This is getting there.
Now, what you need is a way to quantify the degree of reduction in a stain - this can be an objective chemical test or even a subjective numerical score by unbiased "judges", but if the latter you need to define ahead of time the criteria for making the score and, ideally, some kind of objective metric or metrics against which the score could be determined. For example, stains are primarily visible in nature. Is there any experiment you can think of to gauge the visible impact of a stain?
You also should identify a hypothesis, specify test materials you will use, determine any important aspects of the experiment method - including the number of samples/replicates you intend to measure as well as any important controls, and decide how data will be analyzed (including any statistical methods). It is always a good idea to also think about what the limitations of your approach are before you actually do any work, as this will help you determine whether your method is adequate to test your hypothesis.