Blood stain or red ink

I scratched my itchy back while I was reading a book with my daughter last night. This act tore off a clot of an age-old wound on my back and immediately blood was seeping out. I soaked the blood with a tissue paper and my daughter kept on asking what the 'red stuff' was. I told her that it was blood that stained the paper red. She then sketched a red line on the paper with a colour pen and asked me how to distanguish red ink from blood stains.

Her question reminded me of a book named 'Crime scene investigation for grade 6-12'. I learnt from this book a simple way of telling the difference between blood stains and red ink. The chemical reagent needed for the test is commonly available in all first aid box- it is hydrogen peroxide. I added a few drops of hydrogen peroxide to the blood stains and gas bubbles emerged right away. I did the same thing on red ink and nothing visible occurred.

The scientific principle behind is comprehensible to all senior form science students. As blood cells contain an enzyme known as catalase, hydrogen peroxide acts as the substrate for the catase to carry out catabolic reaction that produces oxygen and water. The bubbles evolved are oxygen gas. This explains why blood stains and red ink behave differently when reacting with hydrogen peroxide.

Apart from using hydrogen peroxide as a test reagent, can you think of other ways of distinguishing blood stains from red ink?