Expert: George Maxwell - 10/5/2007

Question
I'm doing science fair and i need to know how to record a percent of stain removed after wash. Please Reply thanks. =]
-The Bowlmer-nator

Answer
Hi, and thanks for the question.

Right off, it's goinig to be difficult to calculate an actual percentage number: stains are caused by very small amounts of a substance, and often a stain involves a chemical change in the material that's stained.

It'd be very difficult to measure the weight or volume of the stain, whhich would be an important part of percetage calcultions. Othere methods (usinng colourimetry or absorbance spectroscopy) are too expensive and complex.

To mesure the effectivenes of different washing powders, you could try making small strips of a test material (e.g. 1" by 1" squares of cotton material from a whit t-shirt).

Then, soak them each in the same staining material and leave them to dry. You now have a selection of identically stained materials. Put them each in a wash with a different washing powder. When they've all been washed, laay them ot sde by side, along with a sample of unstained cotton, and you can compare the effectivenes of the powders by how clean the samples look. You could then repeat the experiment with other materials.

It's important that your report /exhibit explains the reason you choose a particular method. You may also want to point out that the customer buying washing powder / a washing machine won't be impressed because it "removes 56% of a stain", they'll go by what the garment looks like when it's been washed.

Hope this helps.