Phenolphthalein is the most commonly quoted pH indicator for doing oil titrations, but it is expensive and can be hard to find.
Can we use anything else?
Yes! Turmeric makes a cheap and effective alternative to phenolphthalein. Turmeric is a bright yellow spice with subtle flavour, used widely in Asian cooking. You should be able to find it on the spice shelves of most food stores who stock Indian spices.
Word of warning - Turmeric will stain any surface you spill it on.
Preparation - a pinch of turmeric in 100ml of isopropyl alcohol is plenty. Here's a short video to show you the colour changes for alkali and acid conditions, with phenolphthalein and turmeric side by side.
You can also demonstrate simple photography with turmeric - this makes an ideal childrens' lesson in photo-sensitivity.
Dissolve a spoonfull of turmeric powder in 100ml of isopropyl alcohol (isopropanol). Not all the turmeric will dissolve, don't worry about that.
In a well shaded area, paint a sheet of white paper with the yellow turmeric solution, and allow it to fully dry in the dark.
When dry, arrange some common household articles, with clear sihouettes, over the surface of the paper.
Now place the paper outside in direct sunlight for 15 minuites - don't move the articles you placed on the paper during that period.
Bring the paper indoors after 15 minutes, remove the articles from the paper and you should have a clear 'contact-print' to demonstrate simple photography.
The ultraviolet light in the sunshine affects the yellow pigment in turmeric, breaking the molecule to form a non-coloured variant. Anywhere the sun was allowed to shine now looks white or very pale yellow. Any area left in the shade remains dark yellow.
The photograph will fade quite quickly over the next day or 2, so is not a permanent photograph.