This science experiment goes well with grade 7 pure substances and mixtures unit. Students have been requested by Genghis Khan to test samples of ink to see which is pure and which is a mixture of pigments. The premise of the setup is that Genghis Khan is looking to import ink for his scribes that is of high quality to document his great accomplishments. Students will use chromatography to check the different inks then write a report back to Khan. The letter hook, success criteria, teacher guide and student worksheet are included in the file. An audio recording of the letter that I made is also available if interested by emailing me (no charge).