Other Plant Dyes

Part of Acids and Alkalis

A survey of plant-based pH indicators beyond red cabbage, covering turmeric, blackberries, elderberries, and other natural sources.

Why This Matters

Red cabbage is the most famous natural pH indicator, but it is seasonal, requires refrigeration to keep fresh, and may not grow in your region. Understanding a broader range of plant-based indicators gives your community redundancy — if one source fails, another can step in. This knowledge is especially valuable for testing soil acidity, monitoring fermentation vats, verifying lye strength, and identifying unknown substances.

Beyond simple red/blue color shifts, different plants produce indicators sensitive to different ranges of the pH scale. Some are better for detecting strong acids, others excel at spotting alkaline conditions. A community chemist who knows several indicator plants can triangulate more accurately than one who relies on a single source.

Plant indicators have been used for centuries in textile dyeing, where the same plant pigment shifts color in acid versus alkaline mordant baths. That dye knowledge translates directly into chemistry knowledge — the dyer’s art and the chemist’s art share the same root.

Common Indicator Plants and Their Behaviors

Turmeric (Curcuma longa)

Turmeric root or dried powder produces a bright yellow solution in neutral and acidic conditions. In strongly alkaline conditions (pH above 8) it turns red-brown to brick red. This makes it particularly useful for detecting alkalis rather than acids.

Preparation:

1. Grind dried turmeric root to powder or use commercially dried powder.
2. Soak 1 teaspoon of powder in 100 mL of rubbing alcohol or strong grain alcohol for 30 minutes.
3. Filter through cloth or fine sand to remove solids.
4. The golden-yellow liquid is your indicator solution.

Reading results:

Color	pH range
Bright yellow	pH 1–7.5 (acid to neutral)
Orange-yellow	pH 7.5–8.5 (mildly alkaline)
Red-brown	pH 8.5+ (strongly alkaline)

Turmeric paper: Soak strips of absorbent paper in turmeric solution, allow to dry, and store in a dark container. These strips test lye strength quickly — a strong red color confirms adequate alkalinity for soapmaking.

Blackberries and Blueberries

Anthocyanin pigments in dark berries behave similarly to red cabbage. The fresh juice or a water extract works as an indicator.

Preparation: Crush fresh or frozen berries through a cloth. The dark juice is ready to use directly. For a more concentrated indicator, simmer the juice gently to reduce volume by half.

Color behavior:

Color	Condition
Red-pink	Strongly acidic (pH 1–4)
Purple	Mildly acidic to neutral (pH 4–7)
Blue-green	Mildly alkaline (pH 7–9)
Yellow-green	Strongly alkaline (pH 9+)

Elderberries, mulberries, and dark grapes behave similarly. The more intensely pigmented the raw berry, the better it works as an indicator.

Beets (Beta vulgaris)

Beet juice contains betacyanin, a red pigment that behaves somewhat differently from anthocyanins. It is red in acidic and neutral conditions, turning yellow-brown only in strongly alkaline conditions (pH above 11). Beet juice is less useful for detecting mild alkalis but reliable for flagging dangerous concentrations of lye.

Preparation: Grate raw beet, squeeze juice through cloth. Use directly or dilute 1:1 with water.

Best use: Testing very strong lye solutions. If beet juice turns yellow-brown, the solution is dangerously alkaline. If it stays red, the solution is below pH 11.

Grape Juice and Red Wine

The anthocyanins in red grape juice or young red wine shift from red in acidic conditions through purple at neutral to blue-green in alkaline conditions. The color changes are subtle but reliable. Red wine that has soured to vinegar (now acidic) will stay noticeably redder than the same wine treated with wood ash lye (now alkaline).

Hibiscus Flowers

Dried hibiscus petals (Hibiscus sabdariffa, used in herbal teas) steeped in hot water produce a deep red liquid that turns blue-green in alkaline conditions. The color shift is vivid and easy to read.

Preparation: Steep 10 grams of dried petals in 200 mL of boiling water for 10 minutes. Filter and cool before use. Store in a sealed container — the pigment oxidizes over time.

Making and Storing Indicator Papers

Indicator papers are more practical than liquid extracts for field use. They last weeks to months if stored correctly.

Steps:

1. Prepare a concentrated indicator extract (any of the above methods).
2. Cut coffee filter paper, blotting paper, or any absorbent paper into strips approximately 1 cm wide and 10 cm long.
3. Soak strips fully in the indicator solution for 2 minutes.
4. Hang or lay flat to air dry completely — do not heat, as this can alter the pigment.
5. Store in a sealed glass jar or wrapped in wax paper, away from light and moisture.

Testing: Touch the dry strip to the liquid being tested, or add one drop to the strip. Read the color within 30 seconds. Rinse the strip with clean water to see if color reversal occurs (genuine pH shift, not contamination).

Limitations

Natural indicators are qualitative, not quantitative. They tell you roughly where on the pH scale a substance falls, but not the exact value. For precision work, use multiple indicator types and compare results.

Cross-Checking with Multiple Indicators

Using two or three indicators on the same unknown solution narrows the range considerably.

Example: Testing a lye solution

Indicator	Result	Interpretation
Red cabbage	Yellow-green	pH 10+
Turmeric paper	Red-brown	pH 8.5+
Beet juice	Still red	pH below 11

Conclusion: pH is approximately 9–10. Lye is alkaline but not yet at soapmaking strength (which typically needs pH 12+).

Preserving Indicators Over Time

Fresh juice extracts deteriorate within days at room temperature. Extend shelf life with these methods:

• Alcohol preservation: Add 20% grain alcohol to the extract. This prevents mold and bacterial growth, extending shelf life to several weeks.
• Drying: Paper strips last longest — properly dried strips can remain usable for 3–6 months.
• Freezing: If ice is available, freeze small amounts of concentrated extract in stoppered containers.
• Dark storage: Light degrades anthocyanins rapidly. Always store in opaque or dark-glass containers.

Seasonal Harvesting Strategy

Plan collection to span the full year:

Season	Best sources
Spring	Young red cabbage leaves, rhubarb juice
Summer	Fresh blackberries, elderberries, hibiscus flowers
Autumn	Blueberries, dark grapes, beet harvest
Winter	Dried turmeric, stored dried hibiscus, fermented berry extracts

Dry and preserve summer and autumn harvests specifically for winter and spring use. A community with a well-stocked indicator supply can conduct basic chemistry year-round.