Method of measuring harshness of a surfactant

A method of measuring harshness of a surfactant, comprising the steps of:

• i) preparing a solid protein-dye complex comprising:
• a) a protein, which is a non-denatured corn protein and which is soluble in aqueous alcohol;
• and
• b) a protein binding dye, which binds specifically to the protein (a);
• by dissolving a) and b) in aqueous alcohol to form a solution of protein-dye complex;
• and
• removing the aqueous alcohol to form a solid protein-dye complex;
• ii) providing an aqueous solution of a surfactant and taking a first colour measurement of the aqueous solution;
• iii) adding the solid protein-dye complex to the aqueous solution of the surfactant, taking a second colour measurement of the aqueous solution and measuring a change in intensity of the colour between the first colour measurement and the second colour measurement;
• and
• iv) matching the change in intensity of the colour with a reference scale to determine the harshness of the surfactant.