution for several minutes
4. Hang or lay flat to dry, away from direct sunlight
5. Once fully dry, store in a sealed container away from moisture and light
6. To use: touch a moistened strip to the solution being tested, or dip briefly

Indicator paper stores for months if kept dry and dark. Make large batches when the plant material is in season.

Gel/Paste Indicator

For surfaces (soil testing, testing mineral deposits) where liquid cannot pool:

1. Mix indicator extract with a small amount of starch paste or agar (from seaweed)
2. Apply to a test strip or spread on a clean surface
3. Touch the gel to the material being tested and observe color change

Master Indicator Reference Chart

Red Cabbage (Brassica oleracea) — BEST ALL-AROUND INDICATOR

Availability: Widely cultivated; temperate climates Preparation: Chop outer leaves, simmer 20 min in minimum water, strain Color range:

pH	Color
1–2	Bright red
3–4	Red-pink
5–6	Purple-pink
7	Purple
8–9	Blue-purple
10–11	Blue-green
12–14	Yellow-green

Notes: Widest useful range of any common indicator. Distinguishes well across entire pH scale. Deteriorates over 2–3 weeks — make fresh batches.

Turmeric (Curcuma longa) — BEST FOR STRONG BASE DETECTION

Availability: Tropical and subtropical; can be dried and stored for years Preparation: Dissolve dried turmeric powder in a small amount of alcohol or concentrated vinegar, then dilute with water Color range:

pH	Color
1–7	Yellow
7.5–9	Orange-yellow
9–14	Red-brown to brown

Notes: Poor for acid range (no color change). Excellent for detecting strong alkalis — turmeric paper turns brown-red in lye immediately. Traditional test for caustic soda quality.

Blackberries / Elderberries (Rubus / Sambucus) — GOOD FOR FIELD USE

Availability: Wild throughout temperate zones Preparation: Crush fresh berries, strain juice; or simmer dried berries Color range:

pH	Color
1–4	Red-pink
5–7	Purple
8–10	Blue-green
11–14	Yellow-green

Notes: Berry juice deteriorates quickly (ferments or molds). Best made into indicator paper for storage. Good resolution in acidic range.

Red Roses / Dark Hibiscus Petals — DELICATE ACID RANGE

Availability: Cultivated widely Preparation: Simmer petals briefly in water; extract turns vivid red-pink Color range:

pH	Color
1–5	Pink-red
6–7	Mauve
8–11	Green-blue
12+	Yellow

Notes: Very sensitive in the 4–8 range — useful for food and fermentation testing where subtle changes matter.

Beet Root (Beta vulgaris) — ALKALI DETECTION

Availability: Widely cultivated root vegetable Preparation: Boil chopped beet in water, strain concentrated red juice Color range:

pH	Color
1–8	Pink-red
9–11	Yellow-orange
12+	Orange-yellow

Notes: Not sensitive in acid range (little color change below pH 9). Good for quickly confirming whether a solution has reached alkaline levels. The betalain pigment reacts differently from anthocyanins.

Grape Skins / Red Wine — FERMENTATION MONITORING

Availability: Wherever grapes are grown Preparation: Use the grape marc (crushed skins) from winemaking; extract in water Color range: Similar to blackberries — pink in acid, purple neutral, greenish in base

Notes: Best used as a bulk indicator for fermentation monitoring — add directly to small samples of your fermentation to quickly check pH direction.

Field Testing Quickguide

When in the field without prepared indicators, these plants can be used fresh:

Plant	How to Use
Red cabbage	Crush a leaf and rub on test surface; interpret color
Turmeric root	Rub fresh root on paper, touch to solution
Blackberries	Crush berries directly onto test surface
Red petunias	Crush petal onto test paper
Purple morning glory	Crush petal; juice turns pink in acid, green in base

Interpreting Results: Decision Table

Use this table to make practical decisions from indicator color readings:

Result	Red Cabbage Color	Action Needed
Strongly acidic (pH <4)	Bright red	Dilute or add lime/ash to neutralize
Mildly acidic (pH 4–6)	Red-purple	Acceptable for vinegar, fermentation, mild acid work
Neutral (pH 6–8)	Purple	Correct for drinking water, most food production
Mildly alkaline (pH 8–10)	Blue-green	Acceptable for soapmaking (mild), some tanning
Strongly alkaline (pH >10)	Yellow-green	Correct for lye soapmaking; dangerous to skin

Calibration and Comparison

To build confidence in your indicator system, prepare solutions of known pH to calibrate against:

• pH ~4: Dilute vinegar (1 part vinegar, 4 parts water)
• pH ~7: Fresh rainwater or distilled water
• pH ~9–10: Dilute baking soda solution (1 tsp in 1 cup water)
• pH ~12–13: Dilute wood ash lye (weak solution)

Compare your indicator’s response to these standards to understand its color range before using it on unknown solutions.

Preserving Indicators for Long-Term Use

• Store liquid extracts in sealed, dark-colored containers (light degrades anthocyanins)
• Add a few drops of vinegar to liquid extracts to inhibit mold growth (does not significantly affect the indicator’s function since you account for the slight acidification)
• Dried indicator paper lasts 3–6 months if sealed from moisture
• Fresh plant material can be dried and ground — reconstitute in alcohol or water as needed

A well-stocked indicator kit — red cabbage extract paper, turmeric paper, and blackberry extract — covers the full pH range from 1 to 14 with enough sensitivity for all practical chemical work. This $0 investment in plant chemistry is the foundation of all other chemical measurement.