Turmeric Paper

Quick Answer: Turmeric Paper is filter paper dyed with turmeric, whose yellow pigment curcumin turns red-brown in alkaline conditions and also reacts with boric acid; it is used as a simple indicator paper for bases and as the classic test paper for borates.

How Turmeric Paper Works

Curcumin, the colouring matter of the turmeric root, is yellow in acidic and neutral solutions and turns red-brown as the pH rises into the alkaline region, with the change becoming clear at roughly pH 8 and above. A strip dipped into limewater, soap solution or dilute sodium hydroxide therefore reddens, while vinegar or lemon juice leaves it yellow. The same change can be seen at home when a curry stain turns red after contact with soap.

Its second, more specialised use is the borate test. When the paper is moistened with a sample containing boric acid or a borate that has been acidified with dilute hydrochloric acid, and then dried gently, it develops a rose-red to red-brown colour as curcumin combines with boric acid. A drop of dilute alkali on that area turns it greenish-black to blue-black, which helps separate the borate result from the ordinary alkali response.

As a general acid-base indicator, curcumin gives a less sharp change than litmus or phenolphthalein, but turmeric paper is inexpensive, safe to handle and links chemistry lessons to a familiar kitchen spice, which is why it features in many school practical courses.

Classroom and Lab Uses

• Introducing natural indicators alongside red cabbage extract and litmus in middle-school science.
• Testing household substances such as soap, baking soda solution and vinegar.
• The qualitative test for borate or boric acid in inorganic salt analysis.
• Checking surfaces or rinse water for residual alkali.

Specifications

Care & Handling

• Store the strips in a closed container away from light, which fades curcumin.
• Keep them away from ammonia and other alkaline fumes in the prep room.
• Handle strips with dry fingers or forceps, and apply test liquids with a glass rod.

Why Choose LabEquip

Schools running natural-indicator practicals and colleges teaching salt analysis are the main buyers of this paper. LabEquip lists it with the other test papers in its General Lab Products section, including Phenolphthalein Paper for a sharper alkali test, and class supplies can be arranged through the contact page.

Frequently Asked Questions

What colour does turmeric paper turn in a base?

It changes from yellow to red-brown in alkaline solutions such as soap solution, limewater or dilute sodium hydroxide. In acids and neutral water it stays yellow.

Can turmeric paper detect acids?

Not directly, because it stays yellow in both acidic and neutral solutions. To tell an acid from a neutral solution, use blue litmus or a pH indicator paper instead.

How is it used to test for borates?

The sample is acidified with dilute hydrochloric acid, the paper is moistened with it and dried gently. A red-brown colour indicates boric acid or borate, and a drop of alkali then turns that colour greenish-black.

Why do schools use it when litmus is available?

It shows that indicators occur in nature, links to a familiar spice and is safe to handle. Teachers often set it beside litmus and red cabbage extract so students can compare indicators.

Does the paper lose its colour over time?

Curcumin slowly fades in light and air, so old paper gives weaker colours. Store it closed and in the dark, and try a strip in a known alkali if the yellow looks pale.

Can the alkali colour change be reversed?

Yes, the red-brown alkali colour returns towards yellow if the strip is then dipped in acid, because that change depends only on pH. The borate colour behaves differently, which is why the alkali step is used to confirm it.

Last Updated: September 2026