Mix the citric acid and the bicarbonate and add a few drops of food colouring if desired and a few drops of essential oil to make it smell nice.
Add, drop by drop, sunflower oil while mixing. Keep mixing until the mixture starts to stick to the sides of the bowl.
Tip the mixture into cling film and using the cling film as a barrier, so not to touch the mixture, shape the mixture into a ball. Leave to dry over night. If you've added too much oil it may be a bit sticky in the morning, but it works just as good. Store in a dry place.