There is a paper where the authors use ketchup for polishing high precision lenses. The especially want to have the property of the shear-thinning for best results: https://www.spiedigitallibrary.org/conference-proceedings-of...

To be clear, there are better polishing agents in the scenarion than ketchup. On of the authors mentions that they wanted to do some research that could get them the IG Nobelprice.